Neural Development Notes PDF

Summary

These notes cover neural development, focusing on topics including neural induction, body pattern formation, neurogenesis, and cell migration. The document is for the academic year 2024-2025, providing insights into different developmental stages and underlying mechanisms.

Full Transcript

‭NEURAL DEVELOPMENT – Prof.sse S. Bovetti – A.A 2024-2025 – anno1 semestre1 – Margherita Bosso‬ ‭Serena Bovetti‬ ‭AA 2024 2025‬ ‭ANNO 1 - SEMESTRE...

‭NEURAL DEVELOPMENT – Prof.sse S. Bovetti – A.A 2024-2025 – anno1 semestre1 – Margherita Bosso‬ ‭Serena Bovetti‬ ‭AA 2024 2025‬ ‭ANNO 1 - SEMESTRE 1‬ ‭1‬ ‭NEURAL DEVELOPMENT – Prof.sse S. Bovetti – A.A 2024-2025 – anno1 semestre1 – Margherita Bosso‬ ‭Sommario‬ ‭Lesson1‬‭-‬‭07.11‬‭(Prof.ssa‬‭Bovetti)‬‭.....................................................................................................................................................‬‭5‬ ‭PROGRAM:‬‭.......................................................................................................................................................................‬‭5‬ ‭NEURAL‬‭INDUCTION‬‭...............................................................................................................................................................................................‬‭5‬ ‭Evolutionary‬‭origins‬‭of‬‭metazoans‬‭.....................................................................................................................................................................‬‭5‬ ‭An‬‭historical‬‭point‬‭of‬‭view‬‭..........................................................................................................................................................................‬‭5‬ ‭C.‬‭Elegans‬‭development‬‭............................................................................................................................................................................‬‭6‬ ‭Experiment‬‭on‬‭C.elegans‬‭cell‬‭division:‬‭......................................................................................................................................‬‭7‬ ‭Amphibian‬‭embryonic‬‭development‬‭...........................................................................................................................................................‬‭8‬ ‭Mammalian‬‭embryonic‬‭development‬‭.........................................................................................................................................................‬‭8‬ ‭Neural‬‭tube‬‭defects‬‭..................................................................................................................................................................‬‭10‬ ‭Demonstrating‬‭self-regulation‬‭in‬‭embryos‬‭...............................................................................................................................................‬‭10‬ ‭1891‬‭-‬‭Driesch‬‭..........................................................................................................................................................................‬‭11‬ ‭1903‬‭-‬‭Spemann‬‭......................................................................................................................................................................‬‭11‬ ‭1903‬‭-‬‭Weismann‬‭.....................................................................................................................................................................‬‭11‬ ‭Spemann‬‭(optic‬‭cup)‬‭................................................................................................................................................................‬‭11‬ ‭Anchor‬‭point‬‭(Spemann‬‭and‬‭Mangold)‬‭....................................................................................................................................‬‭11‬ ‭Identifying‬‭molecules‬‭that‬‭mediate‬‭neural‬‭induction‬‭................................................................................................................................‬‭12‬ ‭Signals‬‭from‬‭the‬‭organizer‬‭.......................................................................................................................................................‬‭12‬ ‭What‬‭organizes‬‭the‬‭organizer?‬‭................................................................................................................................................‬‭13‬ ‭Mechanisms‬‭on‬‭BMP‬‭working‬‭.................................................................................................................................................‬‭13‬ ‭Summary‬‭-‬‭lesson1‬‭..................................................................................................................................................................................‬‭14‬ ‭Lesson2‬‭-‬‭14.11‬‭(Prof.ssa‬‭Bovetti)‬‭...................................................................................................................................................‬‭14‬ ‭DEVELOPMENT‬‭OF‬‭A‬‭BODY‬‭PATTERN‬‭...............................................................................................................................................................‬‭14‬ ‭PATTERNING‬‭OF‬‭THE‬‭NEUROECTODERM‬‭..................................................................................................................................................‬‭14‬ ‭Development‬‭in‬‭Drosophila‬‭......................................................................................................................................................‬‭14‬ ‭Patterns‬‭of‬‭gene‬‭expression‬‭are‬‭set-up‬‭by‬‭morphogens‬‭.........................................................................................................................‬‭15‬ ‭Establishing‬‭polarity‬‭in‬‭the‬‭egg‬‭................................................................................................................................................................‬‭16‬ ‭Patterning‬‭in‬‭the‬‭AP‬‭axis‬‭of‬‭the‬‭vertebrate‬‭CNS‬‭..............................................................................................................................................‬‭17‬ ‭Bicoid‬‭.......................................................................................................................................................................................‬‭17‬ ‭The‬‭cascade‬‭of‬‭gene‬‭regulation‬‭in‬‭fruit‬‭flies‬‭............................................................................................................................................‬‭18‬ ‭Hox‬‭genes‬‭................................................................................................................................................................................................‬‭19‬ ‭Evolutionary‬‭tree‬‭of‬‭vertebrates‬‭...............................................................................................................................................‬‭20‬ ‭Development‬‭of‬‭vertebrate‬‭nervous‬‭system‬‭............................................................................................................................................‬‭21‬ ‭Patterning‬‭in‬‭the‬‭DV‬‭axis‬‭of‬‭the‬‭vertebrate‬‭CNS‬‭..............................................................................................................................................‬‭22‬ ‭Signals‬‭gradients‬‭that‬‭drive‬‭DV‬‭patterning‬‭in‬‭vertebrates‬‭........................................................................................................‬‭22‬ ‭Summary‬‭-‬‭lesson2‬‭..................................................................................................................................................................................‬‭23‬ ‭Lesson3‬‭-‬‭21.11‬‭(Prof.ssa‬‭Bovetti)‬‭...................................................................................................................................................‬‭24‬ ‭NEUROGENESIS‬‭AND‬‭CELL‬‭MIGRATION‬‭............................................................................................................................................................‬‭24‬ ‭Neurogenesis‬‭...................................................................................................................................................................................................‬‭24‬ ‭Symmetrical‬‭and‬‭asymmetrical‬‭neural‬‭divisions‬‭......................................................................................................................‬‭24‬ ‭The‬‭developing‬‭cerebral‬‭cortex‬‭................................................................................................................................................................‬‭25‬ ‭Symmetric‬‭and‬‭Asymmetric‬‭cell‬‭divisions‬‭................................................................................................................................................‬‭26‬ ‭Asymmetric‬‭cell‬‭division‬‭in‬‭Drosophila‬‭.....................................................................................................................................‬‭26‬ ‭Asymmetric‬‭cell‬‭division‬‭in‬‭vertebrates‬‭....................................................................................................................................‬‭27‬ ‭Postmitotic‬‭neuronal‬‭differentiation‬‭..........................................................................................................................................................‬‭27‬ ‭Proneural‬‭genes‬‭in‬‭Drosophila‬‭-‬‭Mutual‬‭lateral‬‭inhibition‬‭........................................................................................................‬‭27‬ ‭Proneural‬‭genes‬‭in‬‭vertebrates‬‭-‬‭Mutual‬‭lateral‬‭inhibition‬‭........................................................................................................‬‭28‬ ‭Neurogenesis‬‭in‬‭adult‬‭brain‬‭.............................................................................................................................................................................‬‭28‬ ‭Adult‬‭neurogenesis:‬‭the‬‭olfactory‬‭epithelium‬‭...........................................................................................................................................‬‭28‬ ‭Adult‬‭neurogenesis:‬‭The‬‭SVZ‬‭and‬‭Olfactory‬‭Bulb‬‭(OB)‬‭neurogenesis‬‭....................................................................................................‬‭29‬ ‭Neuronal‬‭migration‬‭...........................................................................................................................................................................................‬‭29‬ ‭Direct‬‭visualization‬‭...................................................................................................................................................................‬‭29‬ ‭Indirect‬‭visualization‬‭................................................................................................................................................................‬‭30‬ ‭Major‬‭modes‬‭of‬‭migration‬‭........................................................................................................................................................................‬‭31‬ ‭1-‬‭Individual‬‭migration‬‭:‭.‬...........................................................................................................................................................‬‭31‬ ‭2-‬‭Chain‬‭migration:‬‭..................................................................................................................................................................‬‭32‬ ‭3-‬‭Scaffold‬‭migration:‬‭...............................................................................................................................................................‬‭32‬ ‭Defect‬‭in‬‭neuronal‬‭migration:‬‭GnRH‬‭neurons‬‭-‬‭GnRH‬‭cells‬‭migration‬‭and‬‭Kallmann‬‭Syndrome‬‭............................................‬‭33‬ ‭Summary‬‭-‬‭lesson3‬‭..................................................................................................................................................................................‬‭34‬ ‭Lesson4‬‭-‬‭28.11‬‭(Prof.ssa‬‭Bovetti)‬‭...................................................................................................................................................‬‭34‬ ‭MATURATION‬‭OF‬‭FUNCTIONAL‬‭PROPERTIES‬‭...................................................................................................................................................‬‭34‬ ‭2‬ ‭NEURAL DEVELOPMENT – Prof.sse S. Bovetti – A.A 2024-2025 – anno1 semestre1 – Margherita Bosso‬ ‭How‬‭neurons‬‭develop‬‭their‬‭shapes‬‭.................................................................................................................................................‬‭34‬ ‭The‬‭cytoskeleton‬‭in‬‭mature‬‭axons‬‭and‬‭dendrites‬‭....................................................................................................................................‬‭35‬ ‭The‬‭growing‬‭neurite‬‭.................................................................................................................................................................................‬‭35‬ ‭Stages‬‭of‬‭neurite‬‭outgrowth‬‭.....................................................................................................................................................................‬‭36‬ ‭Regulation‬‭of‬‭dendrite‬‭morphology‬‭..........................................................................................................................................................‬‭37‬ ‭1.‬‭Interaction‬‭between‬‭SISTER‬‭DENDRITES‬‭of‬‭the‬‭same‬‭neuron‬‭..................................................................................................‬‭38‬ ‭2.‬‭Between‬‭dendrites‬‭of‬‭NEIGHBORING‬‭NEURONS‬‭OF‬‭DIFFERENT‬‭TYPE‬‭................................................................................‬‭39‬ ‭3.‬‭Between‬‭dendrites‬‭of‬‭NEIGHBORING‬‭NEURONS‬‭OF‬‭THE‬‭SAME‬‭TYPE‬‭..................................................................................‬‭40‬ ‭SYNAPTOGENESIS‬‭AND‬‭SPINOGENESIS‬‭...........................................................................................................................................................‬‭40‬ ‭Precursors‬‭to‬‭synapses‬‭...........................................................................................................................................................‬‭40‬ ‭Evolution‬‭of‬‭synapses‬‭..............................................................................................................................................................................‬‭41‬ ‭The‬‭structure‬‭of‬‭a‬‭(excitatory)‬‭synapse‬‭....................................................................................................................................................‬‭42‬ ‭Stages‬‭of‬‭synaptogenesis‬‭........................................................................................................................................................................‬‭42‬ ‭1.‬‭Synaptic‬‭specification‬‭and‬‭induction‬‭....................................................................................................................................‬‭43‬ ‭2.‬‭Synapse‬‭formation‬‭...............................................................................................................................................................‬‭44‬ ‭3.‬‭Synapse‬‭selection‬‭and‬‭stabilization‬‭.....................................................................................................................................‬‭44‬ ‭The‬‭neuromuscular‬‭junctions‬‭...................................................................................................................................................................‬‭45‬ ‭Spinogenesis‬‭...........................................................................................................................................................................................‬‭46‬ ‭Molecular‬‭regulators‬‭of‬‭spine‬‭development‬‭.............................................................................................................................................‬‭47‬ ‭Dendritic‬‭spines‬‭compete‬‭for‬‭survival‬‭......................................................................................................................................‬‭47‬ ‭Fragile‬‭X‬‭syndrome‬‭suggests‬‭there‬‭can‬‭be‬‭too‬‭much‬‭of‬‭a‬‭good‬‭thing‬‭.....................................................................................................‬‭48‬ ‭In‬‭Vivo‬‭Optical‬‭Imaging‬‭of‬‭FXS‬‭Model‬‭Mice‬‭.....................................................................................................................................‬‭48‬ ‭Altered‬‭Structural‬‭and‬‭Functional‬‭Synaptic‬‭Plasticity‬‭with‬‭Motor‬‭Skill‬‭Learning‬‭in‬‭a‬‭Mouse‬‭Model‬‭of‬‭Fragile‬‭X‬‭Syndrome‬‭............‬‭49‬ ‭Dendritic‬‭Spines‬‭in‬‭Early‬‭Postnatal‬‭Fragile‬‭X‬‭Mice‬‭Are‬‭Insensitive‬‭to‬‭Novel‬‭Sensory‬‭Experience‬‭..................................................‬‭49‬ ‭Hypersensitivity‬‭in‬‭response‬‭to‬‭sensory‬‭stimuli‬‭and‬‭neocortical‬‭hyperexcitability‬‭are‬‭prominent‬‭features‬‭of‬‭Fragile‬‭X‬‭Syndrome‬‭.‬‭50‬ ‭Lesson‬‭5‬‭-‬‭2.12‬‭(Prof.ssa‬‭Bovetti)‬‭...................................................................................................................................................‬‭51‬ ‭ADVANCED‬‭OPTICAL‬‭IMAGING‬‭TECHNIQUES‬‭FOR‬‭NEURAL‬‭DEVELOPMENT‬‭..............................................................................................‬‭51‬ ‭Analyzing‬‭structure‬‭and‬‭function‬‭..............................................................................................................................................................‬‭51‬ ‭Light‬‭scattering‬‭in‬‭biological‬‭tissue‬‭..........................................................................................................................................................‬‭52‬ ‭Properties‬‭of‬‭light‬‭.............................................................................................................................................................................‬‭52‬ ‭Principles‬‭of‬‭fluorescence‬‭................................................................................................................................................................‬‭52‬ ‭Wide‬‭field‬‭illumination‬‭......................................................................................................................................................................‬‭53‬ ‭Confocal‬‭illumination‬‭........................................................................................................................................................................‬‭53‬ ‭Principles‬‭of‬‭two-photon‬‭excitation‬‭..........................................................................................................................................................‬‭54‬ ‭Why‬‭non-linear‬‭is‬‭more‬‭than‬‭linear?‬‭................................................................................................................................................‬‭55‬ ‭Multiphoton‬‭system‬‭..................................................................................................................................................................................‬‭55‬ ‭Nikon‬‭A1‬‭two-photon‬‭microscope‬‭@‬‭NICO‬‭.....................................................................................................................................‬‭56‬ ‭Fluorescent‬‭tools‬‭for‬‭2P‬‭imaging‬‭.............................................................................................................................................................‬‭56‬ ‭Fluorescent‬‭reporters‬‭of‬‭cell‬‭activity‬‭........................................................................................................................................................‬‭57‬ ‭The‬‭Calcium‬‭Ion‬‭as‬‭an‬‭Indirect‬‭Reporter‬‭of‬‭Neuronal‬‭Activity‬‭.................................................................................................‬‭57‬ ‭In‬‭vivo‬‭two‬‭photon‬‭calcium‬‭imaging‬‭.........................................................................................................................................................‬‭58‬ ‭Light‬‭scattering‬‭in‬‭biological‬‭tissue‬‭..........................................................................................................................................................‬‭58‬ ‭Image‬‭the‬‭whole‬‭mouse‬‭brain:‬‭the‬‭problem‬‭of‬‭tissue‬‭scattering‬‭......................................................................................................‬‭59‬ ‭Light-sheet‬‭fluorescence‬‭microscopy‬‭..............................................................................................................................................‬‭59‬ ‭Confocal‬‭imaging‬‭.....................................................................................................................................................................‬‭60‬ ‭Summary‬‭-‬‭lesson‬‭5‭.‬................................................................................................................................................................................‬‭60‬ ‭Lesson‬‭6‬‭-‬‭05.12‬‭(Stefano‬‭Zucca‬‭-‬‭seminar)‬‭............................................................................................................................................‬‭60‬ ‭Basic‬‭concepts‬‭in‬‭biophysics‬‭...........................................................................................................................................................................‬‭61‬ ‭Neurons‬‭...................................................................................................................................................................................................‬‭61‬ ‭Cell‬‭potential‬‭............................................................................................................................................................................................‬‭61‬ ‭Ions’‬‭flow‬‭across‬‭the‬‭membrane‬‭..............................................................................................................................................‬‭61‬ ‭How‬‭is‬‭ion‬‭flow‬‭regulated?‬‭.......................................................................................................................................................‬‭61‬ ‭Ion‬‭channels‬‭............................................................................................................................................................................‬‭62‬ ‭Ions’‬‭permeability‬‭.....................................................................................................................................................................‬‭62‬ ‭Recording‬‭neuronal‬‭electrical‬‭properties‬‭.........................................................................................................................................................‬‭63‬ ‭Patch‬‭clamp‬‭.............................................................................................................................................................................................‬‭63‬ ‭Scheme‬‭Patch-Clamp‬‭Recordings‬‭...........................................................................................................................................‬‭63‬ ‭Patch-‬‭Clamp:‬‭Voltage-Clamp‬‭vs‬‭Current-Clamp‬‭....................................................................................................................‬‭64‬ ‭Intrinsic‬‭neuronal‬‭properties‬‭.............................................................................................................................................................................‬‭65‬ ‭Biophysics‬‭of‬‭the‬‭Action‬‭Potential‬‭............................................................................................................................................................‬‭66‬ ‭Developmental‬‭changes‬‭of‬‭Action‬‭Potential‬‭properties‬‭...........................................................................................................‬‭67‬ ‭Role‬‭of‬‭Ca++‬‭............................................................................................................................................................................‬‭67‬ ‭Neuronal‬‭chemical‬‭communication‬‭during‬‭development‬‭.................................................................................................................................‬‭68‬ ‭3‬ ‭NEURAL DEVELOPMENT – Prof.sse S. Bovetti – A.A 2024-2025 – anno1 semestre1 – Margherita Bosso‬ ‭GABA‬‭receptors‬‭.......................................................................................................................................................................‬‭68‬ ‭Summary‬‭-‬‭Intrinsic‬‭neuronal‬‭properties‬‭..................................................................................................................................................‬‭69‬ ‭Microbial‬‭opsins‬‭.......................................................................................................................................................................................‬‭69‬ ‭Light‬‭Control‬‭of‬‭Protein‬‭Activity‬‭................................................................................................................................................................‬‭72‬ ‭Summary‬‭-‬‭Optogenetics‬‭.........................................................................................................................................................................‬‭72‬ ‭Application‬‭of‬‭2P‬‭in‬‭vivo‬‭imaging‬‭-‬‭SEE‬‭LESSON‬‭8‭.‬...............................................................................................................................‬‭72‬ ‭Lesson‬‭7‬‭-‬‭12.12‬‭(Prof.‬‭Bovetti)‬‭.......................................................................................................................................................‬‭74‬ ‭ACTIVITY-GUIDED‬‭NEURAL‬‭DEVELOPMENT‬‭-‬‭MAP‬‭FORMATION‬‭....................................................................................................................‬‭74‬ ‭Coarse‬‭maps‬‭....................................................................................................................................................................................................‬‭75‬ ‭Fine‬‭maps:‬‭topographic‬‭maps‬‭..........................................................................................................................................................................‬‭75‬ ‭Fine‬‭maps:‬‭feature‬‭maps‬‭.................................................................................................................................................................................‬‭76‬ ‭Principles‬‭of‬‭map‬‭formation‬‭.............................................................................................................................................................................‬‭76‬ ‭Development‬‭of‬‭topographic‬‭maps‬‭..................................................................................................................................................................‬‭76‬ ‭Development‬‭of‬‭topographic‬‭maps:‬‭the‬‭chemoaffinity‬‭hypothesis‬‭...........................................................................................‬‭78‬ ‭Neuronal‬‭activity:‬‭tectal‬‭expansion‬‭or‬‭compression‬‭rearrangements‬‭......................................................................................‬‭79‬ ‭Map-formation:‬‭the‬‭role‬‭of‬‭neuronal‬‭activity‬‭.....................................................................................................................................................‬‭79‬ ‭Map-formation:‬‭the‬‭role‬‭of‬‭neuronal‬‭activity‬‭(segregation‬‭in‬‭humans)‬‭.....................................................................................‬‭79‬ ‭EXPERIMENT1‬‭-‬‭discovery‬‭of‬‭segregation‬‭.............................................................................................................................‬‭80‬ ‭EXPERIMENT2‬‭-‬‭induction‬‭of‬‭segregation,‬‭The‬‭Three-Eyed‬‭Frogs‬‭experiment‬‭.....................................................................‬‭80‬ ‭Spontaneous‬‭activity‬‭role‬‭.........................................................................................................................................................................‬‭82‬ ‭Spontaneous‬‭activity‬‭and‬‭formation‬‭of‬‭segregation‬‭.................................................................................................................‬‭82‬ ‭Paper‬‭.......................................................................................................................................................................................................‬‭82‬ ‭Spontaneous‬‭Waves‬‭of‬‭Retinal‬‭Activity‬‭Form‬‭Ocular‬‭Dominance‬‭Bands‬‭in‬‭the‬‭LG‬‭................................................................‬‭83‬ ‭Hebbian‬‭synapse‬‭-‬‭Hebbian‬‭process‬‭.......................................................................................................................................................‬‭83‬ ‭Long-term‬‭potentiation‬‭(LTP)‬‭confirms‬‭the‬‭existence‬‭of‬‭Hebbian‬‭synapses‬‭............................................................................‬‭83‬ ‭Paper‬‭-‬‭LTP‬‭..............................................................................................................................................................................................‬‭84‬ ‭Summary‬‭-‬‭lesson‬‭“MAP‬‭FORMATION”‬‭..................................................................................................................................................‬‭84‬ ‭DEVELOPMENT‬‭OF‬‭FEATURE‬‭MAPS‬‭...................................................................................................................................................................‬‭85‬ ‭EXPERIMENT:‬‭David‬‭Hubel,‬‭Torsten‬‭Wiesel‬‭-‬‭fine‬‭maps‬‭........................................................................................................‬‭85‬ ‭Development‬‭of‬‭orientation‬‭and‬‭direction‬‭maps‬‭in‬‭the‬‭ferret‬‭visual‬‭cortex‬‭..............................................................................................‬‭85‬ ‭Visual‬‭cortex‬‭of‬‭ferret‬‭grown‬‭up‬‭in‬‭dark‬‭environment‬‭..............................................................................................................‬‭86‬ ‭Lesson‬‭8‬‭-‬‭19.12‬‭(Prof.ssa‬‭Bovetti)‬‭.................................................................................................................................................‬‭86‬ ‭EXPERIENCE-DEPENDENT‬‭NEURAL‬‭DEVELOPMENT‬‭......................................................................................................................................‬‭86‬ ‭Effect‬‭of‬‭experience‬‭on‬‭visual‬‭system‬‭development‬‭........................................................................................................................................‬‭87‬ ‭Experiment:‬‭Effect‬‭of‬‭experience‬‭on‬‭visual‬‭system‬‭development‬‭............................................................................................................‬‭87‬ ‭(David‬‭Hubel‬‭and‬‭Torsten‬‭Wiesel)‬‭...........................................................................................................................................‬‭87‬ ‭Effects‬‭of‬‭strabismus‬‭on‬‭physiological‬‭responses‬‭of‬‭neurons‬‭in‬‭the‬‭visual‬‭cortex‬‭...........................................................................‬‭88‬ ‭Physiological‬‭changes‬‭in‬‭ocular‬‭dominance‬‭prior‬‭to‬‭anatomical‬‭changes‬‭.......................................................................................‬‭89‬ ‭Physiological‬‭changes‬‭in‬‭ocular‬‭dominance‬‭prior‬‭to‬‭anatomical‬‭changes‬‭...............................................................................................‬‭90‬ ‭Mammals‬‭require‬‭visual‬‭experience‬‭during‬‭a‬‭sensitive‬‭period‬‭to‬‭develop‬‭functional‬‭vision‬‭............................................................................‬‭90‬ ‭CRITICAL‬‭PERIODS‬‭(CP)‬‭...............................................................................................................................................................................‬‭91‬ ‭Inhibitory‬‭circuits‬‭of‬‭GABA‬‭signalling‬‭and‬‭the‬‭sensitive‬‭period‬‭................................................................................................................‬‭92‬ ‭Example‬‭of‬‭multimodal‬‭integration:‬‭..........................................................................................................................................‬‭93‬ ‭SOCIALLY‬‭GUIDED‬‭NEURAL‬‭DEVELOPMENT‬‭....................................................................................................................................................‬‭93‬ ‭PAPER:‬‭Developmental‬‭encoding‬‭of‬‭natural‬‭sounds‬‭in‬‭the‬‭mouse‬‭auditory‬‭cortex‬‭.........................................................................................‬‭93‬ ‭At‬‭which‬‭age‬‭mice‬‭start‬‭to‬‭hear‬‭USVs‬‭and‬‭how‬‭USVs‬‭processing‬‭changes‬‭across‬‭development?‬‭........................................‬‭94‬ ‭In‬‭vivo‬‭2P‬‭functional‬‭imaging‬‭of‬‭sound-evoked‬‭activity‬‭...........................................................................................................‬‭94‬ ‭L2/3‬‭cells‬‭tuned‬‭for‬‭the‬‭same‬‭stimulus‬‭displayed‬‭highly‬‭correlated‬‭spontaneous‬‭activity‬‭.......................................................‬‭96‬ ‭CONCLUSIONS‬‭......................................................................................................................................................................‬‭96‬ ‭How‬‭to‬‭Read‬‭and‬‭Understand‬‭a‬‭Scientific‬‭Paper‬‭................................................................................................................................................‬‭97‬ ‭4‬ ‭NEURAL DEVELOPMENT – Prof.sse S. Bovetti – A.A 2024-2025 – anno1 semestre1 – Margherita Bosso‬ ‭NEURAL DEVELOPMENT‬ ‭ esson1 - 07.11 (Prof.ssa Bovetti)‬ L ‭PROGRAM:‬ ‭‬ ‭Neural induction‬ ‭‬ ‭Development of a body pattern‬ ‭‬ ‭Patterning of the neuroectoderm‬ ‭‬ ‭Neurogenesis and cell migration‬ ‭‬ ‭Maturation of functional properties‬ ‭‬ ‭Synaptogenesis and spinogenesis‬ ‭‬ ‭Activity-guided neural development‬ ‭‬ ‭Experience-dependent neural development‬ ‭‬ ‭Socially guided neural development‬ ‭NEURAL INDUCTION‬ ‭Evolutionary origins of metazoans‬ ‭ t‬ ‭some‬ ‭point‬ ‭natural‬ ‭selection‬ A ‭starts‬ ‭favoring‬ ‭individuals‬ ‭whose‬ ‭cells‬ ‭stayed‬ ‭together‬ ‭to‬ ‭form‬ ‭a‬ ‭multicellular‬ ‭body.‬ ‭In‬ ‭sponges‬ ‭there‬ ‭are‬ ‭specialized‬ ‭cells‬ ‭but‬ ‭no‬ ‭real‬ ‭tissues,‬ ‭no‬ ‭symmetry‬ ‭or‬ ‭regularity in the body shape.‬ ‭600‬ ‭million‬ ‭years‬ ‭ago:‬ ‭first‬ ‭metazoans‬ ‭multicellular‬ ‭animals‬ ‭with‬ ‭a‬ ‭body‬ ‭composed‬ ‭of‬ ‭more‬ ‭than one type of cell like cnidaria.‬ ‭In‬ ‭jellyfish‬ ‭and‬ ‭similar‬ ‭organisms‬ ‭have‬ ‭a‬ ‭basic‬ ‭NS‬ ‭composed‬ ‭by‬ ‭a‬ ‭network‬ ‭of‬ ‭neurons‬ ‭of‬ ‭the‬ ‭same‬ ‭type.‬ ‭Jellyfishes‬ ‭have‬ ‭a‬ ‭digestive‬ ‭system,‬ ‭but‬ ‭not‬ ‭a‬ ‭circulatory‬ ‭system,‬‭so‬‭they’re‬‭able‬‭to‬‭respond‬ ‭to‬‭stimuli‬‭such‬‭as‬‭light,‬‭object‬‭and‬ ‭so‬ ‭they‬ ‭can‬ ‭move‬ ‭in‬ ‭a‬ ‭specific‬ ‭direction:‬ ‭reflexive‬ ‭responses‬ ‭to‬ ‭ ncountering‬ ‭prey‬ ‭or‬ ‭other‬ ‭objects‬ ‭and‬ e ‭specialized‬ ‭sensory‬ ‭cells‬ ‭and‬ ‭connections‬ ‭that‬ ‭coordinate‬ ‭moving‬ ‭toward‬ ‭or‬ ‭away‬ ‭from‬ ‭light,‬ ‭diving‬ ‭in‬ ‭response‬ ‭to‬ ‭rough‬ ‭water,‬ ‭and‬ ‭avoiding‬ ‭rock‬ ‭walls‬ ‭brought‬ ‭to‬ ‭the‬ ‭cellular‬ ‭differentiation‬ ‭and‬ ‭coordination‬ ‭of‬ ‭cell‬ ‭types‬ ‭so‬ ‭we‬ ‭can‬ ‭identify‬ ‭a‬ ‭BODY‬ ‭PLAN‬‭:‬ ‭organization‬ ‭of‬ ‭different‬ ‭cell‬ ‭types‬ ‭to‬ ‭survive‬ ‭and reproduce.‬ ‭The‬ ‭NS‬ ‭is‬ ‭part‬ ‭of‬ ‭the‬ ‭body‬ ‭so‬‭other‬‭parts‬‭of‬ ‭the‬ ‭body‬ ‭are‬ ‭connected‬ ‭with‬ ‭it‬ ‭like‬ ‭heart,‬ ‭eyes,‬ ‭muscles,‬ ‭ecc‬ ‭and‬ ‭the‬ ‭NS‬ ‭is‬ ‭also‬ ‭responsible for coordination of all these parts.‬ ‭An historical point of view‬ ‭‬ A ‭ ristotle‬‭(384–322‬‭bce)‬‭addressed‬‭the‬‭question‬‭of‬‭how‬‭types‬‭of‬‭cells‬‭are‬‭arranged‬‭in‬‭parts‬‭of‬‭the‬‭body‬‭by‬ ‭examining hens’ eggs.‬ ‭○‬ ‭Epigenesis‬‭:‬ ‭the‬ ‭body‬ ‭gradually‬ ‭changes‬ ‭shape,‬ ‭acquiring‬ ‭new‬ ‭structures‬ ‭and‬ ‭growing‬ ‭more‬ ‭complex, with time.‬ ‭5‬ ‭NEURAL DEVELOPMENT – Prof.sse S. Bovetti – A.A 2024-2025 – anno1 semestre1 – Margherita Bosso‬ ‭‬ E ‭ nlightenment‬ ‭(17th‬ ‭and‬ ‭18th‬ ‭centuries):‬ ‭initial‬ ‭use‬ ‭of‬ ‭the‬ ‭microscope‬‭.‬ ‭Robert‬ ‭Hooke‬ ‭called‬‭“‭c‬ ells‬‭”‬‭the‬ ‭different compartments of the cork that he observed with the microscope.‬ ‭‬ ‭Jan‬ ‭Swammerdam‬ ‭(1637–1680)‬ ‭used‬ ‭his‬ ‭microscope‬ ‭to‬ ‭find,‬ ‭tucked‬ ‭inside‬ ‭a‬ ‭caterpillar,‬ ‭the‬ ‭wings‬ ‭and‬ ‭body‬‭of‬‭the‬‭butterfly.‬‭He‬‭concluded‬‭that‬‭the‬‭adult‬‭form‬‭had‬ ‭been tucked inside the juvenile’s body all along.‬ ‭○‬ ‭Preformationism‬‭:‬‭development‬‭of‬‭organisms‬‭consists‬‭of‬‭a‬‭simple‬‭enlargement‬ ‭of a body plan.‬ ‭‬ ‭Early‬ ‭1800s,‬ ‭scientists‬ ‭began‬ ‭reporting‬ ‭that‬ ‭fertilized‬ ‭eggs‬ ‭from‬ ‭hens‬ ‭and‬ ‭from‬ ‭amphibians divided repeatedly to form clusters of cells each having the same shape.‬ ‭○‬ ‭Ontogeny‬‭: the process of individual development; growing up and growing old‬ ‭‬ ‭1900:‬ ‭several‬ ‭scientists‬ ‭independently‬ ‭rediscovered‬ ‭Gregor‬ ‭Mendel’s‬ ‭1866‬ ‭paper‬ ‭demonstrating that pea plants inherit traits as discrete units.‬ ‭‬ ‭The‬ ‭fusion‬ ‭of‬ ‭Darwin’s‬ ‭theory‬ ‭of‬ ‭evolution‬ ‭by‬‭natural‬‭selection‬‭and‬‭Mendel’s‬‭laws‬‭of‬ ‭discrete‬ ‭inheritance‬ ‭became‬ ‭known‬ ‭as‬ ‭the‬ ‭modern‬ ‭synthesis‬ ‭of‬ ‭evolution‬‭,‬ ‭which‬ ‭underlies evolutionary biology today.‬ ‭‬ ‭Scientists‬ ‭would‬ ‭propose‬ ‭the‬ ‭word‬ ‭gene‬ ‭to‬ ‭describe‬‭the‬‭discrete‬‭hereditary‬‭unit‬‭that‬ ‭Mendel referred to as a “factor.”‬ ‭It would be many years before we realized that genes consist of stretches of DNA.‬ ‭Scientists‬ ‭domesticated‬ ‭a‬ ‭simple‬ ‭worm‬ ‭to‬ ‭address‬ ‭the‬ ‭question‬ ‭of‬ ‭cell‬ ‭differentiation:‬ ‭Caenorhabditis‬‭elegans‬‭.1963:‬‭Sydney‬‭Brenner‬‭decided‬‭to‬‭establish‬‭C.‬‭elegans‬‭as‬‭a‬‭model‬ ‭system‬‭, and used it to explore gene function. It is‬‭very useful because:‬ ‭‬ ‭Simple anatomy‬ ‭‬ ‭Limited number of cells‬ ‭‬ ‭Transparent embryos‬ ‭‬ ‭Genome fully sequenced‬ ‭‬ ‭Easy to maintain in the lab‬ ‭‬ ‭Easily manipulated: we can easily induce mutations‬ ‭‬ ‭Readily induce mutations‬ ‭‬ ‭Hermaphrodites: both male and female organs‬ ‭‬ ‭Life cycle: form egg to adult: 3 days (low impact on lab costs)‬ ‭‬ ‭Life span: 2-3 weeks (low impact on lab costs)‬ ‭Discoveries‬ ‭ ‬ ‭1963:‬ ‭Sydney‬ ‭Brenner‬ ‭decided‬ ‭to‬ ‭establish‬ ‭C.‬ ‭elegans‬ ‭as‬ ‭a‬ ‭model‬‭system,‬‭and‬‭used‬‭it‬‭to‬‭explore‬‭gene‬ ‭function.‬ ‭ ‬ ‭1976:‬‭John‬‭Sulston,‬‭published‬‭a‬‭complete‬‭cell‬‭lineage‬‭of‬‭C.‬‭elegans.‬‭He‬‭followed‬‭the‬‭descent‬‭of‬‭every‬‭cell‬ ‭as‬ ‭it‬ ‭divided‬ ‭and‬ ‭differentiated‬ ‭and‬ ‭found‬ ‭that‬ ‭first‬ ‭five‬ ‭cell‬ ‭divisions‬ ‭produce‬ ‭six‬ ‭founder‬ ‭cells‬ ‭that‬ ‭differentiate to ultimately give rise to all of the different tissues in the organism.‬ ‭ ‬ ‭1986: Robert Horvitz published his pioneering work on the discovery of "‬‭death genes‬‭“.‬ ‭ ‬ ‭2002:‬ ‭Sydney‬ ‭Brenner,‬ ‭John‬ ‭Sulston‬ ‭and‬ ‭Robert‬ ‭Horvitz‬ ‭shared‬ ‭the‬ ‭Nobel‬ ‭Prize‬ ‭in‬ ‭Physiology‬ ‭and‬ ‭Medicine for their seminal work done in C. elegans.‬ ‭ ‬ ‭2006:‬ ‭Andrew‬ ‭Fire‬ ‭and‬ ‭Craig‬ ‭Mello‬ ‭shared‬ ‭the‬ ‭Nobel‬ ‭Prize‬ ‭in‬ ‭Physiology‬ ‭and‬ ‭Medicine‬ ‭for‬ ‭their‬ ‭groundbreaking‬ ‭work‬ ‭on‬ ‭RNA‬ ‭interference,‬ ‭or‬ ‭RNAi,‬ ‭a‬ ‭process‬ ‭that‬ ‭results‬ ‭in‬ ‭silencing‬ ‭of‬ ‭genes‬ ‭via‬ ‭degradation of specific mRNA molecules.‬ ‭ ‬ ‭2008:‬‭Martin‬‭Chalfie‬‭received‬‭the‬‭Nobel‬‭Prize‬‭in‬‭Chemistry‬‭for‬‭showing‬‭that‬‭the‬‭Green‬‭Fluorescent‬‭Protein‬ ‭(or GFP)‬‭could be expressed in C. elegans and used‬‭as a fluorescent reporter.‬ ‭C. Elegans development‬ ‭ he‬ ‭problem‬ ‭of‬ ‭cell‬ ‭differentiation,‬ ‭seems‬ T ‭more‬‭manageable‬‭in‬‭C.elegans‬‭because‬‭the‬ ‭entire‬ ‭worm,‬ ‭with‬ ‭a‬ ‭body‬ ‭about‬‭1‬‭mm‬‭long,‬ ‭consists‬ ‭of‬ ‭just‬ ‭under‬ ‭1,000‬ ‭cells‬‭,‬ ‭all‬ ‭well‬ ‭known by scientists.‬ ‭ itotic‬ ‭lineage‬ ‭reveals‬ ‭cell‬ ‭fate‬ ‭in‬ ‭the‬ M ‭worm‬‭C.‬‭elegans.‬‭The‬‭earliest‬‭cell‬‭divisions‬ ‭in‬‭C.‬‭elegans‬‭are‬‭asymmetrical,‬‭so‬‭scientists‬ ‭could‬ ‭name‬ ‭the‬ ‭daughter‬ ‭cells‬‭produced‬‭by‬ ‭each‬‭round‬‭of‬‭mitosis,‬‭keeping‬‭track‬‭of‬‭their‬ ‭6‬ ‭NEURAL DEVELOPMENT – Prof.sse S. Bovetti – A.A 2024-2025 – anno1 semestre1 – Margherita Bosso‬ ‭ rder and “lineage,” as they descended from the fertilized egg.‬ o ‭There‬‭is‬‭a‬‭strict‬‭order‬‭of‬‭cell‬‭divisions‬‭that‬‭happens‬‭about‬‭the‬‭same‬ ‭way‬ ‭in‬ ‭every‬ ‭individual‬ ‭worm.‬ ‭You‬ ‭can‬‭make‬‭a‬‭“map”‬‭that‬‭shows‬ ‭every‬ ‭cell‬‭division‬‭that‬‭takes‬‭place‬‭in‬‭the‬‭transition‬‭from‬‭zygote‬‭to‬ ‭adult (‬‭mitotic map‬‭), and so the position of every single cell.‬ ‭The pattern of mitosis perfectly matches every cell’s fate.‬ ‭First cells:‬ ‭‬ ‭P1 = most posterior part → EMS + P2‬ ‭‬ ‭AB = most anterior part → ABa + ABp‬ ‭Experiment on‬‭C.elegans‬‭cell division:‬ ‭ he‬‭2‬‭daughter‬‭cells‬‭of‬‭the‬‭zygote‬‭were‬‭divided:‬‭AB‬‭were‬‭divided‬‭by‬‭P1‬‭and‬‭they‬‭saw‬‭that‬‭the‬‭development‬‭did‬‭not‬ T ‭change,‬ ‭so‬ ‭if‬ ‭the‬ ‭cells‬ ‭are‬ ‭divided‬‭they‬‭go‬‭on‬‭on‬‭their‬‭own‬‭path:‬‭P1‬‭divided‬‭into‬‭P2‬‭and‬‭EMS‬‭cells‬‭while‬‭Ab‬‭cell‬ ‭divided into ABa and ABp cells, so an entire organism would not develop anymore.‬ ‭So,‬‭every‬‭cell‬‭follows‬‭its‬‭particular‬‭destiny‬‭no‬‭matter‬‭what‬‭its‬‭neighboring‬‭cells‬‭are‬‭up‬‭to‬‭do‬‭:‬‭this‬‭behavior‬‭is‬‭called‬ ‭mosaic‬‭specification‬‭of‬‭cell‬‭fate‬‭→‬‭the‬‭interaction‬‭of‬‭cells‬‭is‬‭not‬‭important‬‭because‬‭the‬‭guide‬‭is‬‭inside‬‭the‬‭cells‬ ‭themself.‬ ‭This‬‭happens‬‭because‬‭P1‬‭and‬‭AB‬‭have‬‭the‬‭same‬‭mother‬‭cell‬‭but‬‭probably‬‭when‬‭they‬‭divide‬‭and‬‭the‬‭cycle‬‭ends‬‭the‬ ‭symmetrical division is not very symmetrical: different TF are released in one of the 2 parts.‬ ‭Not‬‭many‬‭factors‬‭differ‬‭from‬‭the‬‭2‬‭cells,‬‭but‬‭many‬‭important‬‭are‬‭different,‬‭for‬ ‭example‬‭skin1‬‭(SKN1).‬‭This‬‭SKN1‬‭factor‬‭is‬‭released‬‭to‬‭the‬‭P1‬‭cell‬‭and‬‭so,‬ ‭there‬ ‭is‬ ‭an‬‭asymmetrical‬‭distribution‬‭of‬‭this‬‭factor‬‭already‬‭in‬‭the‬‭mother‬ ‭cell:‬ ‭SKN1‬ ‭is‬ ‭more‬ ‭concentrated‬ ‭into‬ ‭the‬‭posterior‬‭part‬‭.‬‭Then‬‭also‬‭in‬‭P1‬ ‭cells‬‭SKN1‬‭is‬‭more‬‭concentrated‬‭in‬‭the‬‭posterior‬‭part‬‭so‬‭both‬‭the‬‭daughter‬ ‭cells would not receive SKN1, but only the posterior one, that is EMS cell.‬ ‭As‬ ‭further‬ ‭divisions‬ ‭ensue,‬ ‭each‬ ‭cell‬ ‭receives‬ ‭a‬ ‭unique‬ ‭mixture‬ ‭of‬ ‭transcription‬ ‭factors‬ ‭varying‬ ‭in‬ ‭their‬ ‭relative‬ ‭concentrations‬ ‭as‬ ‭they‬ ‭are‬ ‭parceled‬ ‭out‬ ‭among‬ ‭descendants.‬ ‭The‬ ‭particular‬ ‭composition‬ ‭of‬ ‭transcription‬ ‭factors‬ ‭each‬ ‭cell‬ ‭receives‬ ‭may‬ ‭be‬ ‭a‬ ‭result‬‭of‬‭where,‬‭exactly,‬ ‭that‬ ‭cell‬ ‭falls‬ ‭in‬ ‭the‬ ‭mitotic‬ ‭lineage.‬‭That‬‭particular‬‭mixture‬‭of‬‭transcription‬ ‭factors‬ ‭direct‬ ‭gene‬ ‭expression‬ ‭in‬ ‭the‬ ‭cell‬ ‭and‬ ‭differentiation‬‭of‬‭that‬‭cell‬‭to‬ ‭take‬‭on‬‭its‬‭fate.‬‭If‬‭the‬‭mother‬‭has‬‭no‬‭functional‬‭copies‬‭of‬‭SKN-1‬‭gene‬‭and‬ ‭cannot‬‭lay‬‭down‬‭the‬‭protein‬‭in‬‭the‬‭posterior‬‭part,‬‭none‬‭of‬‭her‬‭offspring‬‭will‬ ‭form a pharynx embryos of most species do not develop in that way!!!‬ ‭Removing‬ ‭SKN1‬ ‭the‬ ‭2‬ ‭daughter‬ ‭cells‬ ‭develop‬‭equally.‬‭Now‬‭we‬‭know‬‭that‬ ‭there‬‭are‬‭few‬‭TF‬‭activated‬‭sequentially‬‭and‬‭different‬‭gradients‬‭activate‬‭different‬‭TF‬‭,‬‭so‬‭the‬‭code‬‭of‬‭TF‬‭determines‬ ‭the complexity of each cell type.‬ ‭Most of the organisms has not a mosaic specification of cells in development.‬ ‭7‬ ‭NEURAL DEVELOPMENT – Prof.sse S. Bovetti – A.A 2024-2025 – anno1 semestre1 – Margherita Bosso‬ ‭Amphibian embryonic development‬ I‭n‬ ‭virtually‬ ‭all‬ ‭animals‬ ‭the‬ ‭first‬ ‭several‬ ‭divisions‬ ‭of‬ ‭the‬ ‭zygote‬ ‭result‬ ‭in‬ ‭a‬ ‭more‬ ‭or‬ ‭less‬ ‭spherical‬ ‭cluster‬ ‭of‬ ‭cells‬ ‭leaving a fluid filled hollow space in the center. At this stage the embryo is called‬‭blastula‬‭.‬ ‭A‬‭dimple‬‭called‬‭blastopore‬‭appears‬‭on‬‭the‬‭surface‬‭of‬‭the‬‭blastula‬‭and‬‭invades‬‭the‬‭interior‬‭of‬‭the‬‭embryo.‬‭Now‬‭the‬ ‭embryo‬‭is‬‭designed‬‭as‬‭gastrula‬‭.‬‭In‬‭amphibian‬‭gastrulation‬‭starts‬‭from‬‭the‬‭invagination‬‭of‬‭the‬‭blastula‬‭forming‬‭the‬ ‭blastopore‬‭and‬‭cells‬‭start‬‭to‬‭move‬‭in‬‭the‬‭blastopore‬‭through‬‭cell‬‭migration‬‭and‬‭divide,‬‭and‬‭a‬‭new‬‭cavity‬‭forms‬‭and‬ ‭will rise to the digestive system.‬ ‭The nervous system derives from specialized parts of ectoderm called neuroectoderm‬ ‭-‬ ‭ectoderm (‬‭blue)‬‭- most external‬ ‭-‬ ‭mesoderm (‬‭pink‬‭)‬ ‭-‬ ‭endoderm (‬‭yellow‬‭) - most internal‬ ‭The‬ ‭NS‬ ‭forms‬ ‭under‬ ‭the‬ ‭effect‬ ‭of‬ ‭notochord‬ ‭(in‬ ‭Chordates)‬‭that‬‭is‬‭a‬‭structure‬‭of‬‭the‬‭mesoderm‬‭and‬‭induce‬‭the‬ ‭ectoderm to become neuroectoderm and then NS.‬ ‭Mammalian embryonic development‬ ‭ he‬‭blastulation‬‭and‬‭gastrulation‬‭are‬‭different‬‭from‬‭the‬‭amphibian‬‭ones.‬‭The‬‭blastula‬‭is‬‭implanted‬‭in‬‭the‬‭uterus‬‭and‬ T ‭surrounded‬‭by‬‭the‬‭placenta.‬‭Mitosis‬‭and‬‭migration‬‭in‬‭the‬‭blastula‬‭forms‬‭the‬‭inner‬‭cell‬‭mass‬‭which‬‭will‬‭give‬‭rise‬‭to‬ ‭the whole body from the‬‭inner cell mass ICM‬‭,‬‭that‬‭gives rise to the entire embryo when implanted.‬ ‭A‬‭primitive‬‭streak‬‭that‬‭is‬‭the‬‭midline‬‭of‬‭the‬‭organisms:‬‭from‬‭the‬‭ICM‬‭(grey)‬‭an‬‭invagination‬‭occurs‬‭in‬‭both‬‭sides‬‭and‬ ‭cells‬ ‭migrate‬ ‭into‬ ‭the‬ ‭streak‬ ‭by‬‭moving‬‭in‬‭the‬‭internal‬‭part‬ ‭and‬‭the‬‭3‬‭layers‬‭are‬‭formed.‬ ‭At‬ ‭the‬ ‭end‬ ‭in‬ ‭the‬ ‭most‬ ‭internal‬ ‭part‬ ‭we’ll‬ ‭have‬ ‭the‬ ‭endoderm,‬ ‭mesorìdem‬ ‭and‬ ‭ectodem.‬ ‭The‬ ‭primitive‬ ‭streak‬ ‭would‬ ‭be‬ ‭crossed‬ ‭by‬ ‭cells‬ ‭that‬ ‭enter‬ ‭into‬ ‭the‬ ‭structure‬ ‭and‬ ‭go‬ ‭down‬ ‭forming the endoderm.‬ ‭The‬ ‭first‬ ‭cohort‬ ‭of‬ ‭cells‬ ‭will‬ ‭give‬ ‭rise‬ ‭to‬ ‭endoderm‬‭.‬ ‭The‬ ‭later‬ ‭arriving‬ ‭cells‬‭will‬‭fill‬‭the‬ ‭surface‬ ‭between‬ ‭the‬ ‭outer‬ ‭layer‬ ‭and‬ ‭the‬ ‭endoderm‬ ‭forming‬‭mesoderm‬‭.‬ ‭Gastrulation‬ ‭begins‬ ‭when‬ ‭the‬ ‭inner‬ ‭cell‬ ‭mass‬ ‭form‬ ‭a‬ ‭disc‬ ‭two‬ ‭cell‬ ‭layers‬ ‭thick‬ ‭inside the embryo‬ ‭Cells on the upper surface migrate toward the center forming a crease called primitive streak (midline of the animal)‬ ‭In‬‭vertebrate‬‭embryos,‬‭the‬‭primitive‬‭streak‬‭marks‬‭the‬‭midline‬‭position,‬‭where‬‭the‬‭nervous‬‭system‬‭will‬‭develop‬‭in‬‭the‬ ‭ectoderm.‬‭The‬‭crease‬‭formed‬‭by‬‭the‬‭primitive‬‭streak‬‭is‬‭more‬‭pronounced‬‭at‬‭one‬‭end,‬‭called‬‭the‬‭node‬‭and‬‭it‬‭marks‬ ‭where the animal’s brain and head will form.‬ ‭8‬ ‭NEURAL DEVELOPMENT – Prof.sse S. Bovetti – A.A 2024-2025 – anno1 semestre1 – Margherita Bosso‬ ‭ he‬‭nervous‬‭system‬‭begins‬‭as‬‭an‬‭elongated‬‭layer‬ T ‭of‬ ‭ectodermal‬ ‭cells‬ ‭on‬ ‭the‬ ‭surface,‬ ‭called‬ ‭the‬ ‭neural plate‬‭.‬ ‭As‬ ‭cell‬ ‭divisions‬ ‭and‬ ‭migrations‬ ‭continue,‬ ‭the‬ ‭sides‬ ‭of‬‭the‬‭neural‬‭plate‬‭rise‬‭up‬‭to‬‭form‬‭the‬‭walls‬ ‭of‬‭a‬‭neural‬‭groove.‬‭These‬‭walls‬‭meet‬‭and‬‭fuse‬‭at‬ ‭the midline to form a‬‭neural tube‬‭=‬‭neurulation‬‭.‬ ‭The‬ ‭rest‬ ‭of‬ ‭the‬ ‭nervous‬ ‭system‬ ‭will‬ ‭arise‬ ‭from‬ ‭a‬ ‭group‬ ‭of‬ ‭ectodermal‬ ‭cells‬ ‭that‬ ‭were‬ ‭at‬‭the‬‭peaks‬ ‭of‬ ‭the‬ ‭two‬ ‭sides‬ ‭of‬ ‭the‬ ‭neural‬ ‭groove‬ ‭that‬‭where‬ ‭not‬ ‭included‬ ‭into‬ ‭the‬ ‭neural‬ ‭tube,‬ ‭called‬ ‭neural‬ ‭crest‬ ‭cells‬‭,‬ ‭that‬ ‭will‬ ‭migrate‬ ‭in‬ ‭different‬ ‭parts‬ ‭of‬ ‭the‬‭body‬‭in‬‭very‬‭important‬‭structures‬‭and‬‭will‬‭give‬ ‭rise to the peripheral nervous system.‬ ‭NEURULATION: process by which a gastrula transforms into a neurula‬ ‭←‬‭see video‬ ‭The neural plate and neural tube‬ ‭9‬ ‭NEURAL DEVELOPMENT – Prof.sse S. Bovetti – A.A 2024-2025 – anno1 semestre1 – Margherita Bosso‬ ‭ s‬‭development‬‭proceeds‬‭there‬‭will‬‭be‬‭the‬‭formation‬‭of‬‭vesicles:‬‭the‬‭primary‬‭vesicle‬‭during‬‭development‬‭will‬‭give‬ A ‭rise to secondary vesicles.‬‭Primary vesicles‬‭are:‬ ‭-‬ ‭the FOREBRAIN (PROSENCEPHALON) - most anterior,‬ ‭-‬ ‭the MIDBRAIN (MESENCEPHALON) and‬ ‭-‬ ‭the HINDBRAIN (RHOMBENCEPHALON)‬ ‭and the‬‭secondary vesicles‬‭are:‬ ‭-‬ ‭the TELENCEPHALON and DIENCEPHALON (from the forebrain),‬ ‭-‬ ‭the MESENCEPHALON (from the midbrain)‬ ‭-‬ ‭the METENCEPHALON and the MYELENCEPHALON (from the hindbrain)‬ ‭As the system is mature these structures will give rise to correspondent adult derivatives (‬‭see upper‬‭table‬‭)‬ ‭Neural tube defects‬ ‭ nencephaly‬‭:‬‭cranial‬‭neural‬‭folds‬‭do‬‭not‬‭fuse‬‭in‬‭the‬‭developing‬‭embryo‬‭in‬ A ‭the‬ ‭anterior‬ ‭part‬ ‭and‬ ‭most‬ ‭or‬ ‭all‬ ‭of‬ ‭the‬ ‭brain‬ ‭is‬ ‭missing‬ ‭(usually‬ ‭not‬ ‭compatible with life)‬ ‭Spina‬ ‭bifida‬‭:‬ ‭failure‬ ‭of‬ ‭the‬ ‭neural‬ ‭tube‬ ‭to‬ ‭fuse‬ ‭at‬ ‭its‬ ‭posterior‬ ‭end,‬ ‭resulting‬‭in‬‭either‬‭an‬‭open‬‭lesion‬‭on‬‭the‬‭spine,‬‭with‬‭significant‬‭damage‬‭to‬ ‭the nerves and spinal cord.‬ ‭Ectodermal contributions to the body:‬ ‭Demonstrating self-regulation in embryos‬ ‭To‬‭understand‬‭the‬‭mechanisms‬‭of‬‭neurulation,‬‭we‬‭need‬‭to‬‭return‬‭to‬‭the‬‭work‬‭of‬‭early‬‭embryologists‬‭and‬‭understand‬ t‭he concept of “self-regulation”‬ ‭10‬ ‭NEURAL DEVELOPMENT – Prof.sse S. Bovetti – A.A 2024-2025 – anno1 semestre1 – Margherita Bosso‬ ‭1891 - Driesch‬ ‭ e‬‭used‬‭a‬‭hydra‬‭(simple‬‭organism)‬‭to‬‭study‬‭development:‬‭he‬‭separated‬‭the‬‭4‬‭cells‬‭that‬‭normally‬‭would‬‭make‬‭one‬ H ‭larva.‬‭From‬‭each‬‭cells‬‭4‬‭almost‬‭complete‬‭hydra‬‭developed,‬‭even‬‭if‬‭they‬‭were‬‭smaller‬‭and‬‭different‬‭in‬‭size‬‭from‬‭the‬ ‭“original” one. Entirely give rise to whole individuals so are 4 totipotent stem cells.‬ ‭1903 - Spemann‬ ‭He‬‭used‬‭an‬‭amphibian‬‭and‬‭took‬‭from‬‭the‬‭embryo‬‭divided‬‭the‬‭blastula‬‭in‬‭2‬‭parts:‬‭if‬‭1‬‭nucleus‬‭migrates‬‭into‬‭one‬‭of‬ t‭he two portions, it brought to the formation of 2 entire organisms.‬ ‭1903 - Weismann‬ ‭He‬ ‭removed‬‭a‬‭part‬‭of‬‭the‬‭blastula‬‭and‬‭saw‬‭that‬‭the‬‭organism‬‭develop‬‭onrmally‬‭because‬‭the‬‭blastula‬‭can‬‭recover‬ t‭he damage and give rise to an entire organism.‬ ‭ hese‬‭experiments‬‭brought‬‭to‬‭the‬‭concept‬‭of‬‭Self-regulation‬‭:‬‭process‬‭by‬‭which‬‭embryos‬‭manage‬‭to‬‭compensate‬ T ‭for‬ ‭missing‬ ‭or‬ ‭damaged‬ ‭cells‬‭and‬‭nevertheless‬‭produce‬‭an‬‭entire‬‭individual‬‭→‬‭conditional‬‭specification‬‭of‬‭cell‬ ‭fate‬‭, because this process depends on cell-cell interaction‬ ‭C.‬ ‭Elegans‬ ‭→‬ ‭Mosaic‬ ‭specification‬ ‭of‬ ‭cell‬ ‭fate‬ ‭→‬ ‭Fate‬ ‭predestined‬ ‭by‬ ‭its‬ ‭mitotic‬ ‭lineage,‬ ‭no‬ ‭matter‬ ‭what‬ ‭ eighboring cells do - NO INDUCTION PROCESS‬ n ‭Cell fate depends on environmental conditions.‬ ‭Other‬‭animals‬‭→‬‭Fate‬‭predestined‬‭by‬‭its‬‭mitotic‬‭lineage,‬‭no‬‭matter‬‭what‬‭neighboring‬‭cells‬‭do‬‭→‬‭Cells‬‭take‬‭on‬‭a‬‭fate‬ ‭that‬ ‭is‬ ‭appropriate‬ ‭for‬ ‭their‬ ‭location‬ ‭in‬ ‭the‬ ‭body,‬ ‭which‬ ‭is‬ ‭determined‬ ‭by‬ ‭the‬‭type‬‭of‬‭cells‬‭that‬‭surround‬‭them.‬‭In‬ ‭other‬ ‭words,‬ ‭cellular‬ ‭differentiation‬ ‭is‬ ‭guided‬ ‭by‬ ‭cell-cell‬ ‭interactions,‬ ‭the‬ ‭communication‬ ‭and‬ ‭influence‬ ‭between‬ ‭developing cells: INDUCTION‬ ‭Spemann (optic cup)‬ ‭ he optic cup induces the epithelium to form a lens:‬ T ‭Induction‬‭:‬ ‭The‬ ‭process‬‭by‬‭which‬‭one‬‭group‬‭of‬‭cells‬ ‭directs the differentiation of other, nearby cells.‬ ‭Hans‬‭Spemann‬‭(1900)‬‭noted‬‭that‬‭the‬‭vertebrate‬‭eye‬ ‭develops‬ ‭when‬ ‭the‬ ‭neural‬ ‭tube‬ ‭extends‬ ‭two‬ ‭optic‬ ‭cups‬‭,‬ ‭out‬ ‭to‬ ‭the‬ ‭epithelium.‬ ‭The‬ ‭optic‬ ‭cup‬ ‭will‬ ‭develop‬‭the‬‭retina‬‭,‬‭while‬‭the‬‭overlying‬‭epithelium‬‭will‬ ‭produce the transparent lens and cornea.‬ ‭He‬‭tried‬‭to‬‭implant‬‭the‬‭optic‬‭cup‬‭in‬‭a‬‭different‬‭location‬ ‭and‬ ‭a‬ ‭correspondent‬ ‭retina‬ ‭developed,‬ ‭but‬ ‭this‬ ‭not‬ ‭happened‬‭when‬‭the‬‭site‬‭of‬‭transplantation‬‭of‬‭the‬‭optic‬‭cup‬‭was‬‭too‬‭far‬‭away‬‭from‬‭the‬‭normal‬‭point‬‭of‬‭formation.‬‭He‬ ‭discovered‬ ‭that‬ ‭the‬ ‭graft‬ ‭of‬ ‭lens‬ ‭can‬ ‭send‬ ‭signals‬ ‭so‬‭it‬‭is‬‭an‬‭INDUCTIVE‬‭PROCESS,‬‭so‬‭there‬‭is‬‭a‬‭factor‬‭that‬‭is‬ ‭released‬‭and‬‭has‬‭to‬‭reach‬‭a‬‭receptor‬‭to‬‭have‬‭a‬‭consequence,‬‭so‬‭also‬‭COMPETENCE‬‭is‬‭important.‬‭In‬‭the‬‭posterior‬ ‭part the graft of the optic cup does not have consequences because here there are not receptors.‬ ‭Anchor point (Spemann and Mangold)‬ ‭ ans‬‭Spemann‬‭and‬‭Hilde‬‭Mangold‬‭(1924)‬‭began‬‭transplanting‬‭portions‬‭of‬ H ‭one‬ ‭blastula‬ ‭into‬ ‭other‬ ‭blastulas.‬ ‭IN‬ ‭one‬ ‭of‬ ‭their‬ ‭experiments‬ ‭they‬ ‭transplanted‬‭a‬‭specific‬‭part‬‭that‬‭is‬‭the‬‭dorsal‬‭lip‬‭and‬‭in‬‭this‬‭case‬‭it‬‭not‬‭only‬ ‭induced‬ ‭the‬ ‭formation‬ ‭of‬ ‭some‬ ‭structures,‬ ‭it‬ ‭seemed‬ ‭to‬ ‭induce‬ ‭the‬ ‭formation‬ ‭of‬ ‭an‬ ‭entirely‬ ‭new‬ ‭individual,‬ ‭with‬ ‭a‬ ‭head‬‭and‬‭central‬‭nervous‬ ‭system: the‬‭dorsal lip is the ORGANIZER.‬ ‭Cells‬ ‭in‬ ‭the‬ ‭early‬ ‭embryo‬ ‭that‬ ‭would‬ ‭eventually‬ ‭form‬ ‭the‬ ‭skin‬ ‭can‬ ‭be‬ ‭induced‬ ‭to‬ ‭change‬ ‭their‬ ‭fates.‬ ‭These‬ ‭cells‬ ‭must‬ ‭retain‬ ‭the‬ ‭ability,‬ ‭or‬ ‭competence, to adopt other fates.‬ ‭In‬ ‭another‬ ‭experiment‬ ‭the‬ ‭dorsal‬ ‭lip‬ ‭of‬ ‭the‬ ‭blastopore‬ ‭was‬ ‭transplanted‬ ‭from‬ ‭a‬ ‭donor‬ ‭blastula‬ ‭to‬ ‭a‬ ‭receiving‬ ‭blastula‬ ‭and‬ ‭a‬ ‭new‬ ‭NS‬ ‭developed:‬ ‭they‬ ‭transplanted‬ ‭a‬ ‭specific‬ ‭region‬ ‭that‬ ‭is‬‭the‬‭ORGANIZER‬‭that‬‭induces‬ ‭the development of NS despite epithelium.‬ ‭The‬ ‭transplanted‬ ‭dorsal‬ ‭lip‬ ‭not‬ ‭only‬ ‭induced‬ ‭the‬ ‭formation‬ ‭of‬ ‭some‬ ‭structures,‬‭it‬‭seemed‬‭to‬‭induce‬‭the‬‭formation‬‭of‬‭an‬‭entirely‬‭new‬‭individual,‬ ‭with‬‭a‬‭head‬‭and‬‭central‬‭nervous‬‭system.‬‭It‬‭would‬‭be‬‭over‬‭50‬‭years‬‭before‬ ‭any‬ ‭techniques‬ ‭would‬ ‭be‬ ‭available‬ ‭to‬ ‭isolate‬ ‭and‬ ‭identify‬ ‭the‬ ‭particular‬ ‭11‬ ‭NEURAL DEVELOPMENT – Prof.sse S. Bovetti – A.A 2024-2025 – anno1 semestre1 – Margherita Bosso‬ ‭molecule(s) from the dorsal lip of the blastopore that organizes a new individual.‬ ‭Identifying molecules that mediate neural induction‬ ‭ he discovery of the‬‭default model‬‭: 2 experiments were performed:‬ T ‭1- Animal caps dissected and cultured intact without dissociation → epidermis.‬ ‭2- Animal caps cells are separated from each other → neural cells‬ ‭Dissociation‬ ‭allowed‬ ‭molecules‬ ‭that‬ ‭prevent‬ ‭neural‬ ‭induction‬ ‭to‬ ‭escape‬‭from‬ ‭around‬ ‭the‬ ‭animal‬ ‭cap‬ ‭cells‬ ‭into‬ ‭the‬ ‭surrounding‬ ‭fluid,‬ ‭thereby‬ ‭reducing‬ ‭the‬ ‭concentration‬ ‭of‬ ‭those‬ ‭blocking‬ ‭molecules‬ ‭and‬ ‭allowing‬ ‭the‬ ‭cells‬ ‭to‬ ‭adopt‬ ‭a‬ ‭neural fate by default‬‭.‬ ‭The‬ ‭molecules‬ ‭preventing‬ ‭neural‬ ‭induction‬ ‭are‬ ‭called‬ ‭members‬ ‭of‬ ‭Bone‬ ‭morphogenetic‬‭proteins‬‭family‬‭(BMP2,‬‭BMP4,‬‭BMP7)‬‭and‬‭were‬‭found‬‭in‬‭the‬ ‭animal‬ ‭cap‬ ‭of‬ ‭the‬ ‭blastula:‬ ‭to‬ ‭confirm‬ ‭that‬‭these‬‭molecules‬‭were‬‭responsible‬ ‭for‬ ‭the‬ ‭inhibition‬ ‭of‬ ‭neural‬ ‭development‬ ‭dissociated‬ ‭cell‬ ‭were‬ ‭cultured‬ ‭with‬ ‭BMP and they brought to the formation of epidermis, as in case1.‬ ‭The‬ ‭organizer‬ ‭might‬ ‭promote‬ ‭neural‬ ‭induction‬ ‭because‬ ‭it‬ ‭produces‬ ‭molecules‬ ‭that‬ ‭inhibit‬ ‭BMPs‬ ‭in‬ ‭the‬ ‭animal‬ ‭cap,‬ ‭preventing‬ ‭its‬ ‭cells‬ ‭from‬ ‭acquiring an epidermal fate.‬ ‭What are the active molecules produced by the organizer to induce neural tissue?‬ ‭Signals from the organizer‬ ‭ hen the experiment was repeated in amphibians‬ T ‭2 models:‬ ‭-‬ ‭the‬ ‭exposure‬ ‭to‬ ‭LiCl‬ ‭will‬ ‭give‬ ‭rise‬ ‭to‬ ‭an‬ ‭amphibian‬ ‭with‬ ‭an‬ ‭enormous‬ ‭head.‬ ‭Here‬ ‭they‬ ‭supposed‬ ‭to‬ ‭have‬ ‭a‬ ‭major‬ ‭concentration of BMP‬ ‭-‬ ‭the exposure to UV will give rise to an amphibian without head‬ ‭So‬‭they‬‭took‬‭an‬‭amphibian‬‭blastula‬‭and‬‭exposed‬‭it‬‭to‬‭LiCl‬‭to‬‭increase‬ ‭the‬ ‭concentration‬ ‭of‬ ‭BMPs‬ ‭near‬ ‭the‬ ‭blastopore‬ ‭near‬ ‭the‬‭portion‬‭that‬ ‭will‬‭form‬‭the‬‭NS‬‭and‬‭then‬‭they‬‭extracted‬‭mRNA‬‭from‬‭these‬‭cells‬‭and‬‭injected‬‭it‬‭into‬‭a‬‭blastula‬‭that‬‭was‬‭irradiated‬ ‭with‬ ‭UV.‬ ‭They‬ ‭saw‬ ‭that‬ ‭doing‬ ‭this‬ ‭there‬ ‭was‬ ‭a‬ ‭recovery‬ ‭of‬ ‭the‬ ‭UV-irradiated‬ ‭embryo‬ ‭that‬ ‭developed‬ ‭a‬ ‭nervous‬ ‭system. (A)‬ ‭ hen‬ ‭they‬ ‭took‬ ‭the‬ ‭normal‬ ‭amphibian‬ ‭embryo‬ ‭and‬ ‭extracted‬ ‭mRNA‬ ‭from‬ ‭the‬ ‭dorsal‬ ‭lip‬ ‭of‬ ‭the‬ ‭blastopore,‬ T ‭sequenced‬‭it‬‭creating‬‭a‬‭sequencing‬‭cDNA‬‭library‬‭and‬‭injected‬‭single‬‭mRNAs‬‭in‬‭many‬‭UV-irradiated‬‭blastulas.‬‭They‬ ‭discovered that by injecting isolated‬‭Nogging‬‭mRNA‬‭the phenotype was entirely rescued.‬ ‭ o, some mRNA was able to recover, such as Nogging and other mRNAs.‬ S ‭They‬ ‭also‬ ‭discovered‬ ‭that‬ ‭concentration‬ ‭is‬ ‭fondamental‬‭:‬ ‭by‬ ‭injecting‬ ‭no‬ ‭Noggin‬ ‭or‬ ‭just‬ ‭a‬ ‭few‬ ‭there‬ ‭is‬ ‭no‬ ‭recovery‬ ‭and‬ ‭injecting‬ ‭too‬ ‭much‬ ‭Nogging‬ ‭there‬‭is‬‭no‬‭recovery‬‭so‬‭the‬‭exact‬‭concentration‬‭is‬‭important.‬‭Noggin‬‭works‬‭in‬ ‭a concentration dependent manner.‬ ‭12‬ ‭NEURAL DEVELOPMENT – Prof.sse S. Bovetti – A.A 2024-2025 – anno1 semestre1 – Margherita Bosso‬ ‭ fter‬‭Noggin‬‭other‬‭molecules‬‭were‬‭isolated,‬‭such‬‭as‬‭Chordin‬‭and‬‭Follistatin‬‭,‬‭that‬‭were‬‭found‬‭to‬‭be‬‭expressed‬‭in‬ A ‭the dorsal lip of the blastopore. These molecules were discovered by knockout experiments.‬ ‭Homologues of these genes were promptly found in mammals.‬ ‭All use the same basic mechanism to induce ectoderm to form the nervous system‬ ‭What organizes the organizer?‬ ‭How‬ ‭did‬ ‭the‬ ‭dorsal‬ ‭lip‬ ‭of‬ ‭the‬ ‭blastopore‬ ‭come‬ ‭to‬ ‭express‬ ‭the‬ ‭ rganizer signals?‬ o ‭1.‬ ‭Endoderm‬ ‭induces‬ ‭the‬ ‭cells‬ ‭in‬ ‭the‬ ‭dorsal‬ ‭lip‬ ‭of‬ ‭the‬ ‭blastopore‬ ‭(the‬ ‭presumptive‬ ‭chordo-mesorderm)‬ ‭to‬ ‭start‬ ‭expressing organizer signal genes‬ ‭2.‬ ‭The‬ ‭protein‬ ‭that‬ ‭endodermal‬ ‭cells‬ ‭secrete‬ ‭to‬ ‭induce‬ ‭the‬ ‭dorsal‬ ‭lip‬ ‭of‬ ‭the‬ ‭blastopore‬ ‭to‬ ‭start‬ ‭making‬ ‭organizers‬ ‭is‬ ‭called‬‭β-catenin.‬ ‭The‬ ‭mother‬ ‭strategically‬ ‭placed‬ ‭mRNAs‬ ‭and‬ ‭proteins‬ ‭in‬ ‭the‬ ‭egg‬ ‭cytoplasm‬ ‭so‬ ‭that‬ ‭β-catenin‬ ‭would‬ ‭be‬ ‭concentrated‬ ‭in‬ ‭the‬ ‭right‬ ‭place‬ ‭in‬ ‭the‬ ‭endoderm.‬ ‭β-catenins‬ ‭released‬ ‭from‬ ‭the‬‭mother‬‭cell‬ ‭so‬ ‭mRNAs‬ ‭are‬ ‭asymmetrically‬ ‭organized‬ ‭in‬ ‭the‬ ‭cells‬ ‭during‬ ‭development, inducing the ventral or dorsal fate.‬ ‭Chain‬ ‭of‬ ‭inductive‬ ‭events‬ ‭that‬ ‭are‬ ‭needed‬ ‭to‬ ‭make‬ ‭a‬ ‭really‬ ‭complicated‬ ‭metazoan.‬ ‭One‬ ‭advantage‬ ‭of‬ ‭having‬ ‭many‬ ‭different‬ ‭inductive‬ ‭steps‬ ‭is‬ ‭that‬ ‭if‬ ‭a‬ ‭chunk‬ ‭of‬ ‭embryo‬ ‭is‬ ‭removed‬ ‭or‬ ‭damaged,‬ ‭the‬ ‭embryo‬ ‭will‬ ‭self-regulate‬ ‭in‬ ‭compensation,‬ ‭and‬ ‭you’ll‬ ‭still‬ ‭end‬ ‭up‬ ‭with‬ ‭a‬ ‭complete‬ ‭individual.‬ ‭Mechanisms on BMP working‬ ‭ he‬ ‭cell‬ ‭expressing‬ ‭the‬ ‭receptor‬ ‭for‬ T ‭BMPs,‬ ‭and‬ ‭when‬ ‭BMP‬ ‭binds‬ ‭the‬ ‭receptor,‬‭that‬‭cell‬‭becomes‬‭an‬‭epidermal‬ ‭cell.‬ ‭Having‬ ‭Nogging,‬ ‭Chordin‬ ‭or‬ ‭Follistatin,‬‭the‬‭receptor‬‭is‬‭blocked‬‭by‬‭this‬ ‭antagonist,‬ ‭so‬ ‭BMP‬ ‭can’t‬ ‭ligate‬ ‭the‬ ‭receptor‬ ‭and‬ ‭this‬ ‭cell‬ ‭will‬ ‭become‬ ‭neuron.‬ ‭BMPs‬ ‭prevent‬ ‭the‬ ‭induction‬ ‭of‬ ‭the‬ ‭neural‬ ‭fate‬ ‭inducing‬ ‭the‬ ‭non-neural‬ ‭development.‬‭If‬‭BMPs‬‭can’t‬‭bind,‬‭the‬‭cell‬ ‭goes through neuronal development.‬ ‭Other‬ ‭signals‬ ‭are‬ ‭released‬ ‭from‬ ‭the‬ ‭notochord‬‭and‬‭are‬‭very‬‭important‬‭for‬‭the‬ ‭development‬ ‭of‬ ‭the‬ ‭dorso-ventral‬ ‭axis!‬ ‭(next lesson…)‬ ‭13‬ ‭NEURAL DEVELOPMENT – Prof.sse S. Bovetti – A.A 2024-2025 – anno1 semestre1 – Margherita Bosso‬ ‭Summary - lesson1‬ ‭‬ I‭n‬‭C.elegans‬‭,‬‭cell‬‭division‬‭allocates‬‭the‬‭transcription‬‭factors‬‭that‬‭were‬‭unevenly‬‭distributed‬‭in‬‭the‬‭egg‬‭and‬ ‭consequently‬‭each‬‭resulting‬‭cell‬‭has‬‭a‬‭unique‬‭mix‬‭of‬‭transcription‬‭factors:‬‭mosaic‬‭specification‬‭of‬‭cell‬‭fate,‬ ‭according to which every cell follows its particular destiny no matter what its neighboring cells are;‬ ‭‬ ‭In‬‭other‬‭species,‬‭this‬‭mosaic‬‭specification‬‭of‬‭cell‬‭fate‬‭has‬‭been‬‭supplanted‬‭by‬‭conditional‬‭specification‬‭of‬ ‭cell fate‬‭through‬‭cell-cell interactions‬‭and signals‬‭released by the neighbouring cells;‬ ‭‬ ‭In vertebrates, maternal factors trigger a chain of events to form the nervous system:‬ ‭○‬ ‭accumulation of β-catenin in blastomeres that will become the endoderm;‬ ‭○‬ ‭The‬‭β-catenin‬‭causes‬‭the‬‭cells‬‭that‬‭will‬‭form‬‭the‬‭dorsal‬‭lip‬‭of‬‭the‬‭blastopore‬‭to‬‭secrete‬‭organizing‬ ‭proteins such as noggin and chordin;‬ ‭○‬ ‭These‬ ‭mesodermal‬ ‭organizers‬ ‭block‬ ‭BMP‬‭signaling‬‭in‬ ‭the‬ ‭overlying‬ ‭ectoderm‬ ‭to‬ ‭induce‬ ‭those‬ ‭cells‬ ‭to‬ ‭switch‬ ‭fates‬ ‭from‬ ‭epidermal‬ ‭cells‬ ‭to‬ ‭neural‬ ‭cells,‬ ‭forming‬ ‭the‬ ‭neural‬ ‭tube.‬ ‭The‬ ‭organizer‬ ‭cells‬ ‭migrate‬ ‭to‬ ‭become‬ ‭mesoderm and, eventually, the notochord.‬ ‭Lesson2 - 14.11 (Prof.ssa Bovetti)‬ ‭DEVELOPMENT OF A BODY PATTERN‬ ‭ nce‬‭the‬‭neuroectoderm‬‭has‬‭been‬‭established,‬‭the‬‭next‬‭step‬‭in‬‭neural‬‭development‬‭is‬‭to‬‭divide‬‭it‬‭up‬‭into‬‭areas‬‭that‬ O ‭will‬‭lay‬‭the‬‭basis‬‭for‬‭regional‬‭specializations‬‭in‬‭the‬‭structure‬‭of‬‭the‬‭mature‬‭nervous‬‭system.‬‭This‬‭process‬‭is‬‭known‬ ‭as‬‭patterning‬‭.‬ ‭PATTERNING OF THE NEUROECTODERM‬ ‭In‬ ‭both‬ ‭Drosophila‬ ‭and‬ ‭vertebrates,‬ ‭patterning‬‭the‬‭nervous‬‭system‬‭involves‬‭subdivisions‬‭in‬‭the‬‭two‬ ‭ xes of the neuroectoderm: anteroposterior and dorsoventral axis‬‭(see picture)‬‭.‬ a ‭In‬ ‭the‬ ‭dorsal‬ ‭part‬ ‭of‬ ‭the‬ ‭gastrula‬ ‭the‬ ‭neural‬ ‭ectoderm‬ ‭and‬ ‭neural‬ ‭plate‬ ‭forms‬ ‭under‬ ‭the‬ ‭releasing‬ ‭of‬ ‭specific‬ ‭molecules‬‭by‬‭the‬‭notochord.‬‭The‬‭midline‬‭is‬‭important‬‭because‬‭it‬‭is‬‭the‬‭first‬‭indicator‬‭of‬‭the‬‭body‬‭plan:‬‭in‬‭the‬‭midline‬ ‭the‬‭neural‬‭tube‬‭forms.‬‭Then‬‭we‬‭can‬‭distinguish‬‭the‬‭antero‬‭posterior‬‭axis‬‭and‬‭when‬‭the‬‭neural‬‭tube‬‭closes‬‭we‬‭can‬ ‭identify a dorso-ventral orientation.‬ ‭The‬ ‭dorsal‬ ‭portion‬ ‭would‬ ‭be‬ ‭in‬ ‭the‬ ‭opposite‬ ‭part‬ ‭from‬ ‭the‬ ‭midline.‬ ‭In‬ ‭the‬ ‭dorsal‬ ‭part‬ ‭the‬ ‭brain‬‭develops‬‭and‬‭there‬‭will‬‭be‬‭different‬ ‭structures‬ ‭according‬ ‭to‬ ‭the‬ ‭expression‬ ‭of‬ ‭different‬ ‭genes.‬ ‭As‬ ‭development‬ ‭proceed‬ ‭morphological‬ ‭changes‬ ‭became‬ ‭evident:‬ ‭from‬ ‭anterior‬ ‭to‬ ‭posterior‬ ‭there‬ ‭will‬ ‭be‬ ‭the‬ ‭forebrain,‬ ‭the‬ ‭midbrain, the hindbrain ad finally the spinal chord.‬ ‭In‬‭the‬‭image‬‭we‬‭see‬‭the‬‭formation‬‭of‬‭the‬‭neurosystem‬‭in‬‭insects‬ ‭(‭D ‬ rosophila).‬ ‭Development in Drosophila‬ ‭ he‬ ‭Drosophila‬ ‭gene‬ ‭decapentaplegic‬ ‭(dpp)‬ ‭encodes‬ ‭a‬ ‭homologue‬ ‭of‬ ‭vertebrate‬ ‭BMP2‬ ‭and‬ ‭BMP4.‬ ‭The‬ ‭gene‬ T ‭encoding vertebrate chordin is homologous to the Drosophila gene short gastrulation (sog)‬ ‭Neuroectoderm → ventral portion‬ ‭14‬ ‭NEURAL DEVELOPMENT – Prof.sse S. Bovetti – A.A 2024-2025 – anno1 semestre1 – Margherita Bosso‬ ‭ he‬‭dark‬‭grey‬‭is‬‭ventral‬‭positioned‬‭and‬‭light‬‭grey‬‭is‬‭dorsal‬‭position‬‭and‬‭represents‬‭the‬‭gradient‬‭of‬‭the‬‭expression‬‭of‬ T ‭Dorsal.‬‭Dots‬‭are different cells.‬ ‭Dorsal‬‭activate‬‭Snail‬‭gene‬‭(ventral)‬‭and‬‭in‬‭the‬‭dorsal‬‭part‬‭activate‬‭DPP‬‭,‬‭while‬‭in‬‭the‬‭medial‬‭part‬‭activates‬‭Sog‬‭so‬ ‭depending‬ ‭on‬ ‭the‬ ‭concentration‬ ‭of‬ ‭dorsal‬ ‭different‬ ‭genes‬ ‭are‬ ‭activated.‬ ‭The‬ ‭most‬ ‭dorsal‬ ‭portion‬ ‭and‬ ‭the‬‭lateral‬ ‭portion are separated because of the antagonist mechanism between DPP and Sog.‬ ‭These‬‭genes‬‭interact‬‭with‬‭each‬‭other:‬‭Snail‬‭repress‬‭the‬‭action‬‭of‬‭Sog‬‭and‬‭sog‬‭repress‬‭the‬‭action‬‭of‬‭DPP‬‭and‬‭vice‬ ‭versa‬‭.‬‭This‬‭repression‬‭makes‬‭that‬‭these‬‭genes‬‭are‬‭expressed‬‭in‬‭some‬‭portions.‬‭The‬‭most‬‭ventral‬‭part‬‭(mesoderm‬ ‭in violet).‬ ‭The‬‭mesoderm‬‭goes‬‭inside‬‭and‬‭the‬‭2‬‭pieces‬‭of‬‭the‬‭ectoderm‬‭join‬‭in‬‭the‬‭middle‬‭part‬‭and‬‭going‬‭inside‬‭the‬‭2‬‭lateral‬ ‭portions‬ ‭start‬ ‭to‬‭touch‬‭each‬‭other‬‭and‬‭these‬‭will‬‭became‬‭the‬‭neuroectoderm‬‭(in‬‭Drosophila‬‭the‬‭neural‬‭tube‬‭is‬‭not‬ ‭present).‬ ‭Then‬‭there‬‭will‬‭be‬‭the‬‭delamination‬‭process‬‭in‬‭which‬‭proliferation‬‭of‬‭cells‬‭brings‬‭to‬‭the‬‭formation‬‭of‬‭different‬‭layers:‬ ‭different layers of cells will give rise to a specific cells type of nervous system.‬ ‭Patterns of gene expression are set-up by morphogens‬ ‭ atterning‬ ‭involves‬ ‭long‐range‬ ‭signalling‬ ‭that‬ ‭provides‬ ‭cells‬ ‭with‬ P ‭information‬‭about‬‭their‬‭location‬‭within‬‭the‬‭neural‬‭epithelium:‬‭POSITIONAL‬ ‭information.‬ ‭Blue‬ ‭cells‬ ‭are‬ ‭sense‬ ‭high‬ ‭concentrations‬ ‭of‬ ‭the‬ ‭signal‬ ‭while‬ ‭red‬ ‭cells‬ ‭sense lower concentration of the signal.‬ ‭Organizer‬‭:‬‭the‬‭signalling‬‭source‬‭(signalling‬‭centre),‬‭release‬‭the‬‭signalling‬ ‭molecules forming a gradient‬ ‭Morphogen‬‭:‬ ‭A‬ ‭diffusible‬ ‭signal‬ ‭that‬ ‭provokes‬ ‭more‬ ‭than‬ ‭one‬ ‭cellular‬ ‭response depending on its concentration around the cell‬ ‭The‬ ‭response‬ ‭of‬ ‭a‬ ‭cell‬ ‭reflects‬ ‭its‬ ‭distance‬ ‭from‬ ‭the‬ ‭source‬ ‭and‬ ‭its‬ ‭response according to a specific concentration of the morphogen.‬ ‭The‬ ‭cellular‬ ‭response‬ ‭to‬ ‭a‬ ‭morphogen‬ ‭is‬ ‭usually‬ ‭not‬‭the‬‭acquisition‬‭of‬‭a‬‭specific‬‭cell‬‭fate‬‭but‬‭the‬‭expression‬‭of‬ ‭specific transcription factors‬‭in domains within the epithelium.‬ ‭TFs influence cell behaviour or fates through affecting the expression of other genes.‬ ‭This process is very long and‬‭gradually gives rise to the specific cell type‬‭.‬ ‭Which‬‭are‬‭the‬‭mechanisms‬‭that‬‭typically‬‭organize‬‭a‬‭body‬‭plan‬‭including‬‭brain‬‭regions?‬‭Our‬‭best‬‭understanding‬‭of‬ ‭subsequent events comes from work in fruit flies (Drosophila Melanogaster), because:‬ ‭-‬ ‭Easy to grow → advanced genetics and molecular tools‬ ‭-‬ ‭Life cycle: about 10 days at 25°C (from fertilization to adult age)‬ ‭-‬ ‭embryo development about 24 hours 3 instar‬ ‭-‬ ‭stages sexual maturity reached in 12 hours‬ ‭-‬ ‭Life Span: 60 - 80 days‬ ‭-‬ ‭17000 genes (many of which are named) - all genome is known‬ ‭-‬ ‭50% have mammalian homologous‬ ‭-‬ ‭75% of human disease-associated genes have fly homologues‬ ‭-‬ ‭Olfactory memory and behavioral control‬ ‭Many mutant lines →‬ ‭Our best understanding of subsequent events comes from work in fruit flies‬ ‭★‬ ‭1910:‬‭Thomas‬‭Hunt‬‭Morgan‬‭discovered‬‭a‬‭white-eyed‬‭fly‬‭among‬‭a‬‭collection‬‭of‬‭red-eyed‬‭flies.‬‭He‬‭observed‬ ‭the‬‭banding‬‭patterns‬‭of‬‭chromosomes,‬‭and‬‭saw‬‭that‬‭the‬‭same‬‭pattern‬‭was‬‭always‬‭observed‬‭in‬‭white-eyed‬ ‭flies.‬‭With‬‭these‬‭experiments‬‭he‬‭established‬‭the‬‭chromosomal‬‭theory‬‭of‬‭inheritance‬‭for‬‭which‬‭he‬‭won‬‭the‬ ‭Nobel Prize in 1933.‬ ‭★‬ ‭1927:‬ ‭Hermann‬ ‭Muller,‬ ‭discovered‬ ‭X-rays‬ ‭can‬ ‭induce‬ ‭genetic‬ ‭mutations.‬ ‭Muller‬ ‭won‬ ‭the‬ ‭Nobel‬ ‭Prize‬ ‭in‬ ‭1946 for his discovery.‬ ‭15‬ ‭NEURAL DEVELOPMENT – Prof.sse S. Bovetti – A.A 2024-2025 – anno1 semestre1 – Margherita Bosso‬ ‭★‬ ’‭70s‬ ‭and‬ ‭’80s:‬ ‭Ed‬ ‭Lewis,‬ ‭Christiane‬ ‭Nusslein-Volhard,‬ ‭and‬ ‭Eric‬ ‭Wieschaus‬ ‭identified‬‭some‬‭of‬‭the‬‭genes‬ ‭that‬‭establish‬‭the‬‭dorsal-ventral‬‭and‬‭anterior-posterior‬‭axes‬‭of‬‭the‬‭embryo,‬‭as‬‭well‬‭as‬‭the‬‭genes‬‭involved‬‭in‬ ‭segmentation, which specify the body plan. They won the Nobel Prize in 1995.‬ ‭http://nobelprize.org/nobel_prizes/medicine/laureates/1995/index.html‬ ‭http://superstarsofscience.com/scientists‬ ‭★‬ ‭1990’s:‬‭Jules‬‭Hoffmann‬‭used‬‭Drosophila‬‭for‬‭research‬‭on‬‭innate‬‭immunity.‬‭He‬‭discovered‬‭Toll‬‭receptors‬‭and‬ ‭demonstrated‬‭their‬‭importance‬‭for‬‭sensing‬‭and‬‭defending‬‭against‬‭pathogens.‬‭Hoffman‬‭won‬‭the‬‭Nobel‬‭Prize‬ ‭in‬‭2011‬‭for‬‭his‬‭work‬‭on‬‭the‬‭Drosophila‬‭innate‬‭immune‬‭system,‬‭and‬‭shared‬‭the‬‭prize‬‭with‬‭Bruce‬‭Beutler‬‭and‬ ‭Ralph Steinman for their work on innate immunity in mammals.‬ ‭Establishing polarity in the egg‬ ‭ fter‬ ‭fecondation‬ ‭the‬ ‭cell‬‭goes‬‭through‬‭cellular‬‭division‬‭without‬ A ‭formation of the membrane‬‭.‬ ‭In 2 hours: 13 mitotic cycles and 6000 nuclei in a unique cell.‬ ‭Fruit‬ ‭fly‬ ‭embryogenesis‬ ‭differs‬ ‭from‬ ‭that‬ ‭of‬ ‭vertebrates‬‭.‬ ‭In‬ ‭insects,‬ ‭the‬ ‭early‬ ‭embryo‬ ‭does‬ ‭not‬ ‭divide‬ ‭into‬ ‭separate‬ ‭cells;‬ ‭rather,‬ ‭the‬ ‭nucleus‬ ‭alone‬ ‭divides‬ ‭repeatedly‬ ‭until‬ ‭the‬ ‭egg‬ ‭consists‬ ‭of‬ ‭a‬ ‭single‬ ‭cell,‬ ‭which‬ ‭we‬ ‭call‬ ‭a‬‭syncytium‬‭,‬‭with‬‭one‬ ‭continuous cytoplasm containing many nuclei.‬ ‭ imultaneous‬ ‭multi-view‬ ‭imaging‬ ‭of‬ ‭mitotic‬ ‭cycles‬ ‭10-13‬‭in‬‭the‬ S ‭Drosophila‬ ‭syncytial‬ ‭blastoderm‬ ‭(His2Av-GFPS65T‬ ‭transgenic‬ ‭stock).‬ ‭The‬ ‭entire‬ ‭embryo‬‭was‬‭recorded‬‭in‬‭25-second‬‭intervals‬ ‭using‬ ‭light‬ ‭sheet‬ ‭fluorescence‬ ‭microscopy‬ ‭(Tomer‬ ‭et‬ ‭al.,‬ ‭2012),‬ ‭with‬ ‭which‬ ‭we‬ ‭can‬ ‭keep‬ ‭the‬ ‭sample‬ ‭in‬ ‭vivo‬ ‭under‬‭the‬‭microscope‬‭and‬‭marking‬‭cells‬‭with‬‭fluorophores‬ ‭(transgenic‬‭Drosophila‬‭expressing‬‭GFP‬‭under‬‭control‬‭of‬‭a‬ ‭promoter‬ ‭-‬ ‭inducible‬ ‭GFP).‬ ‭Drosophila‬ ‭will‬ ‭be‬ ‭set‬ ‭transparent.‬ ‭Only‬ ‭at‬ ‭that‬ ‭point‬ ‭cells‬ ‭can‬ ‭begin‬ ‭become‬ ‭different‬ ‭from‬ ‭each‬‭other.‬‭All‬‭nuclei‬‭can‬‭detect‬‭what‬‭is‬‭happening‬‭in‬‭the‬ ‭entire‬ ‭structure,‬ ‭while‬ ‭cellularization,‬ ‭the‬ ‭formation‬ ‭of‬ ‭membranes‬ ‭will‬ ‭isolate‬ ‭the‬ ‭cells.‬ ‭So‬ ‭there‬ ‭is‬ ‭a‬ ‭passage‬ ‭from uniform behavior to distinct behavior.‬ ‭https://digital-embryo.janelia.org/‬ ‭ ll‬ ‭the‬ ‭proteins‬ ‭and‬ ‭RNAs‬ ‭are‬ ‭supplied‬ ‭by‬ ‭the‬‭embryo’s‬ A ‭mother:‬ ‭the‬ ‭embryo‬ ‭has‬‭been‬‭doing‬‭something‬‭repetitive‬ ‭using‬ ‭only‬ ‭maternally‬ ‭supplied‬ ‭genes‬ ‭products.‬ ‭Zygotic‬ ‭RNAs‬‭and‬‭proteins‬‭:‬‭these‬‭are‬‭required‬‭to‬‭do‬‭new‬‭things‬‭(present‬‭from‬‭stage13).‬‭Already‬‭5‬‭minutes‬‭later‬‭cells‬‭no‬ ‭longer‬‭have‬‭the‬‭same‬‭shape,‬‭and‬‭a‬‭cephalic‬‭fold‬‭appears‬‭where‬‭the‬‭head‬‭will‬‭form.‬‭The‬‭formation‬‭of‬‭a‬‭cephalic‬‭fold‬ ‭is followed by a process of cell movement and invagination (‬‭no proliferation‬‭).‬ ‭At‬ ‭one‬ ‭point‬ ‭in‬ ‭the‬ ‭anterior‬ ‭part‬ ‭something‬ ‭starts‬ ‭to‬ ‭change‬ ‭in‬ ‭morphology‬ ‭and‬ ‭shape‬ ‭in‬ ‭cells‬‭and‬‭this‬‭induces‬ ‭movements‬‭of‬‭cells‬‭in‬‭the‬‭posterior‬‭part‬‭wi

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