Embryonic Development 2/2 PDF

Embryonic Development 2/2 Early stage of implantation compaction Implantation starts at day 5 to 6 Tuchmann-Duplessis et al. 1972 and is complete by day 12 approx. Stem cells Stem cells are capable of unlimited self renewal and able to differentiate into more specialized cell types: 1. Totipotent st...

Embryonic Development 2/2 Early stage of implantation compaction Implantation starts at day 5 to 6 Tuchmann-Duplessis et al. 1972 and is complete by day 12 approx. Stem cells Stem cells are capable of unlimited self renewal and able to differentiate into more specialized cell types: 1. Totipotent stem cells: Embryonic cells from the morula: can give rise to every cell type of the body and form an entire organism. 2. Pluripotent stem cells Embryonic stem cells from the inner cell mass of the blastocyst can generate virtually all cell types (excluding the placenta). 3. Multipotent stem cells (Adult stem cells or progenitor cells): found at specific sites (niches). Can only give rise to a limited number of cell types. For example, a hematopoietic cell can differentiate into one of the blood cell types. Embryonic Stem Cells Blastocysts 88 hours post coitum (hpc) Embryonic stem cells derived from the inner cell mass (ICM) of blastocysts will contribute to all tissues of a chimaeric animal if injected into a blastocyst (however, when injected into tissue other than a blastocyst, will result in a tumour) M. J. Evans & S. M. Hunter Delayed Blastocysts 180hpc - Knocking out an unwanted gene - Knocking in a wanted gene - Introducing desired modifications of specific genes → understanding of functions of various genes/proteins → gene therapy → stem cell therapy http://nobelprize.org/nobel_prizes/medicine/laureates/2007/ev ans-lecture.html Retinal Stem Cell Transplant Retinal stem cells (genetically modified to express green-fluorescent protein) from the ciliary margin of adult human donors were transplanted into the mouse retina Some transplanted cells differentiated into photoreceptors, some other into RPE cells Coles BL et al (2004) Proc Natl Acad Sci USA 101, 15772 Rod precursor cell transplant: MacLaren RE et al Nature 444, 203 – 207 (2006). 2015 Feb 7;385(9967):509-16 2015 Feb 7;385(9967):509-16. Embryonic stem cell transplant trials for macular degenerations: atrophic form of AMD and Stargardt’s disease Before transplant 1 week after transplant 6 weeks after transplant Before transplant 3 months after transplant ClinicalTrials.gov, NCT01345006 (Stargardt's macular dystrophy) and NCT01344993 (age-related macular degeneration); Lancet 2015 Feb 7;385(9967):509-16. https://pubmed.ncbi.nlm.nih.gov/25458728/ Induced pluripotent stem cells (ipSCs) The Nobel Prize in Physiology or Medicine 2012 for the discovery that mature cells can be reprogrammed to become pluripotent: Sir John B. Gurdon, Shinya Yamanaka http://www.nobelprize.org/nobel_prizes/medicine/laureates/2012/gurdon-lecture.html http://www.nobelprize.org/nobel_prizes/medicine/laureates/2012/yamanaka-lecture.html iPSCs for treatment of retinal degenerative diseases Masayo Takahashi group had reprogrammed some fibroblasts from the patient's skin to produce iPS cells. Then those iPS cells were treated with a combination of chemicals to differentiate into RPE cells and grow into a sheet for implantation. An AMD patient in her 70s received transplant of RPE cells derived from her skin Sheet of RPE cells derived from skin fibroblasts of the transplant recipient So far no potential side effects such as an immune reaction or inducing cancerous growth. Jennifer Doudna: Genome Editing with CRISPR-Cas Systems: https://www.youtube.com/watch? v=Vxs_34rfO8E&feature=youtu.be https://innovativegenomics.org/education/digital-resources/what-is-crispr/ https://www.bbc.co.uk/iplayer/episode/m000dt7d/storyville-the-gene-revolution-changing-human-nature https://www.biointeractive.org/classroom-resources/crispr-cas-9-mechanism-applications Embryonic Development   Implantation (5-12 days) Weeks 2-4 of the human embryonic development: -  gastrulation neurulation Early embryonic origin of different organs Week Two Completion of implantation - Formation of bilaminar germ disc - Implantation of the blastocyst Formation of the bilaminar germ disc Day 9 Inner cell mass divides to form: Epiblast: divides to line amniotic cavity & forms all the tissues of the embryo. Hypoblast: lines blastocoel & gives rise to the yolk sac. Scott F. Gilbert: Developmental Biology Week Three Gastrulation - Neurulation - Timing of key developmental events: ~15 days ~18 days Gastrulation begins ~20-21 days ~23 days Gastrulation complete Neurulation begins Neurulation complete Heart development begins Gastrulation  Gastrulation is one of the key stages in the development of multicellular animals.  Several important events occur during gastrulation:  Three primary germ layers are established  The primary body axis is established  Cells move into new positions, paving the way for the inductive interactions necessary for neurulation and organogenesis Appearance of the primitive streak: Carnegie stage 6 (day 15) The first sign of gastrulation is the formation of the primitive streak - Epiblast cells ingress, forming a furrow at the tail end of the embryonic disc The primitive streak establishes the longitudinal axis of bilateral symmetry in the embryo Prof. Kohei Shiota, Kyoto collection Gastrulation Epiblast cells move through the primitive streak and (Hensen's) node 14-15 days, ingressing epiblast cells replace the hypoblast cells 16 days, the ingressing cells fan out to form the mesodermal layer Scott F. Gilbert: Developmental Biology Gastrulation  Scott F. Gilbert: Developmental Biology Epiblast cells migrate through the primitive streak to form 3 cell lineages (germ layers):  Ectoderm - outer layer (Greek: Ektos, outside)  Mesoderm – Middle layer (Greek: Mesos, middle)  Endoderm - Internal layer (Greek: Endon, within) Three Germ Layers: ©Office of Science Policy, the National Institutes of Health Summary of gastrulation: The process of gastrulation: − forms a gastrula from a blastula − converts a 2 layered embryo into a 3 layered embryo − forms the 3 primary germ layers: Ectoderm  for example CNS, epidermis, melanocytes  Endoderm  for example lung, thyroid, and pancreatic cells  Mesoderm  for example heart, muscle, and kidney cells  Timing of key developmental events: ~15 days ~18 days Gastrulation begins ~20-21 days ~23 days Gastrulation complete Neurulation begins Neurulation complete Heart development begins http://www.youtube.com/watch?v=UgT5rUQ9EmQ Neurulation begins with the formation of the notochord Neurulation begins with the formation of the notochord  The notochord is a flexible rod, derived from mesoderm, found in embryos of all chordates.  The notochord induces the formation of the central nervous system (CNS) by signalling to the ectoderm layer above it to form the neural plate.  In higher vertebrates the notochord regresses during development. Neurulation  Neurulation is the first step in organogenesis in the developing embryo  Neurulation gets underway while gastrulation is still occurring  Neurulation refers to the folding process resulting in formation of neural tube. The embryo at this stage is termed the neurula.  The neural tube will differentiate into the spinal cord and brain (central nervous system = CNS)  Neurulation begins the formation of the CNS Neurulation 1: Formation of the notochord: Day 16 Head Future site of mouth Notochord Node Primitive Streak http://www.visembryo.com Tail Neurulation: Formation of the neural plate and then neural tube The mesodermally-derived notochord induces the overlying ectoderm to form the neural plate. The most lateral portions of the neural plate will give rise to the neural crest. The lateral parts of neural plate rise up and the centre invaginates to form the neural groove The neural tube fuses and separates from the overlying ectoderm. Neural crest cells separate from the neural tube and migrate into the periphery. Basic Neurochemistry Ed. Siegal et al. (Modified from Cowan et al.) Neurulation: Formation of the neural tube At trunk level in the embryo, the neural tube forms the spinal cord surrounding a central canal. Basic Neurochemistry Ed. Siegal et al. (Modified from Cowan et al.) Summary: Primary neurulation S.F. Gilbert (Photographs courtesy of K. Tosney and G. Schoenwolf; drawings after Smith and Schoenwolf 1997) MHP – medial hinge point; DLHP – dorsolateral hinge point Video-clip of neurulation in action: https://www.youtube.com/watch?v=lGLexQR9xGs Chick Embryo Mid-brain Fore-brain Hind-brain Heart Somites Notochord Neural groove Hensen’s node Remains of primitive streak Gray’s anatomy (from Duval’s “Atlas d’Embryologie.”) In summary the process of neurulation:  is the first step of organogenesis in vertebrate embryos  starts with the formation of the notochord, followed by the neural plate then neural tube  finishes at day 23-24 with closure of the neuropores  leads to the formation of the future brain and spinal cord (central nervous system)  leads to the formation of the neural crest Summary: Primary neurulation S.F. Gilbert (Photographs courtesy of K. Tosney and G. Schoenwolf; drawings after Smith and Schoenwolf 1997) Importance of the neural crest:  neural crest cells originate from ectoderm at the top of the neural tube, then migrate extensively  the fate of a migrating neural crest cell is largely determined by its final destination Scott F. Gilbert: Developmental Biology Summary: Milestones in embryonic development:  Week 3:       Gastrulation starts Notochord appears Neurulation starts Rudimentary vasculature starts to form Gastrulation completes Week 4:   Neurulation ends with closure of neural tube: CNS starts to develop  Heart starts to beat  Liver & spleen start to form Week 5:   Hands and legs start to form  Rudimentary blood starts to circulate Week 6:   Week 7:   Lungs start to form Spontaneous movements begin Week 8:  All essential organs have at least begun to form Learning outcomes from Embryonic Development lectures (part 3): Define and describe different types of stem cells and how they can be used for treatment of blinding diseases. Define and describe the process of gastrulation. What are the three germ layers formed? Define and describe the process of neurulation and its importance in formation of the CNS (and eye).