BIOL413 Developmental Biology Lecture 3 PDF

Chapter 3 notes are in the Moodle. FOR NEXT WEEK: Read Heasman et. al (1994) carefully. Expect a short test and/or in-class questions.  BIOL 413 – Developmental Biology Cell to Cell Communication in Development 10th Edition, Chapter 3 Cel...

Chapter 3 notes are in the Moodle. FOR NEXT WEEK: Read Heasman et. al (1994) carefully. Expect a short test and/or in-class questions.  BIOL 413 – Developmental Biology Cell to Cell Communication in Development 10th Edition, Chapter 3 Cell-Cell Communication in Development 11th Edition, Cell-Cell Communication Mechanisms of Morphogenesis Morphogenesis Question Maimonides (RaMBaM) 1135-1204 Monument in Cordoba, Spain https://commons.wikimedia.org/ Morphogenesis Question  How can matter alone construct itself into the organized tissues of the embryo? How are separate tissues formed from population of cells? How are organs made of tissues? How do organs form in particular locations? How do migrating cells reach their destinations? How do organs and their component cells grow? How is their growth coordinated throughout development? How can some organs, such as the skin and the intestine, constantly regenerate themselves through stem cell division? How do organs achieve polarity?  Remember! – The cells of an embryo can be epithelial or mescenchymal. REMINDER Morphogenesis – a limited range of variations in processes of a cell within epithelial and mesenchymal cells. Types of morphogenic variations include: Direction and number of cell divisions versus  Epithelial cells: Attach to one another and can form sheets and tubes.  Mescenchymal cells: Migrate individually. Form extensive extracellular matrices which keep the individual cells seperate.  Cells create structured organs via a few processes. All of these processes involve the cell surface. 3 behaviours requiring cell-cell communication via the cell surface: – Cell adhesion – Cell migration – Cell signaling Cell Adhesion Morphogenesis focuses on the cell membrane and its interactions with the peripheral cytoplasm. Cell Adhesion Initial thought the membrane is the same in all cells. Observations of fertilization and early embryonic development suggests otherwise. Re-aggregation of cells from amphibian neurulae A study that illustrates that even in this early stage, the presumptive cells have already differentiated in ways that allows them to segregate following experimental disaggregation. Townes and Holtfreter 1955 Re-aggregation of cells from amphibian neurulae A study that illustrates that even in this early stage, the presumptive cells have already differentiated in ways that allows them to segregate following experimental disaggregation. Townes and Holtfreter 1955 Sorting out and reconstruction of spatial relationships in aggregates of embryonic amphibian cells Classic study by Townes and Holtfreter (1955): A variety of different disaggregated cells lines will display enough differentiation to segregate into separate structural cell groupings. Cell Adhesion Selective affinity Inner surface of the ectoderm (+) affinity for the mesodermal cells Inner surface of the ectoderm(-) affinity for the endoderm Cell Adhesion Selective affinity Mesoderm  (+) affinities for both ectodermal and endodermal cells. Selective affinity Axial mesoderm- gives rise to notochord. Selective affinity  In summary: Somehow the cells are able to sort out into their proper embryonic positions. Selective affinities change during development.  Why the change? Because the embryonic cells do not have a single stable relationship with other cell types.  Tissues from later-stage mammalian and chick embryos were made into single cell suspensions. – How? – What was the end result? Thermodynamic model of cell interactions Cells do not sort randomly. They actively move to create tissue organizations. What forces direct cell movement during morphogenesis? Thermodynamic model of cell interactions Differential adhesion hypothesis: Tries to explain patterns of cell sorting based on thermodynamic principles. Thermodynamic model of cell interactions 1964- Steinberg’s Experiment Certain cell types move centrally when combined with some cell types BUT migrate peripherally when combined with others. Malcolm Steinberg 5 hours after mixing 19 hours after mixing 2 days after mixing  Simple schematic demonstrating a logic statement for the properties of differential cell adhesion  In physics, the dyne is a unit of force. One dyne is equal to 10 µN (micronewtons). Equivalently, the dyne is defined as "the force required to accelerate a mass of one gram at a rate of one centimetre per second squared. In developmental biology, “dynes per centimeter” are units traditionally used to measure surface tension. For example, the surface tension of distilled water is 72 dyn/cm at 25 °C. Water displays cohesion (surface tension), but this cohesion varies based upon other physical factors such as solute concentrations and temperature. Hierarchy of cell sorting in order of decreasing surface tensions In this segregation series, cells that aggregate more towards the interior have a greater surface tension score (dyne/cm) than do the cells in the outer later. These differences in surface tension suggest one mechanism by which differentiation may proceed. Hierarchy of cell sorting in order of decreasing surface tensions Cells interact to form an aggregate with the smallest interfacial energy. Cell Rearrangement: Most thermodynamically stable pattern preferred. Cadherins and cell adhesion Recent evidence: Boundaries between tissues can be created by different cell types having i. different types and ii. different amounts of cell adhesion molecules. Cadherins and cell adhesion Recent evidence: Several classes of molecules can mediate cell adhesion… But, the major cell adhesion molecules cadherins. Cadherins and cell adhesion Cadherins: are calcium-dependent adhesion molecules. Transmembrane proteins that interact with other cadherins on adjacent cells. Anchored inside the cell by a complex of proteins called catenins Cadherin-mediated cell adhesion Cadherin-mediated cell adhesion Questions 1. What does the cadherin& catenin binding to the actin (microfilament) cytoskeleton of the cell provide? 2. What do you expect to see if cadhenin function is interfered with?  Maternal cadherin mRNA is attacked Cadherin proteins perform several related functions Their external domains help to adhere cells together. They link to and help assemble the actin cytoskeleton. They can serve as signaling molecules changing a cell's gene expression.  In vertebrate embryos, several major cadherin types have been identified. E-cadherin: is expressed on all early mammalian embryonic cells (even at the zygote stage). - What about later in development & E-cadherin ?  P-cadherin: mainly found in placenta, where it helps the placenta to stick to uterus. N-cadherin: highly expressed on cells of the developing CNS. R-cadherin: important in retina formation.  A group of cadherins called protocadherins do not attach to actin skeleton through catenins. Expressing similar protocadherins is important for keeping migrating epithelial cells together. What about expressing dissimilar protocadherins?  Steinberg and Takeichi (1994) -Show that cells sort themselves based on cadherin amount.  Cadherin-dependent sorting directly correlates with surface tension. The cell sorting hierarchy is strictly dependent on the cadherin interactions between the cells. Importance of the amount of cadherin for correct morphogenesis  The type of cadherin expressed is also important in development. R-cadherin and B-cadherin do not bind well to each other. N-cadherin is important in separating the neural precursors.  What happens if epidermal cells are made to express N-cadherin? Or if N-cadherin is blocked in prospective neural cells? The border between the skin and the nervous system fails to form properly. Importance of the types of cadherin for correct morphogenesis The neural tube Not in mutant separates cleanly from embryos where N- surface epidermis cadherin fails to be made Importance of the types of cadherin for correct morphogenesis (Part 2) Cell Migration Common for both mesenchymal and epithelial cells. A lot of movement during gastrulation to form the 3 germ layers. The first stage of migration is POLARIZATION. Cell Migration POLARIZATION is where a cell defines its front and its back. It can be directed by: - diffusing signals or - signals from the extracellular matrix. These signals reorganize the cytoskeleton. Cell Migration Cell Migration Integrins: - span the cell membrane. - connect extracullular matrix to actin cytoskeleton. This connection of actin to integrin forms focal adhesion on the cell membrane, where the membrane contacts the extracellular matrix. Cell Signaling Adhesion Migration Differentiation Division – All regulated by signals from one cell being received by another cell. Example: Development of the vertebrate eye. Eye development In the vertebrate eye The development of the eye occurs by one group of cells changing the behaviour of an adjacent set of cells. Causing them to : change their shape, mitotic rate or cell fate. Eye development This type of interaction at close range is called INDUCTION. INDUCTION AS1 -Inducer: the tissue that produces signal(s) which changes the behaviour of the other tissue. -Paracrine factors: proteins made by a cell or a group of cells that alter the behaviour or differentiation of adjacent cells. - Secreted into the extracellular matrix and affect the close neigbours. Slide 63 AS1 endorcine factors ile ilgili bir iki satir yaz A.S, 30-Nov-18 INDUCTION -Responder: the cell or tissue being induced. -Responding tissue must have both a receptor protein for the inducing factor and the ABILITY to respond to the signal. - This ability to respond to the signal is called COMPETENCE Competence Competence is the ability to respond to an inductive signal. May depend on the presence of: - a particular receptor - a transducing mechanism - a particular transcription factor A cell’s competence for a particular response can change over time. Only head ectoderm is competent to respond to the signals from the optic vesicle by producing a lens. Reciprocal Induction Using the eye development example: Once the lens has formed, it induces other tissues, including the optic vesicle itself. The inducer (in this case the optic vesicle) becomes the induced. Schematic diagram of induction of the mouse lens (Part 1) Schematic diagram of induction of the mouse lens (Part 2) Major Modes of Inductive Interactions Major Modes of Inductive Interactions Instructive interaction A signal from the inducing cell is necessary for initiating new gene expression in the responding cell. Without the inducing cell, the responding cell is not capable of responding in that particular way. Major Modes of Inductive Interactions Instructive interaction Ex. Mesoderm induces ectoderm to form region- specific structures: thigh mesoderm + wing ectoderm = thigh feather. Major Modes of Inductive Interactions Permissive interaction The responding cell contains all the potentials that are to be expressed, and needs only an environment that allows expression of these traits. Genetic Specificity of Interaction Example from frog and newt development Newt larva part-way through metamorphosis, wikipedia.org Frog larva animals.about.com Genetic Specificity of Interaction Example from frog and newt development Frog Newt wikipedia.org wikipedia.org Genetic Specificity of Interaction Major Modes of Inductive Interactions Permissive interaction Example from frog and newt development Example: Species-specific differences in mouth parts: mesoderm induces ectoderm to form mouth, but ectoderm responds by making the kind of mouth it “knows” how to make. Major Modes of Inductive Interactions Permissive interaction Example from frog and newt development The instructions sent by the mesenchymal tissue can cross species barrier. The response of the epithelium is species-specific. PARACRINE FACTORS Some inductive event could occur despite a filter separating the epithelial and mesenchymal cells. Others were blocked. PARACRINE FACTORS Some of the inducers are soluble molecules and can pass through the small pores. Other inductive events need physical contact. PARACRINE FACTORS Juxtacrine Interactions: Membrane proteins on one cell surface interact with receptor proteins on adjacent cell surfaces. http://www.nature.com/jcbfm/journal/v20/n10/fig_tab/9590992f1.html PARACRINE FACTORS Paracrine Interactions: Proteins synthesized by one cell can diffuse over small distances to induce changes in neigbouring cells. http://www.nature.com/jcbfm/journal/v20/n10/fig_tab/9590992f1.html PARACRINE FACTORS Autocrine interaction is a specific type of paracrine interactions: Here, the same cells that secrete paracrine factors also respond to them. http://www.nature.com/jcbfm/journal/v20/n10/fig_tab/9590992f1.html  PARACRINE FACTORS ‘The factors active in creating the Drosophila eye or heart are very similar to those used in generating mammalian organs’. FOUR MAJOR FAMILIES: - Fibroblast growth factor (FGF) family - Hedgehog Family - Wnt Family - TGF-β  Fibroblast Growth Factors and RTK Pathway Paracrine factors. Nearly 2 dozen structurally related members. FGF genes can generate 100s of protein isoforms. FGF1 (acidic FGF) Important during regeneration. FGF2 (basic FGF)  Important in blood vessel formation. FGF7 (keratinocyte growth factor)  Important in skin development FGF8  Important in limb development and lens induction. Fgf8 in the developing chick. Fibroblast Growth Factors FGFs often work by activating a set of receptor tyrosine kinases called FIBROBLAST GROWTH FACTOR RECEPTORS (FGFRs).  RTK Pathway: One of the first signal transduction pathways to unite various areas of development. RTK signal transduction pathway RTK signal transduction pathway JAK-STAT Pathway JAK-STAT Pathway Cytoplasmic domain of the receptor- Linked to Janus Kinase (JAK) STAT- (signal transducers and activators of transcription) Hedgehog signal transduction pathway Often used by embryos to create boundaries between tissues. Cholesterol is critical in letting the Hedgehog protein to anchor to its receptor cell’s cell membrane. This is important in binding the paracrine factor to its receptor. Hedgehog signal transduction pathway Vertebrates have at least 3 homologues of the Drosophila hedgehog gene: - Sonic hedgehog (shh) - desert hedgehog (dhh) - indian hedgehog (ihh) Sonic the Hedgehog (Video game character) Hedgehog signal transduction pathway - Sonic hedgehog (shh) ‘Sonic Hedgehog’ Sounded Funny, at First “…A gene with a funny name may be linked to a medical condition that can be heartbreaking. The human variant of the fruit fly’s “hedgehog” gene, known as “sonic hedgehog” after the video-game character, has been linked to a condition known as Holoprosencephaly, which can result in severe brain, skull and facial defects.” www.nytimes.com/2006/11/12/weekinreview/12schwartz.html Sonic the Hedgehog (Video game character) (A) Sonic hedgehog expression is shown by in situ hybridization in the nervous system, gut, and limb bud of a chick embryo. (B) Head of a cyclopic lamb From: Expression of the Sonic hedgehog (SHH) Gene during Early Human Development and Phenotypic Expression of New Mutations Causing Holoprosencephaly Hum Mol Genet. 1999;8(9):1683-1689. doi:10.1093/hmg/8.9.1683 Hum Mol Genet | © 1999 Oxford University Press Hedgehog signal transduction pathway Desert hedgehog protein is found in Sertoli cells of the testes. Mice homozygous for a null allel of Dhh (Dhh -/-) have defective spermatogenesis. Hedgehog signal transduction pathway Indian hedgehod: – expressed in the gut and cartilage – Important in postnatal bone growth Sonic hedgehog has the greatest number of functions – involved in correct development of motor neurons Hedgehog signal transduction pathway Hedgehog signal transduction pathway Hedgehog signal transduction pathway Proteins of the Hedgehog family function by binding to a receptor called Patched. Patched protein is not a signal transducer. It is bound to a signal transducer, the Smoothened protein. Patched protein prevents Smoothened from functioning. Hedgehog signal transduction pathway Hedgehog signal transduction pathway