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UNC-Chapel Hill BIOL 205 - Lecture 4 - Gastrulation

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GastrulationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Sea urchin gastrulation (a relatively simple example)Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Actin organization dictates the structure of protrusionsIntegrins form an indirect linkage between the ECM and actin networkIntegrins cluster at sites of focal adhesionsSlide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Blastopore Formation (at ~20,000-cell stage)Slide 36Slide 37Slide 38Formation of the Archenteron, Convergent Extension of the Dorsal MesodermSlide 40Epiboly of the Ectoderm – cells divide and move over and around the embryoSlide 42Epiboly of the EctodermElimination of the blastocoel, mesenchyme migrationSlide 45Slide 46Slide 47Slide 48Slide 49Slide 50Slide 51Slide 52Slide 53Slide 54Slide 55Slide 56Slide 57Slide 58GastrulationWhich cells move during gastrulation, and where do they go?How are these cell movements accomplished?From what parts of the embryo do different tissues arise?CLEAVAGE PATTERNSII. MEROBLASTIC (INCOMPLETE CLEAVAGE) A. Telolecithal (Dense yolk throughout most of cell)animalvegetalEarly cleavage in Xenopus(from Gilbert, Developmental Biology)The Mid-Blastula Transition Growth phases added to Cell Cycle (12 rounds of division)Embryo starts transcribing its own RNAXenopus (frog) gastrulationBlastulaEndodermMesodermEctodermThree germ layersSea urchin gastrulation (a relatively simple example)Sea urchin cleavageSea urchin gastrulation(from Gilbert, Developmental Biology)Sea urchin gastrulationPrimary mesenchyme cellsChanges in adhesion drive primary mesenchyme invagination(cadherins are endocytosed)Adherens junctionsEpithelium (sheet of cells)Changes in adhesion drive primary mesenchyme invagination(cadherins are endocytosed)(from Gilbert, Developmental Biology)Sea urchin mesenchyme cells migrate, fuse and form spicules(syncytium = cells sharing cytoplasm)Actin organization dictates the structure of protrusionsIntegrins form an indirect linkage between the ECM and actin network(inside)(outside)Focal adhesionsIntegrins cluster at sites of focal adhesionsSea urchin gastrulation(from Gilbert, Developmental Biology)Sea urchin gastrulationArchenteron formation(from Gilbert, Developmental Biology)(from Gilbert, Developmental Biology)Vegetal plate invaginationAdherens junctionsApical constriction of the actin cytoskeleton could also cause the sheet to bend(from Gilbert, Developmental Biology)Sea urchin gastrulationGrowth of the archenteron(from Gilbert, Developmental Biology)Convergenceand extensionin three dimensions(from Gilbert, Developmental Biology)Sea urchin gastrulation and fate mapEctodermMesodermEndodermFate mapping method (early stage mouse embryo)(From Deb et al., Science 311: 992-996 (2006) – subsequently retracted)3-cell stage 4-cell stage 8-cell stage blastocystTypes of Movement in GastrulationLocal inward bucklingof an epithelium Inward movement of a cell layer around a point or edge Movement of individual cells or small groups from an epithelium into a cavity Spread of an outside cell layer (as a unit) to envelop a yolk mass or deeper layerSplitting layers of cells (sometimes used to describe coordinated ingression) MIGRATION Movement of individual cells over other cells or matrix(from Gilbert, Developmental Biology)Gastrulation in frogsXenopus gastrulationA Fate Map of the Xenopus BlastulaMost Exterior Cellsform ectoderm or endoderm Most Interior Cellsform mesodermSea urchinMesodermBlastopore Formation (at ~20,000-cell stage)spermentry(~20,000 cells at this stage)Apical constriction of bottle cells drivesblastopore invaginationArchenteronMesodermINVOLUTIONaround dorsal lipMarginal Zone CellsInvolution of marginal zone cellsFormation of the Archenteron, Convergent Extension of the Dorsal MesodermConvergence and extension in three dimensionsFigure 10.7Epiboly of the Ectoderm – cells divide and move over and around the embryoEpiboly of the EctodermElimination of the blastocoel, mesenchyme migrationGastrulation finishedEndodermMesodermEctodermEctoderm (outer layer) skin, central nervous system (brain, spinal cord), peripheral nervous system (and other structures, including some bone, cartilage, and connective tissue in the head)EctodermMESODERM (middle layer) muscles, connective tissue, notochord, bones & cartilage, circulatory system (blood and blood vessels), urogenital system (kidneys, gonads)MesodermENDODERM (inner layer) Gut (entire digestive system), liver, lungs, pancreas, salivary glandsEndodermNeurulation separates the ectoderm intoneural and epidermal cell fatesAdherens junctionsFigure 21.25 Essential Cell BiologyNeurulation is driven by cytoskeletal and cell-shape changes similar to those that drive gastrulationNeural tube formationDorsal-Most CellsFigure 12.3Neurulation: finishing the jobDefects in neural tube closure are among the most common birth defectsNumbers indicate regions of neural tube closure.Figure 12.5Spina bifidaspinal cord• failure of posterior neural tube to close• can cause paralysis and loss of bowel/bladder control• 1 in 1000 newborns affectedIt is estimated that 50% of human neural tube defects would be prevented if all women of childbearing age take supplemental folic acid(vitamin B12)400 g/dayDifferential adhesion helps the neural tube and epidermis to separate from each otherHatta and Takeichi (1986) NatureE-cadherinN-cadherinepidermisNeural crest cellsmigrate from the CNS to form the peripheral nervous


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UNC-Chapel Hill BIOL 205 - Lecture 4 - Gastrulation

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