lecture 9 Feb3 PDF - BIOL 303 Developmental Biology Early...

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BIOL 303 - Developmental Biology Early Invertebrate Development 1. Patterns of embryonic cleavage 2. Mechanisms of gastrulation 3. Early sea urchin development Axis formation in C. elegans Gilbert, 10ed, p170-173
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Cleavage Early development - cleavage - Rapid and synchronous mitotic divisions, egg cytoplasm divides into blastomeres à Blastula - Biphasic cell cycle, controlled by maternally provided cytoplasmic components - Egg activation leads to (among other things) burst of translation of maternal RNAs - Translation of cyclin B à cyclinB + CDK = “ MPF ” ( Mitosis-Promoting Factor ) - mid-blastula transition ( MBT ): “normal” cell cycle (+G1and G2), asynchronous divisions controlled by the embryo genome “normal” cell cycle Bi-phasic embryonic cell cycle
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Early embryo development – Types of cleavage What determines different cleavage patterns? Early cleavage patterns are distinct and invariable in different species Even with little yolk, there are different types of cleavage Displaced cleavage à different cell sizes Partial cleavage, Telolecithal: cleavage in small portion w/o cytoplasm Yolk is in the middle à cleavage happens around the edge
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Early embryo development – Mechanisms of gastrulation Remember: change of cell shape due to apical constriction driven by actin/myosin, leads to inwards buckling; regulated by Twist and Snail (Droso) Whole tissue layer expands and migrates inwards over internal side of outer layer EMT! Loss of cell-cell interactions (downregulation of E-cadherins (by Snail) and loss of interaction with the basal lamina (integrins)) One sheet drops inwards to form 2 sheets chick Drosophila, Sea urchin frog Sea urchin Frog, sea urchin Outer sheet expands to cover inner layer; mediated by cell division, cell shape changes, intercalation of multiple layers into one
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BIOL 303 - Developmental Biology Early Invertebrate Development 1. Patterns of embryonic cleavage 2. Mechanisms of gastrulation 3. Early sea urchin development Axis formation in C. elegans Gilbert, 10ed, p170-173
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From wikipedia Sea urchin development: overview Swimming blastula
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