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7-Amphibian Gastrulation.pdf

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Western University
Biology 3338A
Sashko Damjanovski

Form germ layers and axis – ant, post, dorsal and ventral, left and right. •  Dividing maternal determiniants; different pigments in the egg •  Where the sperm fertilizes is anterior – opposite is posterior; symmetry is broken •  Animal will be dorsal; vegetal will be ventral •  Sperm receptor is on animal side ; can only fertilize on that one area •  First cleavage bisects the sperm entry point; left and right. •  There is no G phase in the early stages •  Many cell divisions and still has a marginal zone Recap: •  ß-catenin at the bottom of the egg with micromeres •  Determines posterior •  Vertebrate – need a dorsal area – sperm entry point = anterior, opposite is the posterior; Looking at the side of an embryo; there is no blastocoel cavity yet but there is something called a marginal/equitorial region. The top is animal, bottom is vegetal – sperm will only fertilize one half. Sperm fertilization occurs on the anterior side; opposite will be posterior. Dorsal forms across the animal half and ventral is on vegetal half. Gastrulation will start at the marginal zone – stage 8 is before gastrulation, stage 9 is when gastrulation starts. Transcription starts and dorsal and germ layers will form. Ectoderm = animal Endoderm = vegetal 2 Animal cap – above the blastocoel cavity; if cultured alone, it will remain ectoderm. Add endoderm to ectoderm, endoderm will induce animal cap and form mesoderm Organizer: organizes dorsal and form dorsal structure (vertebrate column) Different parts of the embryo have different functions Different types of mesoderm formed by concentrations of morphogens – activin Dorsal has special events 3 Animal cap cells will be ectoderm; vegetal cells will be endoderm Dorsal lip = opposite the sperm entry point; posterior - Involution starts here – cell goes to anterior – becomes the dorsal axis (makes spine and vertebrae etc) If you mes up maternal factors you will disrupt gastrulation VegT = endoderm; if you don’t have this you wont have endoderm Marginal zone -  Some is endo- or ectoderm -  The cell that starts involuding will go all the way to the anterior via gastrulation -  Next cells will involute and start lining the blastocoel -  Will also make mesoderm -  Dorsal mesoderm = spine (opposite sperm entry point) 4 Dorsal lip spreads and will go to the lateral lip and a ventral lip – cells involuting from all parts – makes a ring Epiboly is also occuring Blastopore lip closes and becomes the posterior anus (gastrulation finishes) 5 Bottle cells – at the dorsal lip – start the process (ßcatenin signaling); bottle cells are already commited with maternal determinants. If you put on endoderm it will start gastrulation. Will constrict the apex – contractile ring (actin and myosin) Bottle cells sink into the endoderm and start other cell movements .As cells follow the bottle cells, thereis a rearrangement of cells. Pharyngeal – form part of the pharynx by rearrangement – in contact with the blastocoel cavity Interaction with ectoderm by endoderm (induction of mesoderm) Cells going into the blastopore lip are forming the archenteron – lined by ectoderm As endoderm is migrating you will form mesoderm Endodermal cells migrating in and inducing mesodmerm Endoderm involutes and ectoderm does not IMZ (involuting marginal zone – equitorial region; endoderm) NIMZ (non-involuting marginal zone) End up with only ectoderm on the external – all endoderm has formed on the inside. Epiboly is driving the ectoderm down 7 Bottle cells sink. Rearrangement of the endoderm. IMZ endoderm cause rearragement Cells have to have integrin and fibronectin to move along each other Endoderm moving along ectoderm induced mesoderm 8 Archenteron = gut AS
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