ZOO 3050 Lecture 14: lec 14
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Review: sea urchin gastrulation, emt = mesenchyme, convergent extension, wnt signalling p-cadherin, a-p axis. Using salamander cells because they are nicely pigmented: grey crescent, cytoplasm re-organized/re- oriented, before first division, microtubules gain polarity, grey crescent created by rotation, 1st cleavage divides grey crescent, bilateral symmetry. Epiboly: main difference between frogs and sea urchins, sea urchins have big blastocoel, frogs are much smaller. What are the underlying principles for embryo to form from scratch: need organization, otherwise cells would go everywhere. Spemann"s experiment to show that early blastula cells are totipotent. Such piece can therefore be designated as a. The amphibian gray crescent (gc: equal divisions of gray crescent, two normal tadpoles. If unequal division of gray crescent (one division has it one doesn"t) get belly piece: gray crescent contains precursor cells of primary organizer, temporal specification. Early gastrula induction dependent fate (conditional fate: later gastrula. Create new neural plate induced by transplanted cells, impose their own fate.