Lecture 15 Notes

Lecture 15 Notes - Vandan Desai BIOL 442Developmental...

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Vandan Desai BIOL 442—Developmental Biology 1 Lecture #15—Axis Formation in Vertebrates— Induction and Patterning of the Neural Ectoderm I. Reminder: Events Leading to Specification of D-V Axis (Frogs) :: A. # of tissues are dorsalized after gastrulation = ectoderm, endoderm, and mesoderm B. Organizer —specified on dorsal side of vertebrate embryo (in frogs); induces other cells to take on dorsal cell fate C. Dorso-ventral axis of frog embryo is established by series of inductive interactions involving both paracrine and juxtacrine signals i. These events lead to a pre-gastrula embryo organized as illustrated below: ii. The embryo is pre-gastrula but is already fated to become certain cell types iii. Today’s lecture will focus on events that take place after the organizer is formed and that induce and pattern the neural ectoderm (precursor of CNS) D. D-V patterning events organized in the correct chronological order : i. #1 = Sperm entry marks the future belly/ventral side of embryo & grey crescent forms on future dorsal side ii. #2 = The three dorsalmost vegetal blastomeres ( Nieuwkoop center ) induce the overlying animal cells to make the dorsal lip of the blastopore iii. #3 = Disheveled inhibits GSK3 on the dorsal side allowing β-catenin to go to nucleus of dorsal cells and act as a transcription factor iv. #4 = Goosecoid , a transcription factor activated by Siamois , activates transcription of most organizer genes v. #5 = The organizer dorsalizes the mesoderm and the ectoderm II. How Does the Organizer Induce the Neural Ectoderm? :: A. Organizer induces neural ectoderm on dorsal side; non-neural ectoderm ( skin ) forms on ventral side B. Functions of organizer = i. Gives rise to notochord ii. Orchestrates gastrulation iii. Induces dorsal fates in both the mesoderm and ectoderm (neural ectoderm) Neural ectoderm ( dorsal ) = brain + spinal cord Epidermal ectoderm ( ventral ) => skin Mesoderm ( ventral ) => blood cells, etc. Mesoderm ( dorsal ) => notochord Also, dorsal & ventral endoderm , but not covered
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Vandan Desai BIOL 442—Developmental Biology 2 C. Experimental evidence that the organizer induces the neural ectoderm i. The transplanted organizer ( red cells ) recruit host tissue to form neural tube At ventral side, orchestrate another set of events to develop secondary structures (notochord + neural tube on ventral side) ii. Hans Spemann & Hilde Mangold’s original data on the right : D. Planar versus Vertical Neural Induction— i. The organizer and its axis derivative (the notochord) are both able to induce host tissue to form a neural tube ii. This raises the question of how and when does neural induction occur?
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