it is not birth, marriage or death, but gastrulation which is truly … powerpoints... ·...
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..It is not birth, marriage or death, but gastrulation which is
truly the most important time in your life..
Lewis Wolpert, 1986
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Initial asymmetry in the amphibian egg
epidermisnervous system
Ectoderm
gutEndoderm
Mesodermblood, bone, heart, organs
1-2 mm in diameter
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Cleavage in the frog egg
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Inside the blastula
sea urchin blastula
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Steps in early embryonic development
Multiple mitotic divisions
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Gastrulation
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Fate map of the Xenopus gastrula
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Hans SpemannNobel Prize in 1935
Hilde Mangold
Spemann’s organizerHensen’s nodeEmbryonic shield
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A-P patterning during neural induction
Retinoic acidFGFs
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Experiments:
1) Dissociated cells
2) Dominant negative activin receptor
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The BMP signaling cascade
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Inhibitors of BMP signaling
Noggin-BMP4 Follistatin-Activin A
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Different BMP antagonists
BMP-4 BMP-7 Activin
Noggin
Chordin
Follistatin
++
++
+
+
+
++ +++
-
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Cloning of NogginSmith and Harland 1992
Chordin expression
Cerberus, Gremlin, Dan, Drm,Ogon/sizzled
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The test: Injection of chordin induces a second axis
Depletion
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Model for neural induction in amphibians
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Things are not as simple as they seem....
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Drosophila embryo
ventral neuroectoderm
Mechanisms are conserved (although inverted) in Drosophila
Chordin
BMP
Anti-neural(ventralizing)
Sog
DPP
Anti-neural(dorsalizing)
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Coming up:
Tue 1/24 Class Discussion of paper(Wilson & Hemmati-Brivanlou, 1995)Lecture (Patterning)
Fri 1/27 Lecture (Patterning cont’d)Class Discussion of paper(Hynes et al., 2000)
Tue 1/31 QUIZ Presentation (patterning)Lecture (Neurogenesis)