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BRAIN VERSUS SKIN DEVELOPMENT IN FLIES
LECTURE 7: BRAIN VERSUS SKIN DEVELOPMENT IN FLIES
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Ventral Epidermal Genes Neural Genes
High Low None [Dorsal] Epidermal Genes Dpp Neuronal Genes Brk, Sog Dorsal Genes AS-C Rho Ventral Epidermal Genes Neural Genes Snail Neural Genes Twist Mesodermal Genes = M e s o d r m N n - u a l E c t
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Dorsal Meso Neuro Epi dpp sog dpp “sog” snail
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dpp versus sog Expression
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Dpp versus Sog Function
Nucleus Epidermal genes (e.g. dpp) Neural genes (e.g. AS-C) Dpp Receptor Dorsal or Lateral Region Cell Inside Outside Outside Inside Dpp Protein Signal Relay Off On Off On No Dorsal Repressor From Mother dpp mRNA Off On D N A Regulatory Region Coding Region Nucleus Dorsal Region Cell
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dpp- versus sog- Mutants
Mesodermal Genes Neuronal Genes Neuronal Genes Epidermal Genes X Dpp Sog = M e s o d r m N n - u a l E c t
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dpp- Mutant Sog Neuronal Genes Mesodermal Genes = M e s o d r m N n -
c t
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dpp- Mutant
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sog- Mutant X Epidermal Genes Dpp Neuronal Genes Sog Neuronal Genes
Mesodermal Genes Neuronal Genes Epidermal Genes Neuronal Genes Dpp X Sog = M e s o d r m N n - u a l E c t
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sog- Mutant Epidermal Genes Dpp Neuronal Genes Mesodermal Genes = M e
c t
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sog- Mutant
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The Default State of Ectoderm is Neural
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Sog diffuses and patterns the dorsal region
The Players Dpp: A signal that promotes epidermal fates Sog: A secreted inhibitor of Dpp Tolloid = Tld: A protease produced in dorsal cells that cleaves and destroys Sog
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Sog diffuses and patterns the dorsal region
Embryonic Covering Epidermis Low Dpp Hi Dpp Dpp Tld Sog
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Subdivision of the Neuroectoderm
High Low None [Dorsal] Dpp Non-neural genes Neural genes Neuronal genes Msh Ind Vnd = M e s o d e r m = N e u r o e c t o d e r m = N o n - N e u r a l E c t o d e r m
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Patterning the Neuroectoderm in Flies and Mice
Dorsal Dpp ind msh vnd dpp Drosophila Neuroectoderm Mouse Neural Tube Sonic Hh BMPs Msx Nkx2.2 Gsh
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Ventral Dominant Repression
msh ind vnd V
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Dpp Dl Dl Dpp signaling represses ind more effectively than msh msh
X row 3 ind msh Dl row 2 vnd Dl ind, msh row 1
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Dpp Dl Dl Neuroectodermal patterning in a vnd- mutant msh ind X row 3
ind, msh row 1 X
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Dpp Dl Dl Neuroectodermal patterning in a vnd- mutant msh ind X row 3
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Dpp Dl Dl Neuroectodermal patterning in an ind- mutant msh ind X row 3
vnd Dl ind, msh row 1
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Dpp Dl Dl Neuroectodermal patterning in an ind- mutant msh row 3 msh
vnd Dl msh row 1
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Reciprocal Patterning of the Ectoderm by Sog and Dpp
2) A BMP repression gradient forms within the neuroectoderm -> Three rows of neuroblasts. msh ind vnd Neuroectoderm 1) A Sog gradient creates an inverse BMP activation gradient dorsally -> Epidermal Ectoderm vs. Amnioserosa. Epidermal Ectoderm A.S. race [Dpp] [Sog] Relative BMPActivity Sog Dpp V D
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