BRAIN VERSUS SKIN DEVELOPMENT IN FLIES LECTURE 7: BRAIN VERSUS SKIN DEVELOPMENT IN FLIES

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

Dorsal Meso Neuro Epi dpp sog dpp “sog” snail

dpp versus sog Expression

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

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

dpp- Mutant Sog Neuronal Genes Mesodermal Genes = M e s o d r m N n - c t

dpp- Mutant

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

sog- Mutant Epidermal Genes Dpp Neuronal Genes Mesodermal Genes = M e c t

sog- Mutant

The Default State of Ectoderm is Neural

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

Sog diffuses and patterns the dorsal region Embryonic Covering Epidermis Low Dpp Hi Dpp Dpp Tld Sog

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

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

Ventral Dominant Repression msh ind vnd V

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

Dpp Dl Dl Neuroectodermal patterning in a vnd- mutant msh ind X row 3 ind, msh row 1 X

Dpp Dl Dl Neuroectodermal patterning in a vnd- mutant msh ind X row 3

Dpp Dl Dl Neuroectodermal patterning in an ind- mutant msh ind X row 3 vnd Dl ind, msh row 1

Dpp Dl Dl Neuroectodermal patterning in an ind- mutant msh row 3 msh vnd Dl msh row 1

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