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Threshold dependent BMP Signaling:
A Conserved Mechanism for Patterning the Ectoderm Ethan Bier Section of Cell and Developmental Biology, UCSD
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Epi Neuro Neuro Dorsal Meso snail dpp “sog” sog
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Sog blocks BMP invasion of the neuroectoderm
Mesodermal Genes Neuronal Genes Epidermal Genes Neuronal Genes BMP B r k Sog Dorsal = M e s o d r m N n - u a l E c t
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X Neural Genes are Repressed By BMP Signaling Mesodermal Genes
Neuronal Genes Sog Neuronal Genes Epidermal Genes B r k X Dpp = M e s o d r m N n - u a l E c t
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Neural Genes are Repressed By BMP Signaling
Neuronal Genes Mesodermal Genes = M e s o d r m N n - u a l E c t
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Neural Genes are Repressed By BMP Signaling
dpp- wt l’sc tkv
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X Dpp Invades the Neuroectoderm of sog- Mutants Epidermal Genes Dpp
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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Dpp Invades the Neuroectoderm of sog- Mutants
Epidermal Genes Neuronal Genes Dpp Mesodermal Genes = M e s o d r m N n - u a l E c t
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Dpp Invades the Neuroectoderm of sog- Mutants
wt sog-; Dpdpp
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The Default state of Ectoderm is Neural
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Subdivision of the neuroectoderm
Dorsal Dpp Non-neural genes Neural genes Sog B r k
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Subdivision of the neuroectoderm
Dorsal Dpp Non-neural genes Neural genes Neuronal genes Msh Ind Vnd
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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 dominance Ventral dominant repression D msh ind vnd V
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Generating lateralized embryos
ECT 3 2 NE 2 1 MES Mid-lateralized Embryos -> Uniform “ind” levels of Dorsal st2-dpp “ind”
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Gene expression in lateralized embryos
Mid-Lateralized Embryos ind msh vnd dpp Dorsal
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Localized Dpp activity along the A/P axis
sog+ sog dpp pMAD sog dpp pMAD sog-
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Subdivision of the neuroectoderm
dpp merge
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Gene expression borders shift in BMP- cells
ECT NE MES 1 3 2 st2-brk Brk Dpp st2-brk
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Dosage dependent BMP-repression in vertebrates
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BMPs can pattern lateralized vertebrate embryos
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Conserved Patterning of the Neuroectoderm?
Drosophila Neuroectoderm Nkx2.2 Gsh/Pax6 Msx1/2 BMP4 Chd Ventral Midline = Floorplate Vertebrate Neuroectoderm msh vnd ind Dpp Sog Ventral Midline
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