neurulation & organogenesis. neurulation neural cells originate from the neurectoderm clusters...
TRANSCRIPT
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Neurulation & Organogenesis
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Neurulation
• Neural cells originate from the neurectoderm
• Clusters of proneural cells are specified by the proneural genes
• Single neuroblasts are specified within the proneural cluster via lateral inhibition
• Proneural and neurogenic genes, respectively, regulate these specification events
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Neurogenesis
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Proneural & Neurogenic Genes
• Proneural: Achaete-Scute complex of genes (AS-C)– Achaete (ac), scute (sc), lethal of scute (lsc), asense (as)
• Neurogenic: Notch-Delta pathway– Notch (N), Delta (Dl), Enhancer of split (E(spl)), Hairless
(H), Suppressor of Hairless (Su(H)), brainiac (brn), mastermind (mam), neurlalized (neu), kuzbanian (kuz), big brain (bib)
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Acheate Expressionen = purple acheate = black stain
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Regulation of Proneural Genes
• hairy (h), gooseberry (gb), Extramacrochaete (emc) – Emc & h are inhibitory bHLH txn factors
– Gb has a homeobox
• ventral nervous system defective (vnd), engrailed (en), wingless (wg), iroquois (iro)
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Neurogenic Genes• Juxtacrine signaling
molecules
• Delta (Dl) - ligand
• Notch (N) – receptor
• kuzbanian (kuz) – protease kuz
Su(H)E(spl)
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Delta-Notch Signaling
by kuz
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Lateral Inhibition Summary• Delta and Notch are expressed in every cell in the proneural
cluster• Dl is usually slightly more highly expressed than N
• Dl activates N• N activates Su(H)• Su(H) displaces H and activates E(spl)• E(spl) inhibits AS-C genes & indirectly, Dl• Without AS-C gene products, neural differentiation is
blocked• AS-C normally activates Dl and other proneural genes
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Drosophila Neurogenesis & Vertebrate Neurogenesis Occur Via Homologous Pathways
Mash – mouse acheate-scute homologueDll-1 – delta-like 1
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Delta-Notch Signaling in Vertebrates
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Drosophila Peripheral Nervous System• proneural clusters form in imaginal discs
• proneural clusters differentiate into SOPs and ultimately into sensory bristles
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Differentiation of Sensory Bristles
numb & Notch mutations
SMC (sensory mother cells) also called SOP (sensory organ precursor)
no SMC
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OrganogenesisImaginal Disc
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Imaginal Discs
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Initial Specification of Imaginal Discs
Intersection of wg stripes with Dpp expressing cells specifies discs
Leg Disc Primordia
Wing/HaltereDisc Primordia
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Patterning of Wing Discs
Anterior-Posterior specification established by en, & hh with Dpp
at the border
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Dorsal-Ventral Polarity in Wing Disc
Apterous protein (green) dorsal wingVestigial protein (red) ventral wing
Wing Disc
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Patterning of Wing Discs
dorsal-ventral patterning is established by apterous & vestigial
expression with wg establishing the border
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Patterning of Wing DiscsVestigial (green), apterous (red), wingless (purple), cubitus
interuptus (blue)
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Patterning of Leg Discs
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Eversion of Leg Imaginal Disc
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Proximal-distal Axis in Leg Disc
Expression of txn factors in regions of leg disc specifies proximal-distal polarity distalless (dll)(red), dachshund (dac) (green), homothorax (htx) (purple)
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Eye Disc Specification
Twin of eyeless(Pax6)
Eyeless (Pax6)
Eyes absent(eya1, 2, 3)
Sine oculus(Six3)
dachshund
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Ectopic Expression of ey
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Patterning of the Eye Disc
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Differentiation in the Eye Disc
AP
Morphogenic Furrow
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Progress of Morphogenetic Furrow & Cell Specification in Its Wake
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Rhabdomere Specification
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Drosophila Compound Eye
Ommatidium 20+ cells;
8 photoreceptors12 accessory cells
800 Ommatidia
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Drosophila ommatidium
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Go See an Ommatidium @
http://sdb.bio.purdue.edu/fly/virtomm.mov
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Analysis of R7 Differentiation through Genetic Mosaics
sev only needed in R7 for R7 differentiationsev functions cell autonomously