Download Organogenesis

Neurulation & Organogenesis
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
Neurogenesis
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)
Acheate Expression
en = purple acheate = black stain
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)
Neurogenic Genes
• Juxtacrine signaling
molecules
• Delta (Dl) - ligand
• Notch (N) – receptor
• kuzbanian (kuz) – protease
kuz
E(spl)
Su(H)
Delta-Notch Signaling
by kuz
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
Drosophila Neurogenesis & Vertebrate
Neurogenesis Occur
Via Homologous
Pathways
Mash – mouse acheate-scute homologue
Dll-1 – delta-like 1
Delta-Notch Signaling in
Vertebrates
Drosophila Peripheral Nervous System
• proneural clusters form in imaginal discs
• proneural clusters differentiate into SOPs and
ultimately into sensory bristles
Differentiation of Sensory Bristles
SMC (sensory mother cells) also
called SOP (sensory organ
precursor)
no SMC
numb & Notch
mutations
Organogenesis
Imaginal Disc
Imaginal Discs
Initial Specification of Imaginal Discs
Wing/Haltere
Disc Primordia
Leg Disc
Primordia
Intersection of wg stripes with Dpp expressing cells
specifies discs
Patterning of Wing Discs
Anterior-Posterior specification
established by en, & hh with Dpp
at the border
Dorsal-Ventral Polarity in Wing Disc
Apterous protein (green) dorsal wing
Vestigial protein (red) ventral wing
Wing Disc
Patterning of Wing Discs
dorsal-ventral
patterning is established
by apterous & vestigial
expression with wg
establishing the border
Patterning of Wing Discs
Vestigial (green), apterous (red), wingless (purple), cubitus
interuptus (blue)
Patterning of Leg Discs
Eversion of Leg Imaginal Disc
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)
Eye Disc Specification
Twin of eyeless
(Pax6)
Eyeless
(Pax6)
Eyes absent
(eya1, 2, 3)
Sine oculus
(Six3)
dachshund
Ectopic Expression of ey
Patterning of the Eye Disc
Differentiation in the Eye Disc
A
P
Morphogenic Furrow
Progress of Morphogenetic Furrow &
Cell Specification in Its Wake
Rhabdomere Specification
Drosophila Compound Eye
800
Ommatidia
Ommatidium
20+ cells;
8 photoreceptors
12 accessory cells
Drosophila ommatidium
Go See an Ommatidium @
http://sdb.bio.purdue.edu/fly/virtomm.mov
Analysis of R7 Differentiation
through Genetic Mosaics
sev only needed in R7 for R7 differentiation
sev functions cell autonomously