Drosophila timescales (at 25°C): 3 hrs: cellular blastoderm with 5000 cells
with all cells’ identities specified24 hrs: embryo hatches as feeding larva
•Movies:–QT Drosophila Development -different views: embryogenesis –SEM morph
–QT Drosophila embryogenesis –QT Drosophila Cleavage: following Histone-GFP
–QT Drosophila Gastrulation: following Histone-GFP
Drosophila – 2 lectures (½ – 1- ½ )
• Cleavage
• View -gastrulation, organogen. frame metamorph.
• Once we know the embryo, meet the molecules• Because this is a largely ‘solved’ system
• Because these genes have key roles in all metazoans
• EVERY one of 5000 cleavage state cell has a D/V and A/P ‘molecular address’, and is therefore specified.
Bicoid mRNA 1. Bicoid RNA ‘caught’ at the ‘entrance’
2. Unanchored Bicoid RNA returned to the anterior side by dynein on MTs
Bicoid mRNA-binding protein
Gap genes are turned on in broad stripes by maternal genes, each other. ALL TFs.
Hunchback
Gt
Kr
kn
hb (later)
Gap genes are turned on in broad stripes by maternal genes, each other
Pair rule genes are turned on in 7 stripes each, harder to conceptualize
Each stripe has its own enhancer, responding to a different combinatorial of Gap and Maternal proteins
Gap genes are turned on in broad stripes by maternal genes, each other
Pair rule genes are all Trascription Factors too – turn on Segment Polarity gene expression
The embryoNow has twoAdjacent organizersWhich release a
Morphogen
From syncitium withGradient of 1 (or 2)Morphogens, to seriesOf segments, each
With 2 morphogens
After the activity of four different pathways, the D/V patterning of the ectoderm Is controlled by a conserved Ser/Thr receptor that is dependent on the gradient of its ligand dpp and dpp’s interactors
D/V: An evolutionarilyConserved mechanism
dpp/BMP-4
Figure 23.14 Homologous Pathways Specifying Neural Ectoderm in Protostomes (Drosophila) and Deuterostomes (Xenopus) D/V
Gastrulation - Drosophila
http://www.flybase.org/data/images/Animation/
AND Course Site (Movies)
I. RTK pathway Sets follicle cell D/V state
II. Proteolytic cascade Sets embryos’ cell D/V state
III. Toll/Cactus/Doral Sets nuclear D/V state
IV. Dorsal TF thresholds Diff. pathway per D/V address
4 STAGES OF ESTABLISHING DORSAL/VENTRAL – 4 SEQUENTIAL PATHWAYS +
STAGE PATHWAY PATHWAY OUTCOME
I. RTK pathway Sets follicle cell D/V state
II. Proteolytic cascade Sets embryos’ cell D/V state
III. Toll/Cactus/Doral Sets nuclear D/V state
IV. Dorsal TF thresholds Diff. pathway per D/V address
4 STAGES OF ESTABLISHING DORSAL/VENTRAL – 4 SEQUENTIAL PATHWAYS +
STAGE PATHWAY PATHWAY OUTCOME
Lateral inhibition in neurectoderm to specify neruogenesis: Notch mediated
All Rhomboid expressing cells express Notch, then undergo a stochastic process for ¼ cells to become neuronal
Key factor for Dorsal identities inDrosophila
Key factor for D-V identities inVertebrates
TGF-Beta family
After the activity of four different pathways, the D/V patterning of the ectoderm Is controlled by a conserved Ser/Thr receptor that is dependent on the gradient of its ligand dpp and dpp’s interactors
D/V: An evolutionarilyConserved mechanism
dpp/BMP-4
Figure 23.14 Homologous Pathways Specifying Neural Ectoderm in Protostomes (Drosophila) and Deuterostomes (Xenopus) D/V
The course primarily addresses development of urbilaterian descendents. All reflect on the ancestor-differences are details.
So now we’ve defined both axes
in Drosophila, includingevery cell of 5000.
msh, ind, and sogmark specific D/V cells/coordinates
Subsequent to A/P specification through segmentation gene action, the Homeotic genes then allow unique functions for each segment.
Figure 6.16 Scanning Electron Micrograph of a Compound Eye in Drosophila
Eye disc patterning controlled by ‘reuse’ of the pathways seen in general axis specification
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