Drosophila – 2 lectures (½ – 1- ½ ) Cleavage View -gastrulation, organogen. frame metamorph....
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Transcript of Drosophila – 2 lectures (½ – 1- ½ ) Cleavage View -gastrulation, organogen. frame metamorph....
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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.
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Both axes definedin Drosophila
First to Anterior-Posterior Axis (A-P)
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Bicoid mRNA 1. Bicoid RNA ‘caught’ at the ‘entrance’
2. Unanchored Bicoid RNA returned to the anterior side by dynein on MTs
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Show:Bcd-gastrulation
Gastrulation-dorsal
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In syncitium
For control of Hunchback protein – Bicoid is a transcription factor, but Nanos . . .
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Nanos is an RNA binding protein that PREVENTS Hunchback Translation
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Gap genes are turned on in broad stripes by maternal genes, each other. ALL TFs.
Hunchback
Gt
Kr
kn
hb (later)
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Gt
Kr
kn
hb (later)
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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
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Each stripe of theP-R gene has its Own enhancer.
Even-skippedgene – 7 stripes.
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Each stripe has its own enhancer, responding to a different combinatorial of Gap and Maternal proteins
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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
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hh hh hh hh Two morphogens/ligands/organizers in adjacent cells
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No
Active
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The embryoNow has twoAdjacent organizersWhich release a
Morphogen
From syncitium withGradient of 1 (or 2)Morphogens, to seriesOf segments, each
With 2 morphogens
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Both axes definedin Drosophila,
every cell of 5000.Now to D/V
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Figure 23.14 Homologous Pathways Specifying Neural Ectoderm in Protostomes (Drosophila) and Deuterostomes (Xenopus) D/V
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Gastrulation - Drosophila
http://www.flybase.org/data/images/Animation/
AND Course Site (Movies)
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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
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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
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Dorsal fate determined in oocyte, through signaling between oocyte and somatic follicle cells
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Gurken protein on future dorsal side of oocyte, facing cells which become dorsal
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Human blood clotting cascade– Also a series of
(extracellular )proteolytic cleavages
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Dorsalized Ventralized
Ventral fates dictated by NUCLEAR presence of the protein Dorsal
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Gradient of Nuclear Dorsal protein imparts D-V IDs to cells
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Twist Protein specifies mesoderm
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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
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Lateral inhibition in neurectoderm to specify neruogenesis: Notch mediated
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Key factor for Dorsal identities inDrosophila
Key factor for D-V identities inVertebrates
TGF-Beta family
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Figure 23.14 Homologous Pathways Specifying Neural Ectoderm in Protostomes (Drosophila) and Deuterostomes (Xenopus) D/V
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All animals have related developmental histories
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out inevert
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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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Figure 6.17 Differentiation of Photoreceptors in the Drosophila Compound Eye
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Figure 6.18 Major Genes Known to be Involved in the Induction of Drosophila Photoreceptors
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