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