Figure Homologous Pathways Specifying Neural Ectoderm in Protostomes (Drosophila) and Deuterostomes (Xenopus) D/V

Gastrulation - Drosophila AND Course Site (Movies)

I.RTK pathwaySets follicle cell D/V state II.Proteolytic cascadeSets embryos’ cell D/V state III.Toll/Cactus/DoralSets nuclear D/V state IV.Dorsal TF thresholdsDiff. pathway per D/V address 4 STAGES OF ESTABLISHING DORSAL/VENTRAL – 4 SEQUENTIAL PATHWAYS + STAGEPATHWAYPATHWAY OUTCOME

I.RTK pathwaySets follicle cell D/V state II.Proteolytic cascadeSets embryos’ cell D/V state III.Toll/Cactus/DoralSets nuclear D/V state IV.Dorsal TF thresholdsDiff. pathway per D/V address 4 STAGES OF ESTABLISHING DORSAL/VENTRAL – 4 SEQUENTIAL PATHWAYS + STAGEPATHWAYPATHWAY 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 in Drosophila Key factor for D-V identities in Vertebrates TGF-Beta family

Figure Homologous Pathways Specifying Neural Ectoderm in Protostomes (Drosophila) and Deuterostomes (Xenopus) D/V

Both axes defined in Drosophila Now 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 the P-R gene has its Own enhancer. Even-skipped gene – 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 Two morphogens/ligands/organizers in adjacent cells

No Active

The embryo Now has two Adjacent organizers Which release a Morphogen From syncitium with Gradient of 1 (or 2) Morphogens, to series Of segments, each With 2 morphogens

Both axes now defined in Drosophila, every cell of 5000.

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