Ch9 - Ventral-Dorsal Differentiation Flashcards
Dorsal gene
the protein that distinguishes dorsum from ventrum is the product of the dorsal gene
Dorsal protein
once translated, Dorsal protein found throughout the embryo
- how does it act as a morphogen?
How Dorsal acts as a morphogen
Found throughout
- -> translocated to nuclei in ventral
- -> into nuclei, Dorsal binds to certain genes to activate/suppress transcription
If Dorsal DOESN’T enter the nucleus
• genes responsible for ventral cell types (snail and twist) AREN’T TRANSCRIBED
• genes responsible for specifying dorsal cell types (dpp and zerknullt) AREN’T EXPRESSED
==> all cells in embryo specified as dorsal cells
(ALL VENTRAL = dorsal protein in every cell
Signal cascade
oocyte nucleus –> follicle cells
• follicular epithelium around oocyte symmetrical –> asymmetrical with signal from oocyte nucleus
Oocyte nucleus
posterior –> anterior dorsal
• follicle cells more columnar-dorsal
The dorsalizing signal from the oocyte nucleus is a product of
the gurken gene
The gurken gene
its protein forms an anterior–>posterior gradient on the dorsal surface
Mutation of the gurken gene =
ventralization of embryo and follicle cells
Gurken signal received by
follicle cells through a receptor encoded by the torpedo gene
The torpedo gene
encodes receptor that allows the follicle cells to receive the gurken signal
The torpedo gene is active in
ovarian follicle cells, not the emrbyo
Spatzle and toll
Spatzle (produced on ventral side) cleaved
–> binds product of toll gene
• activated by Spatzle = proteins on ventral side
transduces signal into cell on VENTRAL - not dorsal
The outcome of the signalling through toll
gradient of Dorsal protein in ventral cell nuclei
Gradient of Dorsal protein in ventral cell nuclei established by
spatzle and toll interact with Cactus
Cactus
protein that blocks the part of Dorsal protein that lets dorsal into the nuclei =
whole signalling system to split Cactus from Dorsal in the ventral part of the embryo
Removing the Cactus protein
- Spatzle binds Toll
- activates Pelle protein kinase
- phosphorylates Cactus protein
- Cactus degraded
- Dorsal protein can enter nucleus
The signal transduction cascade creates a gradient of
Spatzle protein highest in the ventral
= gradient of Dorsal translocation into ventral cells
Highest concentration of Dorsal in
the most ventral cells
Large amounts of Dorsal protein instructs cells to become
mesoderm
• lesser amounts of Dorsal =
glial or ectodermal tissue
Dorsal specifies cells to become mesoderm in 2 ways
- Activates genes that make a mesodermal phenotype
2. Indirectly inhibits dorsalizing genes zen and dpp
Dorsal specifies cells to become mesoderm by
activating genes that make a mesodermal phenotype
• targets = twist, snail, rhomboid
- only in nuclei with very high concentrations of Dorsal because they have don’t have a high affinity for Dorsal
Twist protein
activates mesodermal genes
Snail protein
represses non-mesodermal genes
Rhomboid
in cells adjacent to mesoderm
Dorsal specifies cells to become mesoderm by indirectly inhibiting dorsalizing genes sen and dpp
depends on structures of genes’ enhancers (activate/repress)
• zen enhancer has a silencer with a binding site for Dorsal and a second site for 2 other DNA binding proteins
- these 2 proteins enable Dorsal to bind a transcriptional repressor protein (Groucho) and bring it to the DNA
Groucho
trancriptional repressor protein
Deficient in zen and dpp leads to
no dorsal structures
