Ch9 - Ventral-Dorsal Differentiation

Question 1

Dorsal gene

Answer 1

the protein that distinguishes dorsum from ventrum is the product of the dorsal gene

Question 2

Dorsal protein

Answer 2

once translated, Dorsal protein found throughout the embryo

- how does it act as a morphogen?

Question 3

How Dorsal acts as a morphogen

Answer 3

Found throughout

• -> translocated to nuclei in ventral
• -> into nuclei, Dorsal binds to certain genes to activate/suppress transcription

Question 4

If Dorsal DOESN’T enter the nucleus

Answer 4

• 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

Question 5

Signal cascade

Answer 5

oocyte nucleus –> follicle cells

• follicular epithelium around oocyte symmetrical –> asymmetrical with signal from oocyte nucleus

Question 6

Oocyte nucleus

Answer 6

posterior –> anterior dorsal

• follicle cells more columnar-dorsal

Question 7

The dorsalizing signal from the oocyte nucleus is a product of

Answer 7

the gurken gene

Question 8

The gurken gene

Answer 8

its protein forms an anterior–>posterior gradient on the dorsal surface

Question 9

Mutation of the gurken gene =

Answer 9

ventralization of embryo and follicle cells

Question 10

Gurken signal received by

Answer 10

follicle cells through a receptor encoded by the torpedo gene

Question 11

The torpedo gene

Answer 11

encodes receptor that allows the follicle cells to receive the gurken signal

Question 12

The torpedo gene is active in

Answer 12

ovarian follicle cells, not the emrbyo

Question 13

Spatzle and toll

Answer 13

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

Question 14

The outcome of the signalling through toll

Answer 14

gradient of Dorsal protein in ventral cell nuclei

Question 15

Gradient of Dorsal protein in ventral cell nuclei established by

Answer 15

spatzle and toll interact with Cactus

Question 16

Cactus

Answer 16

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

Question 17

Removing the Cactus protein

Answer 17

• Spatzle binds Toll
• activates Pelle protein kinase
• phosphorylates Cactus protein
• Cactus degraded
• Dorsal protein can enter nucleus

Question 18

The signal transduction cascade creates a gradient of

Answer 18

Spatzle protein highest in the ventral

= gradient of Dorsal translocation into ventral cells

Question 19

Highest concentration of Dorsal in

Answer 19

the most ventral cells

Question 20

Large amounts of Dorsal protein instructs cells to become

Answer 20

mesoderm
• lesser amounts of Dorsal =
glial or ectodermal tissue

Question 21

Dorsal specifies cells to become mesoderm in 2 ways

Answer 21

1. Activates genes that make a mesodermal phenotype

2. Indirectly inhibits dorsalizing genes zen and dpp

Question 22

Dorsal specifies cells to become mesoderm by

activating genes that make a mesodermal phenotype

Answer 22

• targets = twist, snail, rhomboid

- only in nuclei with very high concentrations of Dorsal because they have don’t have a high affinity for Dorsal

Question 23

Twist protein

Answer 23

activates mesodermal genes

Question 24

Snail protein

Answer 24

represses non-mesodermal genes

Question 25

Rhomboid

Answer 25

in cells adjacent to mesoderm

Question 26

Dorsal specifies cells to become mesoderm by indirectly inhibiting dorsalizing genes sen and dpp

Answer 26

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

Question 27

Groucho

Answer 27

trancriptional repressor protein

Question 28

Deficient in zen and dpp leads to

Answer 28

no dorsal structures