lec 9- patterning the dorsal ventral axis

Question 1

what maternal effect gene plays a role in the patterning of the dorsal-ventral axis?

Answer 1

Dorsal and the activation of its receptors

Question 2

how is dorsal distributed in the embryo?

Answer 2

it is distributed throughout the cytoplasm that surrounds the nuclei on the periphery of the syncytium

Question 3

what is Toll?

Answer 3

a receptor

Question 4

where is the receptor Toll located in the syncytium blastoderm?

Answer 4

on the membrane that surrounds the blastoderm, all around it

Question 5

what protein is the fragmented ligand for Toll made of?

Answer 5

Spatzle

Question 6

where is the Spatzle located in the blastoderm?

Answer 6

it is located outside the embryo in the perivitelline space and it is evenly distributed while also being inactive

Question 7

where is the proteinase that cleaves Spatzle to make ligands for Toll located?

Answer 7

on the ventral side

Question 8

once Spatzle has been cleaved and the ligands binds to Toll on the ventral side, what happens?

Answer 8

-the activated receptors send a signal to Dorsal allowing it to enter the nuclei, resulting in Dorsal protein to create a gradient and has a high concentration in ventral region while low in the dorsal.
-this means Dorsal protein activates the genes needed to specify ventral region of embryo

Question 9

what are the 3 steps for Dorsal to move into nuclei?

Answer 9

1. Dorsal is held in the cytoplasm by a protein called cactus
2. when Toll is activated by binding to the Spatzle fragment, its cytoplasmic domain binds to a protein called Tube which activates kinases
3. The kinases phosphorylate Cactus and it is then degraded, Dorsal is now able to enter the nucleus and activate genes needed to specify the ventral region of the embryo

Question 10

does Dorsal act as a morphogen?

Answer 10

yes

Question 11

what does Dorsal do once in the nuclei?

Answer 11

-acting as a morphogen, it specifies the initial pattern along the DV axis
- It turns transcription of different zygotic genes either on or off
-after the gradient is established, the embryo cellularizes and transcription factors can no longer diffuse between nuclei. This means signalling molecules and their receptors must be used to transmit signals between cells

Question 12

what is expressed where dorsal is low and what is it?

Answer 12

Decapentaplegic (Dpp), a secreted signalling molecule

Question 13

what is expressed where dorsal is high?

Answer 13

Twist

Question 14

why does it take a lot of Dorsal to activate Twist?

Answer 14

Twist has low affinity for Dorsal

Question 15

in what cells are the amnioserosa and dorsal ectoderm specified in?

Answer 15

Dpp cells

Question 16

where are the mesoderm and neurectoderm specified in?

Answer 16

Twist cells, in the ventral region where Dorsal is present

Question 17

what else is expressed with Dpp where Dorsal is low?

Answer 17

a protease called Tolloid (Tld)

Question 18

what is expressed on the side with high Dorsal where the region is specified as the neurectoderm?

Answer 18

Short gastrulation protein (Sog)

Question 19

what happens to Sog and Dpp?

Answer 19

-Sog protein is released to the outside of cells and it diffuses from the cells where it is expressed, forming a gradient
-where Sog meets Dpp, it binds to it which prevents Dpp signalling from stopping it from binding with its receptors
-As Sog diffuses towards the dorsal region, it continues to bind to Dpp, but due to Sog not being produced there, the number of unbound Dpp increases, with the most at the peak of the dorsal region
-Tld helps create more active Dpp at the peak by cleaving Sog resulting in more released Dpp which can bind to its receptors

Question 20

what are the first zygotic genes expressed that all encode transcription factors

Answer 20

gap genes

Question 21

how were the gap genes first identified?

Answer 21

by their mutant phenotypes

Question 22

what controls gap gene expression?

Answer 22

anterior-posterior gradients of maternally-expressed proteins together with interactions between the gap genes

Question 23

when the embryo is a multinucleate syncytium, what does the bicoid do?

Answer 23

initiates gap gene expression

Question 24

what gap gene does bicoid activate?

Answer 24

hunchback, which is important to turn on other gap genes

Question 25

how do we know there is a relationship between bicoid and hunchback?

Answer 25

when bicoid levels increase, so does hunchback expression

Question 26

what does the hunchback transcription factor restrict?

Answer 26

it restricts gap gene expression to stripes along the AP axis

Question 27

when is the kruppel gene activated?

Answer 27

when there are low levels of hunchback, high represses it

Question 28

if there is a very low threshold of hunchback, is kruppel gene still expressed?

Answer 28

no

Question 29

how was the role of hunchback tested?

Answer 29

when there are high levels of hunchback, the kruppel gene is pushed to the posterior, but in an embryo that lacks bicoid proteins, the hunchback gene is less and kruppel is more towards the anterior

Question 30

can gap genes also repress one another?

Answer 30

yes

Question 31

where do gap genes repress one another?

Answer 31

in regions of overlapping

Question 32

how is the anterior and the posterior side of knirps expressed?

Answer 32

the anterior is expressed below a certain hunchback threshold whilel the posterior is expressed by a similar interaction with tailless

Question 33

do gap genes divide the embryo up into broad domains?

Answer 33

yes

Question 34

is the dividing of different regions of the embryo only possible because the syncytial blastoderm allows free diffusion of transcription factors?

Answer 34

yes