comm in c axon giudance sorting of robo in vivo

Question 1

how does comm control axon guidance in drosphila?

Answer 1

Comm controls the amount of robo on the cell surface

Question 2

what is robo?

Answer 2

the receptor for slit (repellent)

Question 3

what two models have been proposed about how comm regulates robo?

Answer 3

sorting model
clearance model

in this paper these models are tested in vivo

Question 4

is comm required in midline cells for crossing?

Answer 4

no

- comm expression is not required in midline cells for crossing

Question 5

how is it seen that comm prevents delivery of robo to the growth cone?

Answer 5

robo is fused to GFP so can be visualised

- comm prevents dlivery of robo GFP to the growth cone

Question 6

what does nedd4 do?

Answer 6

ubiquitinate comm (not required for function?)

• nedd4 ligase unlikely to have a role in midline crossing

Question 7

are precrossing axons sensitive to slit?

Answer 7

no

Question 8

after crossing are axons sensitive to slit?

Answer 8

yes

- so they are unable to recross

Question 9

is comm expressed in ipsiltaeral neurons?

Answer 9

no - as these axons do not cross midline

need to be repelled from midline crossing so need to be sensitive to slits

Question 10

where is robo sorted to in the presence of comm

Answer 10

• effects sorting at trans golgi network
• sorted into late endosomes and trafficked to lysosome for degradation
• little if any robo reaches the growth cone

Question 11

what does clearance model prpose?

Answer 11

comm removes robo from the membrane

• interaction of comm in axons and comm in midline cells is supposed to restrict comm to midline segments of axons
• robo is selectively depleted from this side

Question 12

when do poxn neurons cross

Answer 12

• cross when comm is present but not in a comm null bakground
• identified by poxn-gal4
• when comm expressed in neurons rescued midline crossing even when there was no comm in midline cells
• comm in midline cells does not contirbute to crossing

Question 13

what happens when ap ipsilateral neurons are forced to express commtransgene

Answer 13

they almost always extend their axons across the midline (dont usually)

Question 14

what does com require for its function?

Answer 14

certain sequences in its ec and tmd

e.g. endosomal sorting signal

Question 15

why wa the pns looked at and not the cns?

Answer 15

cos in the cns adding or removing comm alters and axons trajectory so we dont know if any change we see in robo-gfp trafficking is due to comm expression or indirectly caused by altered path

Question 16

does comm function require its ubiquititination?

Answer 16

no

- n evidence that comm function requires ubiquitination by nedd4 ligase

Question 17

what happens to robo gfp vesicles in the axon in the prescence of comm?

Answer 17

• are less robo-gfp vesicles

- is also slower transport to axon