Midterm 2

Question 0

Prospero (pros)

Answer 0

Transcription factor that determines GMC versus NB identity

Question 1

Localized Determinant

Answer 1

Factor that is localized to a region of the cell and then gets partitioned into only one of the two daughter cells following cell division

Example: Inscutable/Pins

Question 2

Prospero mutation

Answer 2

Ganglion mother cells cannot function properly and can’t produce neurons

Question 3

What is the difference between external sensory (ES) sop and chordotonal organ (CHO) sop?

Answer 3

Transcription factor Cut

1) Only present in ES sops
2) Cut is both necessary and sufficient to determine ES identity

Question 4

Cut Experiments

Answer 4

1) Cut- mutant: SOPs that would have given rise to ES organs now become CHO organs -> Shoes Cut is NECESSARY
2) Force Cut expression in CHO SOP, CHO is transformed into ES organs -> shoes Cut is SUFFICIENT

Question 5

ES Organ Cell Lineage

Answer 5

• Numb is assymetrically distributed in SOP forming cells IIa and IIb
• IIa and IIb form an equivalence group but IIb is usually signaling cell because it contains Numb -> Numb reduced notch signaling
• IIb signaling cell forms neuron and glial cell
• IIa received cell forms hair cell and socket cell

Question 6

Imaginal Discs

Answer 6

20 cells set aside in embryo that give rise to adult structures during metamorphosis

Question 7

Larval Development

Answer 7

Everywhere: Hh activates Dpp in cells anterior to Hh expressing cells

In eye: Dpp activates Hh -> creates a propagating positive feedback loop -> morphogenetic furrow moves across eye disc

Question 8

Fly Eye Formation

Answer 8

Starts with R8 which forms a cell cluster and divides to 3, then 5, then 7 cells

Even spacing of cells due to lateral inhibition by Notch pathway

Question 9

Boss Sevenless Signaling

Answer 9

Signal made by R8 cell called Boss

Sevenless + Boss mutants lack R7, these flies are UV blind

Question 10

Mosaic Analysis

Answer 10

Flies that are heterozygous for the Sevenless(-) mutation

• Sevenless gene function is required in R7 and R7 only
• Boss gene function is required exclusively in R8, Boss is a signal in R8 cell that activates sevenless receptor on R7 cell

Question 11

Eye Formation in Vertebrates

Answer 11

1) Eye is derived from brain

2) Cell communication drives formation of the eye

Question 12

Eye Development in Squid

Answer 12

Compared to vertebrates, structure is very similar. Development is done by different mechanism, instead of inductive mechanism, skin cells “creep” over lens of eye.
This is an example of CONVERGENT EVOLUTION: evolutionary path completely independent and separate

Question 13

Genes involved in formation of eye

Answer 13

Flies: Eyeless (Transcription factor)
Vertebrates: Pax 6 (Transcription factor)

Question 14

Evidence in favor of Eyeless/Pax 6 as an eye master gene

Answer 14

1) Pax 6 genes in all species are expressed early in the eye primordium
2) Reduction in Pax 6 gene function leads to small, or absent, eyes in flies, mice, and humans
3) Mis-expression of Pax6 in flies (Eyeless or human Pax 6) leads to ectopic eye formation

Question 15

Evidence against Eyeless/Pax 6 as an eye master gene

Answer 15

1) Pax 6 is expressed more broadly in the brain than just the eye
2) Elimination of Pax 6 function results in more severe brain defects (than just being eyeless)
3) Pax 6 can only induce eye formation in some tissues when mis-expressed
4) There are other genes that are like Pax 6

Question 16

Cell migration of axon pathfinding

Answer 16

1) Cell intrinsic characteristics determine initial direction of migration
2) A few critical choice points in navigation
3) Many of the choice points have redundant cues

Question 17

Neural crest experiment

Answer 17

1) Neural crest cells on plastic plate-> won’t migrate
2) If you coat plate with extracellular matrix molecules such as fibronectin, collagen, laminin, etc. -> more than 1 will work for cell migration, but if you include antibodies against all of them, can stop migration

Question 18

Which mutants increase/decrease cell death?

Answer 18

Increases cell death: Ced 9(-)

Decreases cell death: Egl1(-), Ced3 (-), Ced4 (-)

Question 19

Axon Extension

Answer 19

• Axon grows when filipodia pulls the growth cone due to adhesion to extracellular substrate
• Actin and myosin in growth cone regulated by small GTPases (Rho/Rac/CDC42) and steer growth cone
• Isolated growth cone continues migrating until material is used up

Question 20

Pathfinding (Grasshopper Limb System)

Answer 20

• First axon of path, Ti1, is pioneer axon and grows with help of guidepost cells (Fe1, Tr1, Cx1)
• Following axons fasciculate with pioneer axons to create axon tracks

Question 21

What happens when you remove guidepost cells?

Answer 21

Remove Cx1 -> stuck at Tx/Cr boundary
Kill Fe1 or Tr1 -> Slows down but eventually finds way
*Some guideposts are redundant cues

Question 22

What is NGF and what does it do?

Answer 22

NGF (nerve growth factor) is a tropic factor that acts via retrograde axon transport to move from axon -> cell body

Question 23

How does NGF activate live signals in cell?

Answer 23

NGF binds to TrkA (receptor tyrosine kinase with high affinity) -> MapK is activated -> moves into nuclear -> activates Bcl2, TrkA genes

Question 24

Describe 3 conditions and their results of the three chamber experiment

Answer 24

1) Neurons in central chamber and NGF in all chambers
A. Neurons survive
B. Extend axons to other chambers

2) NGF only in central chamber
A. Neurons survive
B. Extend axons only within central chamber

3) NGF only in outer chamber C
A. Neurons survive
B. Extend axons in chambers A and C but not B

Question 25

What were the conclusions of the three chamber experiment?

Answer 25

• NGF is required in cell body for survival
• NGF can be transported in a retrograde fashion from outer -> inner chamber
• NGF is required locally for axial outgrowth

Question 26

How is RTK signaling made selective?

Answer 26

1) different developmental histories if cells lead to different responses
2) timing