Investigating the molecular mechanisms that underlie tiling in

Drosophila R7 photoreceptorsJennifer Salamé

George Fox University

Topographical maps: a major principle of organization in the nervous system

cell body

synapse

These synapses do not overlap (i.e. are "tiled").

Human retina is an example of a topographical map

Fly R7 photoreceptors: a great model to study tiling

Neuron circuit development occurs through two steps: axon pathfinding and synapse formation

Neuron circuit development occurs through two steps: axon pathfinding and synapse formation

Synapse Formation

1. filopodia search 2. cell adhesion stabilizes

3. pre-synaptic componentsaccumulate

4. post-synaptic assembly

R7 axons require an Activin signal to tile

Wild-type R7s imp3 mutant R7s

Test the hypothesis that excessive synapse formation causes the tiling defect

Test the hypothesis that excessive synapse formation causes the tiling defect

Excessive synapse formation

Axon pathfinding error

Necessary

Approach 1: test whether synapse formation is necessaryfor the tiling defect

Necessary

Not necessary

Approach 1: test whether synapse formation is necessaryfor the tiling defect

Create syd-1, imp3 R7s

Wild type

imp3 mutant:tiling defect

imp3, syd-1double mutant:?????

syd-1 mutant:cannot form synapses

imp3

syd-1

Test for non-complementation

Create a syd-1, imp3 double mutantchromosome

syd-1

Bal

xBal

imp3 Bal

Bal

x

imp3 syd-1

Bal

syd-1, imp3 has a tiling defect

Approach 2: test whether excessive synapse formation is sufficient to cause a tiling defect

Approach 2: test whether excessive synapse formation is sufficient to cause a tiling defect

yes sufficient

not sufficient

C. elegans rsy-1 mutant neurons form excessive synapses

Create drsy-1 mutant R7s in Drosophila

FRT82 drsy-1(Del)

Bal

x

xdrsy-1(Del)

FRT82 Bal

Bal

FRT82 drsy-1(Del)

Bal

Test with PCR and eye color

FRT82 Positive Control Candidates

Bal

drsy-1 mutants do not have a tiling defect

Effect on synapse formation of drsy-1 mutation is inconclusive

Conclusions• Synapse formation is not necessary for a tiling defect• Excessive synapse formation may not be sufficient to

cause a tiling defect• Disrupting Activin pathway seems to affect axon

pathfinding

Axon pathfinding error

Future Research Directions

• Quantify synapses in drsy-1 mutants• Quantify synapses in tiling defect mutants• Identify genes regulated by Activin pathway in

R7s

Acknowledgments

• UO Institute of Molecular Biology

• Dr. Tory Herman• Jennifer Jeffress• Erik Lyons• Jon Kniss• Scott Holbrook

•U

niversity of Oregon SPU

R Program

•D

r. Peter O’D

ay

•Chelsie Fish

•O

ther SPUR Interns!