Investigating the molecular mechanisms that underlie tiling in Drosophila R7 photoreceptors Jennifer 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

Synapse Formation 1. filopodia search 2. cell adhesion stabilizes 3. pre-synaptic components accumulate 4. post-synaptic assembly

R7 axons require an Activin signal to tile Wild-type R7s imp  3 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 necessary for the tiling defect

Necessary Not necessary Approach 1: test whether synapse formation is necessary for the tiling defect

Create syd-1, imp  3 R7s Wild type imp  3 mutant: tiling defect imp  3, syd-1 double mutant: ????? syd-1 mutant: cannot form synapses

imp  3 syd-1 Test for non-complementation Create a syd-1, imp  3 double mutantchromosome syd-1 Bal x imp  3 Bal x imp  3 syd-1 Bal

syd-1, imp  3 has 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 FRT82drsy-1(Del) Bal x x drsy-1(Del) FRT82 Bal FRT82drsy-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 University of Oregon SPUR Program Dr. Peter O’Day Chelsie Fish Other SPUR Interns!