Showcase of Undergraduate Research and Creative Endeavors (SOURCE)

The Effect of Semaphorin 3A on Chick Embryo Retinal Growth Cones

Richardson Ballroom – DiGiorgio Campus Center

Semaphorin 3A (Sema3A) is a crucial axon guidance cue in the nervous system during embryonic development. Axon guidance molecules interact with growth cones, extensions of growing or regenerating axons supported by microfilaments looking for their synaptic targets, in this case, the brain. Some inhibitory axon guidance molecules are known to cause growth cone collapse; Sema3A is one of them. When growth cones collapse, they cease to move and then retract, often turning away from inhibitory molecules. Sema3A has been shown to be important for axon guidance in the spinal cord. Luo et al. (1993) demonstrated that Sema3A causes growth cone collapse of chick embryo dorsal root ganglion cells (DRGs), but they stated that it did not cause growth cone collapse of chick retinal ganglion cells (RGCs). We have found preliminary evidence that Sema3A does cause growth cone collapse of embryonic chick retinal ganglion cells, which is inconsistent with the Luo et al. (1993) finding. We are investigating this inconsistency; one hypothesis is that the treatment times in the previous study were not optimal. We are further testing the effect of Sema3A on RGCs using time-lapse microscopy to examine growth cone responses to Sema3A. Furthermore, we are employing a quantitative growth cone collapse assay to investigate the concentration dependence as well as treatment times to verify and extend our preliminary data.