Faculty Mentor

Dr. Eric Birgbauer


College of Arts and Sciences


Department of Biology



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During embryonic development, axons grow from the retina of the eye to the tectum of the brain which allows for visual information transfer. Axons travel to the tectum via axon pathfinding, which is influenced by axon guidance cues. Axon guidance molecules interact with the growing tips of retinal ganglion cell (RGC) axon, which are motile structures known as growth cones. Some inhibitory axon guidance molecules are known to cause a growth cone to collapse, where they cease growth and then retract, or turn away. One such inhibitory axon guidance molecule is Semaphorin 3A (Sema 3A). While Sema 3A’s importance is known in the nervous system, a study conducted by Luo et al. (1993) found that Sema 3A causes growth cone collapse of chick embryo dorsal root ganglion cells (DRGs) but not growth cone collapse in chick retinal ganglion cells (RGCs). However, we have found significant evidence that Sema 3A does indeed cause growth cone collapse of embryonic chick retinal ganglion cells, which is inconsistent with the Luo et al. (1993) finding. After further investigation, we have found that RGC’s have the ability to regenerate from collapse after a 15-20 minute treatment with Sema 3A, thus giving the illusion to Luo et at. (1993) that Sema 3A does not affect RGC’s because of the 60-minute allotted time window they used. We are currently investigating the effect of Sema 3A on different embryonic ages (E5, E6, E7, E8). We have found preliminary data that suggests that Sema 3A will give the same effect on RGC’s no matter the age.

Publication Date





This project was supported by SC INBRE grants from the National Institute of General Medical Sciences (8 P20 GM103499) of the National Institutes of Health

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

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