Showcase of Undergraduate Research and Creative Endeavors (SOURCE)

The Response of Chick Retinal Ganglion Cells to Semaphorin 3A: potential Semaphorin 3A receptors and effects of BDNF and CNTF

In the developing nervous system, axons are guided towards their targets by guidance cues. The guidance molecule Semaphorin 3A is a repulsive axon guidance molecule for many axons. Previously, it was found that Semaphorin 3A didn’t cause collapse of chick retinal ganglion cell (RGC) growth cones. Contrary to original findings, we found the addition of Semaphorin 3A induced the collapse of RGC growth cones in a dose-dependent manner. One hypothesis is that the difference in results may be due to the presence of neurotrophins, which in some axons increases the sensitivity of the growth cones to semaphorin. We examined the response of chick RGC growth cones to Semaphorin 3A to see if they can be modulated by exposure to neurotrophins BDNF and CNTF. RGCs cultured with BDNF and CNTF did not have increased growth cone collapse activity compared to the control. Thus, chick RGC growth cones collapse when treated with Semaphorin 3A and BDNF and CNTF do not factor into that collapse. Since RGCs are responding to Semaphorin 3A, then Semaphorin 3A receptor(s) have to be expressed. Semaphorin 3A has multiple known receptors and accessory receptors. However, not much is known about the Semaphorin 3A receptors expressed during chick retinal development. Preliminary results indicate that Neuropilin 2, Plexin A1, Plexin A2, and Plexin B2 are expressed throughout chick retinal development while Neuropilin 1, Plexin A4, L1 CAM, and CHL1 expression varies depending on developmental stage. These findings indicate that Semaphorin 3A may be a repulsive guidance molecule for RGCs potentially acting though multiple receptors.