Investigating Semaphorin 3A as a Possible Repulsive Axon Guidance Molecule in the Chick Visual System.

During the development of the visual system, retinal ganglion cells (RGCs) must project their axons to the synaptic targets in the brain. A variety of different molecules, known as axon guidance cues, play an important role in this process. At the end of each axon there is a growth cone, a finger-like projection that detects these molecules in the environment and reacts to them. Some axon guidance cues are repulsive and cause a growth cone collapse and retraction. One such axon guidance molecule is semaphorin 3A (Sema3A), which has been shown to cause dorsal root ganglion cells (DRG) to undergo growth cone collapse in vitro. In the visual system, previous studies indicate that Sema3A leads to RGC growth cone collapse in mouse and Xenopus, but not in chick. We have analyzed this species difference and, contrary to previous literature, we have found that Sema3A treatment leads to a dose-dependent growth cone collapse of retinal axons as well as DRGs in embryonic chick. Therefore, Sema3A might play an important role during the development of the visual system