McFarlane Lab

The output cells of the retina, the RGCs, are an attractive neuronal type in which to study axon and dendrite growth. Their dendrites and axon are identified easily, emerge from opposite sides of the cell, and can be isolated experimentally from each other. In both mammals and Xenopus, RGC axons extend in a directed fashion out of the eye to form the optic nerve that enters the brain in the ventral diencephalon. The axons make three key guidance decisions within the diencephalon: 1) cross the midline at the optic chiasm, 2) make a ~45° turn in the mid-diencephalon, and 3) recognize their dorsal midbrain target - the superior colliculus in mammals (for a subset of RGCs) and the optic tectum in amphibia. At the same time as their axons enter the brain, RGCs initiate dendrites that reach targets in the inner plexiform layer - the bipolar and amacrine cell processes. The molecules that direct the trajectories of RGC axons and ensure proper topographic mapping of projections within the target have been well studied, and include members of the four main families of axon guidance molecule, as well as others.