Position-encoding molecules and the development of retinal maps

Abstract

Molecules that encode position in the retina and a principal target, the optic tectum of frogs, fish and chicks, or its mammalian homologue, the superior colliculus, are hypothesized to control the development of topographic connections by restricting the growth of retinal ganglion cell axons to topographically correct locations in the target. The normal topographic targeting of developing retinal axons is consistent with this concept in frogs and fish, and in chicks it is consistent at the coarse level of matching appropriate retinal and tectal halves. In rats, however, molecules postulated to encode rostral-caudal position do not effectively guide or restrict the growth of retinal axons to topographically appropriate regions of the SC, but seem to contribute to map formation by promoting topographic specificity in branch and arbor formation.