A Gradient of Molecules in Avian Retina with Dorsoventral Polarity

l Mechanisms that impart positional information for the assembly of the developing nervous system and the establishment of specific synaptic connections have been studied in model systems. The retina is a highly ordered laminar structure due to segregation of different classes of neuronal cell bodies and synapses into separate strata (Karten, this volume). Synaptic connections between retina ganglion neurons and tectum neurons preserve the topographic relations of ganglion neurons in the retina, resulting in a point-to-point retinotectal map. However, the mechanisms underlying these phenomena have not been defined. Sperry (1963) postulated that two orthogonal gradients of molecules on retina ganglion neurons and corresponding gradients of complementary molecules in the optic tectum might determine the specificity of connections between retina and tectum neurons. Other mechanisms that have been proposed include adhesive interactions between migrating retina neurites, myelination of bundles of retina axons, and formation of extracellular channels by glia to guide retina axons (Silver and Sidman 1980). Antisera have been widely used to study retinal structure and function (Goldschneider and Moscona 1972; Thiery et al. 1977; Hausman and Moscona 1979). Clonal neural retina hybrid cell lines derived from single retina cells [as a homogeneous immunogen) have been used to produce rabbit antiserum demonstrating an antigen of the rodent neural retina that was expressed in a restricted topographic domain (Trisler et al. 1979). Hybridoma cell lines were derived by fusing mouse myeloma cells with spleen cells from mice immunized with retina cells to produce monoclonal antibodies to retina neurons or Miiller cells (Eisenbarth et al. 1979; Barnstable 1980).