COMPLEMENTARY GRADIENTS IN EXPRESSION AND BINDING OF ELF-1 AND MEK4 IN DEVELOPMENT OF THE TOPOGRAPHIC RETINOTECTAL PROJECTION MAP

Topographic maps with a defined spatial ordering of neuronal connectio ns are a key feature of brain organization. Such maps are believed to develop in response to complementary position-specific labels in presy naptic and postsynaptic fields. However, the complementary labeling mo lecules are not known. In the well-studied visual map of retinal axons projecting to the tectum, the labels are hypothesized to be in gradie nts, without needing large numbers of cell-specific molecules. We rece ntly cloned ELF-1 as a ligand for Eph family receptors. Here, RNA hybr idization shows matching expression gradients for ELF-1 in the tectum and its receptor Mek4 in the retina. Binding activity detected with al kaline phosphatase fusions of ELF-1 and Mek4 also reveals gradients an d provides direct evidence for molecular complementarity of gradients in reciprocal fields, ELF-1 and Mek4 may therefore play roles in retin otectal development and have properties predicted of topographic mappi ng labels.