Novel expression gradients of Eph-like receptor tyrosine kinases in the developing chick retina.

Eph-like receptor tyrosine kinases have recently been identified as critical components in the development of the retinotectal system. Complementary gradients of receptors and ligands in the retina and tectum, and within the retina itself, have previously been described. Here, we present a novel centroperipheral gradient of expression for one member of this family of receptors, Cek9, suggesting that retinal patterning and axon guidance during the establishment of retinotectal projections may involve coordinate mapping along three axes. Furthermore, we show matching gradients of two cytoplasmic kinases, compatible with their putative involvement in the intracellular signaling pathways used by these receptors in the retina. We also demonstrate a dorsal to ventral expression gradient for Cek11, an Eck-like receptor, the Eph subclass previously suggested to specify positional information along the temporonasal axis.