THE EPHRINS AND EPH RECEPTORS IN NEURAL DEVELOPMENT

The Eph receptors are the largest known family of receptor tyrosine ki nases. Initially all of them were identified as orphan receptors witho ut known ligands, and their specific functions were not well understoo d. During the past few years, a corresponding family of ligands has be en identified, called the ephrins, and specific functions have now bee n identified in neural development. The ephrins and Eph receptors are implicated as positional labels that may guide the development of neur al topographic maps. They have also been implicated in pathway selecti on by axons, the guidance of cell migration, and the establishment of regional pattern in the nervous system. The ligands are anchored to ce ll surfaces, and most of the functions so far identified can be interp reted as precise guidance of cell or axon movement. This large family of ligands and receptors may make a major contribution to the accurate spatial patterning of connections and cell position in the nervous sy stem.