CELL-CONTACT-DEPENDENT SIGNALING IN AXON GROWTH AND GUIDANCE - EPH RECEPTOR TYROSINE KINASES AND RECEPTOR PROTEIN-TYROSINE-PHOSPHATASE-BETA

The growth and guidance of axons involves the recognition of complex e nvironmental cues by receptor proteins on the surface of the growth co ne and their interpretation by cellular machinery, leading to changes in cellular behaviour, Recent advances have demonstrated that the liga nds for Eph receptor tyrosine kinases, the ephrins, act as repulsive a xon guidance cues, and that Eph receptors are required for correct axo nal navigation in vivo. Members of the receptor protein tyrosine phosp hatase (RPTP) family also play important roles in axon guidance and gr owth, RPTP beta and Eph receptors interact with cell-surface-bound lig ands, and there is increasing evidence that both transmembrane ephrins and contactin, a ligand for RPTP beta, may possess an intrinsic signa lling function. Thus, the cell-contact-dependent interactions between these receptors and ligands may lead to initiation of bidirectional si gnals that regulate axonal growth and migration.