MULTIPLE ROLES OF EPH-LIKE KINASES AND THEIR LIGANDS DURING DEVELOPMENT

The Eph family of tyrosine kinase receptors and their ligands have aro used much attention over the last couple of years, because of the demo nstration of their pivotal role in axon guidance and pathfinding in th e developing vertebrate central nervous system. However, the first ind ications that these receptors may play important roles during developm ent came from studies of segmentation in the early embryo. In this rev iew, we discuss the two roles that have been attributed to Eph recepto rs and their ligands (regionalisation and axon, guidance) with referen ce to the two systems in which they were originally described, viz., t he hindbrain and the retina, respectively. Furthermore, we discuss evi dence that these molecules fulfill both these functions in each of the systems analysed, the role played by members of these two families at any one time being dependent on the developmental stage at which they are expressed.