Multiple roles of Eph-like kinases and their ligands during development

The Eph family of tyrosine kinase receptors and their ligands have aroused much attention over the last couple of years, because of the demonstration of their pivotal role in axon guidance and pathfinding in the developing vertebrate central nervous system. However, the first indications that these receptors may play important roles during development came from studies of segmentation in the early embryo. In this review, we discuss the two roles that have been attributed to Eph receptors and their ligands (regionalisation and axon guidance) with reference to the two systems in which they were originally described, viz., the hindbrain and the retina, respectively. Furthermore, we discuss evidence 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.