Acts as a calcium-dependent, homophilic cell adhesion molecule that regulates neural recognition during the development of the nervous system. Component of the repulsive Plexin signaling response to regulate motor axon guidance at the embryonic stage. Also component of a receptor complex that is required in the adult visual system to innervate the lamina layer; specific targeting of R1-R6 axons. Interacts with plexA; component of a receptor complex that mediates the repulsive signaling in response to Semaphorin ligands. Dynamically expressed during embryogenesis in several areas of the developing nervous system, including neurons and fasciculating axons. Expression in stage 7 embryos is seen in the anterior midgut primordia, cephalic furrow and along the germinal band. At stage 11, expression is in 15 stripes over the trunk region, and in the anterior and posterior midgut primordia. Stage 12 shows expression in the developing nervous system, procephalic lobe and maxillar bud. Stage 13 shows expression in the ventral cord, maxillar segment and in three regions of the gut. At stage 16 expression is preferentially detected throughout the nervous system, including the neuromers in the ventral cord and the supraesophageal ganglion (at protein level). In larva, expression is seen in developing R cells and is localized predominantly to R1-R6 growth cones. Expressed both maternally and zygotically, during early to mid embryogenesis and early pupation. Axon guidance defects. R-cell differentiation and cell fate determination are normal, but many R1-R6 axons connect abnormally to medulla instead of innervating lamina. Belongs to the protein kinase superfamily. Tyr protein kinase family. Insulin receptor subfamily. This protein has been proposed to undergo autophosphorylation on tyrosine residues which is induced in response to cell adhesion (PubMed:1371458). However, as mammalian orthologs of this protein seem to lack kinase activity this protein may associate with, and be phosphorylated by, an unknown active tyrosine kinase.