Identification and characterization of roundabout orthologs in zebrafish

The Roundabout (Robo) family of receptors and their extracellular ligands, the Slit protein family, play important roles in repulsive axon guidance. F irst identified in Drosophila. Robe receptors form an evolutionarily conser ved sub-family of the immunoglobulin (Ig) superfamily that are characterize d by the presence of five Ig repeats and three fibronectin-type ill repeats in the extracellular domain, a transmembrane domain, and a cytoplasmic dom ain with several conserved motifs that play important roles in Robo-mediate d signaling (Cell 92 (1998) 205; Cell 101 (2000) 703). Robe family members have now been identified in C. elegans, Xenopus, rat, mouse, and human (Cel l 92 (1998) 205; Cell 92 (1998) 217: Cell 96 (1999) 807: Dev. Biol. 207 (19 99) 62). Furthermore, multiple robo genes have been described in Drosophila , rat. mouse and humans, raising the possibility of potential redundancy an d diversity in robo gene function. As a first step in elucidating the role of Robe receptors during vertebrate development, we identified and characte rized two Robe family members from zebrafish. We named these zebrafish gene s robo1 and robo3, reflecting their amino acid sequence similarity to other vertebrate robe genes. Both genes are dynamically expressed in the develop ing nervous system in distinct patterns. robo3 is expressed during the firs t day of development in the hindbrain and spinal cord and is later expresse d in the tectum and retina. robo1 nervous system expression appears later i n development and is more restricted. Moreover, both gents are expressed in non-neuronal tissues consistent with additional roles for these genes duri ng development. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.