In addition to its expression on subsets of axons, grasshopper Semaphorin I (Sema I, previously called Fasciclin [Fas] IV) is expressed on an epithelial stripe in the limb bud, where it functions in the guidance of two sensory growth cones as they abruptly turn upon encountering this sema I boundary. We report here on the cloning and characterization of two sema genes in Drosophila, one in human, and the identification of two related viral sequences, all of which encode proteins with conserved Semaphorin domains. Drosophila sema (D-Sema) I is a transmembrane protein, while D-Sema II and human Sema III are putative secreted proteins that are similar to the recently reported chick collapsin. D-Sema I and D-Sema II are expressed by subsets of neurons and muscles. Genetic analysis in Drosophila reveals that semall is an essential gene that is required for both proper adult behavior and survival.
Bibliographical noteFunding Information:
with sequencing; Kevin Mitchell for help aligning the viral sequences and Marcia Barinaga for help interpreting them; Kai Zinn, Eldon Ball, Robin Denell, and James Truman for supplying various insect DNAs, cDNA libraries, and embryos; Robert Holmgren for the anti+-gal antibody; Todd Laverty for confirmation of cytological positions; and David Van Vactor for comments on the manuscript. We also thank the Drosophila Genome Center for the mapped P element insertion lines. A. L. K. and D. J. M. were supported by National Institutes of Health grant NS 18366. C. S. G. is an Investigator with the Howard Hughes Medical Institute.