SEMAPHORIN-II CAN FUNCTION AS A SELECTIVE INHIBITOR OF SPECIFIC SYNAPTIC ARBORIZATIONS

Previous studies showed that grasshopper semaphorin I, a transmembrane semaphorin, functions in vivo to steer a pair of growth cones, preven t defasciculation, and inhibit branching; and that chick collapsin, a secreted semaphorin, can function in vitro to cause growth cone collap se. Semaphorin II, a secreted semaphorin in Drosophila, is transiently expressed by a single large muscle during motoneuron outgrowth and sy napse formation. To test the in vivo function of semaphorin II, we cre ated transgenic Drosophila that generate ectopic semaphorin II express ion by muscles that normally do not express it. The results show that semaphorin II can function in vivo as a selective target-derived signa l that inhibits the formation of specific synaptic terminal arbors.