A NEURAL TETRASPANIN, ENCODED BY LATE BLOOMER, THAT FACILITATES SYNAPSE FORMATION

Upon contacting its postsynaptic target, a neuronal growth cone transf orms into a presynaptic terminal. A membrane component on the growth c one that facilitates synapse formation was identified by means of a co mplementary DNA-based screen followed by genetic analysis. The late bl oomer (lbl) gene in Drosophila encodes a member of the tetraspanin fam ily of cell surface proteins. LBL protein is transiently expressed on motor axons, growth cones, and terminal arbors. In lbl mutant embryos, the growth cone of the RP3 motoneuron contacts its target muscles, bu t synapse formation is delayed and neighboring motoneurons display an increase in ectopic sprouting.