A neural tetraspanin, encoded by late bloomer, that facilitates synapse formation.

Upon contacting its postsynaptic target, a neuronal growth cone transforms into a presynaptic terminal. A membrane component on the growth cone that facilitates synapse formation was identified by means of a complementary DNA-based screen followed by genetic analysis. The late bloomer (lbl) gene in Drosophila encodes a member of the tetraspanin family 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, but synapse formation is delayed and neighboring motoneurons display an increase in ectopic sprouting.