rpm-1, a conserved neuronal gene that regulates targeting and synaptogenesis in C-elegans

Little is known of mechanisms regulating presynaptic differentiation. We id entified rpm-1 in a screen for mutants with defects in patterning of a pres ynaptic marker at certain interneuronal synapses. The predicted RPM-1 prote in contains zinc binding, RCC1, and other conserved motifs. In rpm-1 mutant s, mechanosensory neurons fail to accumulate tagged vesicles, retract synap tic branches, and ectopically extend axons. Some motor neurons branch and o vergrow; others show altered synaptic organization. Expression of RPM-1 in the presynaptic mechanosensory neurons is sufficient to rescue phenotypes i n these cells. Certain rpm-1 phenotypes are temperature sensitive, revealin g that RPM-1 function can be bypassed by maintaining mutants at the permiss ive temperature at stages commensurate with synapse formation in wild-type animals. These results indicate that RPM-1 functions cell autonomously duri ng synaptogenesis to regulate neuronal morphology.