RESUMEN
Little is known of mechanisms regulating presynaptic differentiation. We identified rpm-1 in a screen for mutants with defects in patterning of a presynaptic marker at certain interneuronal synapses. The predicted RPM-1 protein contains zinc binding, RCC1, and other conserved motifs. In rpm-1 mutants, mechanosensory neurons fail to accumulate tagged vesicles, retract synaptic branches, and ectopically extend axons. Some motor neurons branch and overgrow; others show altered synaptic organization. Expression of RPM-1 in the presynaptic mechanosensory neurons is sufficient to rescue phenotypes in these cells. Certain rpm-1 phenotypes are temperature sensitive, revealing that RPM-1 function can be bypassed by maintaining mutants at the permissive temperature at stages commensurate with synapse formation in wild-type animals. These results indicate that RPM-1 functions cell autonomously during synaptogenesis to regulate neuronal morphology.
Asunto(s)
Proteínas de Caenorhabditis elegans , Caenorhabditis elegans/genética , Caenorhabditis elegans/fisiología , Marcación de Gen , Factores de Intercambio de Guanina Nucleótido/genética , Factores de Intercambio de Guanina Nucleótido/fisiología , Neuronas/fisiología , Sinapsis/fisiología , Animales , Caenorhabditis elegans/anatomía & histología , Secuencia Conservada/genética , Factores de Intercambio de Guanina Nucleótido/metabolismo , Mecanorreceptores/fisiología , Datos de Secuencia Molecular , Neuronas Motoras/ultraestructura , Mutación/fisiología , Neuronas/metabolismo , Sinapsis/ultraestructura , Vesículas Sinápticas/ultraestructura , TemperaturaRESUMEN
Rim1 was previously identified as a Rab3 effector localized to the presynaptic active zone in vertebrates. Here we demonstrate that C. elegans unc-10 mutants lacking Rim are viable, but exhibit behavioral and physiological defects that are more severe than those of Rab3 mutants. Rim is localized to synaptic sites in C. elegans, but the ultrastructure of the presynaptic densities is normal in Rim mutants. Moreover, normal levels of docked synaptic vesicles were observed in mutants, suggesting that Rim is not involved in the docking process. The level of fusion competent vesicles at release sites was reduced fivefold in Rim mutants, but calcium sensitivity of release events was unchanged. Furthermore, expression of a constitutively open form of syntaxin suppressed the physiological defects of Rim mutants, suggesting Rim normally acts to regulate conformational changes in syntaxin. These data suggest Rim acts after vesicle docking likely via regulating priming.