RESUMO
The proper display of transmembrane receptors on the leading edge of migrating cells and cell extensions is essential for their response to guidance cues. We previously discovered that MADD-4, which is an ADAMTSL secreted by motor neurons in Caenorhabditis elegans, interacts with an UNC-40/EVA-1 co-receptor complex on muscles to attract plasma membrane extensions called muscle arms. In nematodes, the muscle arm termini harbor the post-synaptic elements of the neuromuscular junction. Through a forward genetic screen for mutants with disrupted muscle arm extension, we discovered that a LAMMER kinase, which we call MADD-3, is required for the proper display of the EVA-1 receptor on the muscle's plasma membrane. Without MADD-3, EVA-1 levels decrease concomitantly with a reduction of the late-endosomal marker RAB-7. Through a genetic suppressor screen, we found that the levels of EVA-1 and RAB-7 can be restored in madd-3 mutants by eliminating the function of a p38 MAP kinase pathway. We also found that EVA-1 and RAB-7 will accumulate in madd-3 mutants upon disrupting CUP-5, which is a mucolipin ortholog required for proper lysosome function. Together, our data suggests that the MADD-3 LAMMER kinase antagonizes the p38-mediated endosomal trafficking of EVA-1 to the lysosome. In this way, MADD-3 ensures that sufficient levels of EVA-1 are present to guide muscle arm extension towards the source of the MADD-4 guidance cue.
Assuntos
Proteínas de Caenorhabditis elegans/metabolismo , Caenorhabditis elegans/metabolismo , Proteínas de Transporte/metabolismo , Proteínas Quinases p38 Ativadas por Mitógeno/metabolismo , Proteínas rab de Ligação ao GTP/metabolismo , Animais , Caenorhabditis elegans/enzimologia , Proteínas de Caenorhabditis elegans/genética , Moléculas de Adesão Celular/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Lisossomos/metabolismo , Sistema de Sinalização das MAP Quinases , Proteínas de Membrana/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Netrinas , Junção Neuromuscular/fisiologia , Transporte Proteico/fisiologia , Proteínas Quinases p38 Ativadas por Mitógeno/genéticaRESUMO
The netrins and slits are two families of widely conserved cues that guide axons and cells along the dorsal-ventral (D-V) axis of animals. These cues typically emanate from the dorsal or ventral midlines and provide spatial information to migrating cells by forming gradients along the D-V axis. Some cell types, however, extend processes to both the dorsal and ventral midlines, suggesting the existence of additional guidance cues that are secreted from both midlines. Here, we report that a previously uncharacterized protein called MADD-4 is secreted by the dorsal and ventral nerve cords of the nematode C. elegans to attract sensory axons and muscle membrane extensions called muscle arms. MADD-4's activity is dependent on UNC-40/DCC, a netrin receptor, which functions cell-autonomously to direct membrane extension. The biological role of MADD-4 orthologs, including ADAMTSL1 and 3 in mammals, is unknown. MADD-4 may therefore represent the founding member of a family of guidance proteins.