Differential roles for CLA-1L and UNC-10 in endosomal maturation and peptide release at C. elegans synapses impacting...

Caenorhabditis elegans encode two synaptic proteins linked to the Rim/Piccolo/Fife-family, through conserved motifs: 1) Clarinet (CLA-1), has 3 isoforms (short(S), medium(M) and long(L)) that are anchored at the active zone through a common C-terminal domain and 2) UNC-10/Rim that is also highly enriched at the presynaptic density. Both the cla-1 and unc-10 mutants have demonstrable effects on synaptic transmission and in combination produce a synergistic impact that virtually eliminates synaptic transmission and that has yet to be fully understood. Recently, CLA-1L and UNC-10 were shown to differentially regulate key active zone components, culminating in reduced Ca²⁺ channels and UNC-13 levels, but these changes cannot account for the severity of the release defects in the double mutants. CLA-1L extends far beyond the synaptic active zone and has been implicated in recycling of the key autophagy protein ATG-9. In this study, we show that cla-1L and unc-10 mutants negatively impact proteins involved in endocytic processing (ITSN-1 and AP-2) and endolysosomal maturation (RAB-5 and RAB-7). These abnormalities correlate with an accumulation of synaptic pleiomorphic vesicles by EM, in both cla-1L and unc-10 mutants. In addition, unc-10 mutants accumulate dense core vesicles, due to a dramatic reduction in neuropeptide release. These observations are accompanied by significant decreases in lifespan in both cla-1L and unc-10 mutants, which are exacerbated in the double mutants. Together these data suggest that the cumulative effects on synaptic transmission that result from distinct roles of CLA-1L and UNC-10 have an impact on survival.