Loss of function in rpms-1 does not enhance phenotypes of rpm-1 mutants

The <i>C. elegans</i> E3 ubiquitin ligase RPM-1 consists of 3,766 amino acids, with a RING finger domain at the C-terminus that functions to target the DLK-1 kinase for degradation for synapse development and axon termination. <i>rpms-1 (</i> for <i>rpm-1 short,</i> aka F07B7.12 <i>)</i> resides 35 kb away from <i>rpm-1</i> on chromosome V, and is a near-perfect 12 kb duplication of <i>rpm-1 ,</i> including the entire promoter region and coding sequences. RPMS-1 consists of 1,964 amino acids and is identical to the N-terminal half of RPM-1 , except the last 40 amino acids. Previous studies showed that transgenic overexpression of the duplicated region of <i>rpm-1 (+)</i> did not rescue synapse defects of <i>rpm-1</i> loss of function mutants. Here, using CRISPR editing, we generated a double knockout of <i>rpm-1</i> and <i>rpms-1</i> . We find that axon and synapse defects in <i>rpm-1rpms-1</i> double mutants resemble those in <i>rpm-1</i> single mutants. Expression levels of endogenously tagged DLK-1 protein are increased to a comparable degree in <i>rpm-1</i> and <i>rpm-1rpms-1</i> mutants, compared to the control. These data, along with previous transgene expression analysis, support the idea that <i>rpms-1</i> does not have a major role in RPM-1-mediated cellular processes.