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

Abstract

The C. elegans 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. rpms-1 ( for rpm-1 short, aka F07B7.12 ) resides 35 kb away from rpm-1 on chromosome V, and is a near-perfect 12 kb duplication of rpm-1 , 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 rpm-1 (+) did not rescue synapse defects of rpm-1 loss of function mutants. Here, using CRISPR editing, we generated a double knockout of rpm-1 and rpms-1 . We find that axon and synapse defects in rpm-1rpms-1 double mutants resemble those in rpm-1 single mutants. Expression levels of endogenously tagged DLK-1 protein are increased to a comparable degree in rpm-1 and rpm-1rpms-1 mutants, compared to the control. These data, along with previous transgene expression analysis, support the idea that rpms-1 does not have a major role in RPM-1-mediated cellular processes.