Lack of CeR-2a RNA gene delays egg-laying onset in C. elegans mutant

CeR-2a RNA is a putative Caenorhabditis elegans homolog of vertebrate U8 small nucleolar RNA (snoRNA), which plays an essential role in large subunit (LSU) pre-rRNA processing. It was previously reported that, in the mutant strain MT16939, which lacks the CeR-2a RNA gene (cer-2a), there were higher levels of accumulation of the LSU pre-rRNA c'1 than in wild-type N2. To confirm this, we generated two strains using the MosSCI method: HUJ0005, in which cer-2a was reintroduced, and HUJ0006, in which cer-2b, a nearly identical paralog, was inserted. qRT-PCR analysis showed that cer-2a expression in N2 was about twice as much as that in N2. The levels of pre-rRNA c'1 were restored in both HUJ0005 and HUJ0006. Ribosome sedimentation profiling indicated an increased 40S:60S ribosomal subunit ratio in MT16939 and HUJ0007, a control strain lacking cer-2a but carrying a single cer-2b, suggesting defective rRNA maturation. Additionally, both MT16939 and HUJ0007 exhibited delayed egg-laying onset, a phenotype that was rescued in HUJ0005 and HUJ0006. Growth rates were similar among the HUJ strains, indicating that the reproductive delay in MT16939 was due to the absence of cer-2a rather than general developmental defects. These results highlighted the critical role of cer-2a in pre-rRNA processing, ribosome biogenesis, and reproductive timing in C. elegans.