The RNA-binding protein NOVA-1 regulates circRNA expression, alternative splicing, and aging in <i>Caenorhabditis elegans</i>

Circular RNA (circRNA) biogenesis is regulated by RNA-binding proteins (RBPs) that alter back-splicing of exons in protein coding genes. However, few in vivo roles for RBPs in the regulation of circRNA biogenesis have been characterized. We previously showed that many circRNAs increase with age in C. elegans, and that loss of circ-crh-1, an abundant age-accumulated circRNA, extends mean lifespan. Given the established role of the mammalian RBP NOVA2 in promoting circRNA biogenesis, we investigated whether nova-1, the sole C. elegans homolog of NOVA1/2, similarly regulates circRNA expression and function in vivo. RNA-sequencing of nova-1 mutants compared to wild-type identified 686 circRNAs. Of these, 103 were differentially expressed in nova-1 mutants compared to wild-type, with 76 upregulated and 27 downregulated circRNAs, suggesting NOVA-1 acts as a negative regulator of a subset of circRNAs. nova-1 mutants also exhibited linear alternative splicing changes, primarily in alternative 3' splice site usage and exon skipping, and showed minimal overlap with circRNA loci. Notably, circ-crh-1 represented a shared regulatory target, suggesting NOVA-1 may coordinate splicing regulation with the production of crh-1 circRNAs. Motif analysis further revealed that over half of the NOVA-1-regulated splicing events contained YCAY motif sites, with crh-1 harboring a high density of sites, consistent with its alternative 3' splice site usage and circRNA production. Finally, nova-1 mutants exhibited an extended mean lifespan and enhanced heat stress recovery. Together, these findings identify NOVA-1 as a key regulator of circRNA expression and alternative splicing in C. elegans, with likely downstream consequences for organismal lifespan and stress resilience.