The catalytic activity of microRNA Argonautes plays a modest role in microRNA star strand cleavage inC. elegans

Abstract Many Argonaute proteins can cleave RNA (“slicing”) as part of the microRNA-induced silencing complex (miRISC), even though miRNA-mediated target repression is generally independent of target cleavage. Here we use C. elegans to examine the role of miRNA-guided slicing in organismal development. We find that unwinding and decay of the miRNA star strand is weakly defective in the absence of slicing, with the largest effect observed in embryos. Argonaute-Like Gene 2 (ALG-2) is more dependent on slicing for unwinding than ALG-1. The miRNAs that displayed the greatest (albeit very minor) dependence on slicing for unwinding tend to form stable duplexes with their star strand, and in some cases, lowering duplex stability alleviates dependence on slicing. While a few miRNA guide strands are reduced in slicing mutants, the basis of this is unclear since changes were not dependent on EBAX-1, a factor in the Target-Directed miRNA Degradation (TDMD) pathway. Gene expression and gross phenotype were wild type in slicing mutants, indicating that 1) slicing is not required for target regulation and 2) the weak unwinding defect does not significantly reduce the pool of functional miRISC. Thus, in contrast to previous work, miRISC slicing in C. elegans is dispensable in standard laboratory conditions.