Kotagama, K. | bioRxiv Science

bioRxiv2023

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

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 genome editing in C. elegans to examine the role of miRNA-guided slicing in organismal development. In contrast to previous work, slicing-inactivating mutations did not interfere with normal development when introduced by CRISPR. We find that unwinding and decay of miRNA star strands 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 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. Gene expression changes were consistent with negligible to moderate loss of function for miRNA guides whose star strand was upregulated, suggesting a reduced proportion of mature miRISC in slicing mutants. While a few miRNA guide strands are reduced in the mutant background, the basis of this is unclear since changes were not dependent on EBAX-1, a factor in the Target-Directed miRNA Degradation (TDMD) pathway. Overall, this work defines a role for miRNA Argonaute slicing in star strand decay; future work should examine whether this role could have contributed to the selection pressure to conserve catalytic activity of miRNA Argonautes across the metazoan phylogeny.

molecular biology↗

bioRxiv2018

MicroRNAs modulate alternative splicing in the C. elegans intestine and body muscle tissues

MicroRNAs (miRNAs) are known to modulate gene expression, but their activity at the tissue-specific level remains largely uncharacterized. In order to study their contribution to tissue-specific gene expression, we developed novel tools to profile miRNA targets in the C. elegans intestine and body muscle. We validated many previously described interactions, and identified ~3,500 novel targets. Many of the miRNA targets curated are known to modulate the functions of their respective tissues. Within our datasets we observed a disparity in the use of miRNA-based gene regulation between the intestine and body muscle. The intestine contained significantly more miRNA targets than the body muscle highlighting its transcriptional complexity. We detected an unexpected enrichment of RNA binding proteins targeted by miRNA in both tissues, with a notable abundance of RNA splicing factors. We developed in vivo genetic tools to validate and further study three RNA splicing factors identified as miRNA targets in our study (asd-2, hrp-2 and smu-2), and show that these factors indeed contain functional miRNA regulatory elements in their 3UTRs that are able to repress their expression in the intestine. In addition, the alternative splicing pattern of their respective downstream targets (unc-60, unc-52, lin-10 and ret-1) is dysregulated when the miRNA pathway is disrupted. A re-annotation of the transcriptome data in C. elegans strains that are deficient in the miRNA pathway from past studies supports and expands on our results. This study highlights an unexpected role for miRNAs in modulating tissue-specific gene isoforms, where post-transcriptional regulation of RNA splicing factors associates with tissue-specific alternative splicing.

molecular biology↗