'Inc-miRs': functional intron-interrupted miRNA genes.

The discovery of microRNAs (miRNAs) lin-4 and let-7 as temporal regulators in Caenorhabditis elegans led to broader searches for novel miRNAs and their biological roles. Unlike protein-coding genes and some long noncoding RNAs, canonical metazoan miRNAs are not known to contain introns within their genomic precursor sequences. Because the short length of miRNAs complicates a statistically definitive assignment of split genes in RNA sequencing data sets, we took an experimental approach toward testing the compatibility of splicing and functional miRNA biogenesis. To definitively evaluate the possibility that miRNAs could derive from interrupted genes, we constructed intron-interrupted variants of C. elegans lin-4 and assayed for their miRNA-encoding capability and biological activity in the developing organism. Our studies indicate that (1) intron-containing miRNAs (inc-miRs) can be efficiently spliced and processed to produce miRNAs with normal termini, and (2) these miRNAs can be functional in full rescue of developmental phenotypes in null mutants lacking endogenous lin-4. This study provides the first evidence to support the ability of intron-interrupted miRNA precursors to produce functional regulators and identifies an additional modality available for metazoan miRNA production.