A distinct class of small RNAs arises from pre-miRNA-proximal regions in a simple chordate

We report the comprehensive sequencing of small RNA libraries created from different developmental stages of the basal chordate, Ciona intestinalis. Surprisingly, half of the identified miRNA loci encode not two, but up to four distinct small RNAs. These additional RNAs, termed “moRs”, are generated from sequences adjacent to the predicted ~60-nt pre-miRNA. moRs appear to be produced by RNAse-III-like processing, are ~20-nt in length, have 5’-monophosphate and 3’-hydroxl termini, and like miRNAs, are developmentally regulated. Sequencing of small RNA libraries from 4 stages of Ciona intestinalis. Ciona_LarvaMir309_RNASeq and Dmel_Toll10b_RNASeq are sequencing runs to detect if the expression of these RNA products is specific to Ciona or not. An ectopic transcript of the Drosophila melanogaster miR-309 locus was expressed in Ciona to see if it processed the miRs differently than Drosophila melanogaster. The Dmel sequence is from the endogenous case and is a control for comparison.