Identification and characterization of a novel non-coding RNA involved in sperm maturation

A long and ever-expanding roster of small (∼20-30 nucleotides) RNAs has emerged during the last decade, and most can be subsumed under the three main headings of microRNAs (miRNAs), Piwi-interacting RNAs (piRNAs), and short interfering RNAs (siRNAs). Among the three categories, miRNAs is the most quickly expanded group. The most recent number of identified miRNAs is 16,772 (Sanger miRbase, April 2011). However, there are insufficient publications on their primary forms, and no tissue-specific small RNAs precursors have been reported in the epididymis. Here, we report the identification in rats of an epididymis-specific, chimeric, noncoding RNA that is spliced from two different chromosomes (chromosomes 5 and 19), which we named HongrES2. HongrES2 is a 1.6 kb mRNA-like precursor that gives rise to a new microRNA-like small RNA (mil-HongrES2) in rat epididymis. The generation of mil-HongrES2 is stimulated during epididymitis. An epididymis-specific carboxylesterase named CES7 had 100% cDNA sequence homology at the 3'end with HongrES2 and its protein product could be downregulated by HongrES2 via mil-HongrES2. This was confirmed in vivo by initiating mil-HongrES2 over-expression in rats and observing an effect on sperm capacitation.