Cloning and identification of novel microRNAs from rat hippocampus.

MicroRNAs (miRNAs) are small regulatory molecules post-transcriptionally suppressing mRNA activity. Many miRNAs in various organisms have been cloned but many unknown miRNAs remain to be identified. Here we describe the cloning of six new miRNAs from rat hippocampus. Among them, four were not found in the rat miRBase, but were identical to their human and/or mouse homolog, therefore they were designated as rno-miR-92b, rno-miR-146b, rno-let-7g, and rno-miR-551b. The other two were derived from the other arms of the known miRNA precursors of rno-miR-330 and rno-miR-384, and were not found in miRBase of all organisms. They were designated as rno-miR-330* and rno-miR-384*. The expression of these miRNAs was confirmed by RNA-tailing and primer-extension real-time reverse transcription-polymerase chain reaction. These six miRNAs were expressed at significantly higher levels in the hippocampus than in other tissues, including cerebral cortex, heart, liver, lung and kidney. miR-384* was 10 times more abundant than miR-384 in rat hippocampus, but little difference was found between miR-330* and miR-330 expression in the same tissue.