Simultaneous existence of a novel microRNA and its precursor in human cells: a novel concept in RNA biology

MicroRNAs (miRNAs) are small noncoding RNAs with ~21 nucleotides (nt) in length, produced via processing of a hairpin-shaped precursor (~70 nt) named pre-miRNA. It is believed that pre-miRNAs become to be immediately processed into mature forms as being functional in their regulatory processes. Additionally, studies have shown that most pre-miRNAs appear to be undetectable due to their short half-lives.In this study, we identified a novel human miRNA (named miR-ex1) that is originated from the 1st exon of OCC-1 gene. In addition to its PCR-amplification, cloning and sequencing, the sequence identity of this miRNA together with its precursor was verified using miRNA-seq data from the NCBI-SRA. RT-PCR method indicated simultaneous expression of miR-ex1 and its precursor in five of eleven tested human cell lines. Furthermore, quantitative analysis of their expression revealed a high expression level of miR-ex1 in the cells with no or undetectable pre-miR-ex1, suggesting a complete processing of it. In contrast, the highest expression level of pre-miR-ex1 was observed in MCF-7 cell line that did not express the mature form, suggesting a complete maintenance of the pre-miR-ex1 in this cell line. Accordingly, a significant correlation (R2= -0.52; p <0.05) was observed between transcription level of miR-ex1 and its precursor across the studied cell lines.Taken together, simultaneous existence of miR-ex1 and its precursor highlights the functionality of pre-miRNAs in human physiology and may open a new avenues of research in the world of tiny RNAs.

Keywords:

MicroRNA , OCC-1 , miRNA-seq , miRNA processing , pre-miRNA stability