Expression analysis of Mirna Isomirs from deep sequencing data

Recently, several researches have reported the novel phenomena of microRNA isoforms (isomiRs), that microRNAs (miRNAs) can exhibit heterogeneous ends in 5´ and 3´ end, both addition and subtractionof diverse oligonucleotide. With the benefit of high-throughput sequencing technology, the expression profiles of miRNAs were analyzed here in the samples of the placentas of pregnant women after their delivery. By analyzing the profiles of miRNAs in four samples, we found three notable results. (1) The phenomenas of isomiRs were ubiquitous in all four samples. (2) The heterogeneous ends in 3´end were more significantly than in 5´ end, but showed no novel difference between the addition and subtraction of nucleotide in the ends. (3) The isomiRs with one and two nucleic acids heterogeneous took up approximately the same percentage with the mature miRNA in miRBase, and those isomiRs with more than 2 nt differences only took small part of the total miRNAs in the profiles. These results indicated the isomiRs maybe not just the inexact Dicer processing, but were the product of pre-miRNAs with some unknown but special bio-rules, which could give some impressing suspects for researches to better understand this novel phenomena ofisomiRs.