miRNA异构体：miRNA序列多样性

微RNA（microRNA，miRNA)是一类抑制基因表达的调控分子，在多种生物学进程中扮演重要角色。近来，基于新一代测序技术获得的小RNA测序数据发现，对于某一miRNA来说，它并不是单一的序列，而是由一系列长度/序列及表达不同的异构微RNA (isomicroRNA, isomiRNA/isomiR)所组成。这些isomiR表达多样且序列多样，甚至引入多样的5′端及种子区域。特定miRNA位点在疾病组织中可具有异常的表达模式，现已证实，部分isomiR具有重要的生物学功能。所关注的经典miRNA序列，其实仅是多重isomiR序列中的1条特殊序列，仅从miRNA角度的研究已不足以揭示小RNA的奥秘，全面的研究应同时在miRNA和isomiR中开展，由此可进一步拓宽miRNA的研究思路。本文主要从isomiR的生物学特点、表达及功能等方面进行介绍。

Isoforms of MiRNA: MiRNA Sequence Diversity

MicroRNA (miRNA) is a class of regulatory molecule and has critical roles in multiple biological progresses by repressing gene expression. Recently, in-depth analysis based on small RNA sequencing data suggests that miRNA is not a single sequence, but is composed of a series of miRNA isoforms (isomicroRNA, isomiRNA/isomiR) with various lengths/sequences and expression levels. These isomiRs have diverse expression levels and sequences, and even some of them are involved in diverse 5' terminus and seed regions. Specific miRNA locus may generate abnormal expression pattern in disease, and some isomiRs have been identified with important biological function. The canonical miRNA sequence is only one specific sequence in multiple isomiRs, and study of miRNA is not enough to reveal the secrets of the small RNA world. A comprehensive study should be performed from miRNA and isomiR levels, which can broaden the miRNA study. Herein, we mainly summarized biological characteristics, expression and function of isomiR.