中文摘要：

miRNA系统在高等多细胞真核生物中得到了广泛深入的研究。近年来，人们在单细胞真核生物上的miRNA研究也取得了重要进展。这不仅丰富了人们对miRNA在整个生物界中的认识，更重要的是对于揭示miRNA这一表达调节系统是如何在生物界中起源进化的问题具有重要意义。该文结合作者在最低等单细胞真核生物——贾第虫上的研究结果，对该领域的研究进展作一概述，并对有关miRNA这一系统的起源进化问题进行了探讨。

英文摘要：

microRNAs （miRNAs） in higher multicellular eukaryotes have been extensively studied in recent years. Great progresses have also been achieved for miRNAs in unicellular eukaryotes. All these studies not only enrich our knowledge about the complex expression regulation system in diverse organisms, but also have evolutionary significance for understanding the origin of this system. In this review, Authors summarize the recent advance in the studies of miRNA in unicellular eukaryotes, including that on the most primitive unicellular eukaryote--Giardia. The origin and evolution of miRNA system is also discussed.