中文摘要：

CpG二核苷酸中胞嘧啶的甲基化形式5-甲基胞嘧啶（5-methylcytosine,5mC）在哺乳动物中是一种常见的表观遗传修饰,在基因表达调控、发育调节、基因组印迹等方面发挥重要作用。近3年来研究发现,除了5mC外,胞嘧啶碱基的另一种修饰—5-羟甲基胞嘧啶（5-hydroxymethylcytosine,5hmC）在哺乳动物的多种组织中有着丰富的表达,它可能与5mC有着不同的生物学功能。文章就近年来5hmC的研究进展进行了综述。

英文摘要：

5-methylcytosine（5mC） in cytosine-guanine dinucleotide（CpG） is a usual epigenetic modification in mammals.It plays crucial roles in gene regulation,development,genomic imprinting and so on.In the last three years,it was discovered that in addition to 5mC,another modified cytosine base—5-hydroxymethylcytosine（5hmC） was abundant in many mammalian tissues,which may have different biological function from 5mC.This paper reviews the recent progresses in the studies of 5hmC.