piRNA and PIWI in animal germ cells

A novel class of small non-coding RNA termed as PIWI-interacting RNA (piRNA) was recently discovered in the mammalian and Drosophila germline. Through interacting with PIWI family of proteins,the 26-32 nt long piRNA may represent a distinct small RNA pathway that contributes to transposon silencing in germ cells via novel mechanisms of epigenetic and posttranscriptional regulation. piRNAs and PIWI proteins are predominantly present in the germ cells and crucial to germline stem cell (GSC) self-renewal and differentiation,meiosis,spermiogenesis,and other gametogenic events. Impressive progresses have been achieved in understanding the biogenesis,function and mechanism of piRNA in the past year. A few of the recent progresses were summarized here.