PIWI/piRNA machinery in spermatogenesis

PIWI proteins are specifically expressed in animal germ cells, and have been well demonstrated to be essential for germline development and gametogenesis. Recently, PIWI-interacting RNAs (piRNAs), a novel class of germ-cell-specific small noncoding RNAs, have been found associated with PIWI proteins. PIWI/piRNA machinery silence transposable elements and regulate the expression levels of mRNAs duringgermline development and gametogenesis. In this review, we summarize the recent progress of the functions and mechanisms of PIWI/piRNA machinery.