[A novel class of testis-specific small RNAs: piRNAs]

Eukaryotes produce various types of 19-30 nt small RNAs, which act as guides to the regulation of gene expressions, such as mRNA degradation and translational repression. The Argonaute family members related to small RNA functions fall into 2 subfamilies. One is the AGO subfamily, whose 4 members distribute widely, confirmedly bind to miRNAs and siRNAs and inhibit the expression of target mRNAs through a pathway like RNA interference. The other is the PIWI subfamily, including PIWI, Aubgine (AUB) and AGO3, exclusively expressed in the testis. Recently, four research groups have isolated a new class of small RNAs from the mammalian testis, which interacts with the PIWI subfamily, hence named piwi-interfering RNAs (piRNAs), and is suggestive of an important role in spermatogenesis.