microRNAs in the testis: building up male fertility.

Spermatogenesis is a strictly regulated process, at both the transcriptional and the posttranscriptional level, which allows continuous gamete production throughout adulthood. A novel mechanism of posttranscriptional control mediated by microRNAs (miRNAs) has lately emerged as an important regulator of spermatogenesis. miRNAs are endogenous, small, noncoding RNAs produced through a multistep enzymatic process, which involves the action of Dicer, an RNaseIII endonuclease. Here, we first present a short overview of classic posttranscriptional control during spermatogenesis, and then concentrate on recent findings that have unraveled the important role of miRNAs in male reproductive function. Particular focus is given to the in vivo role of miRNAs that has been demonstrated through the generation of Sertoli cell-specific or germ cell-specific Dicer knockouts, as well as the potential application of these findings in the treatment of human male infertility and the development of male contraceptives. It is anticipated that unraveling miRNA functions in the testis will further our understanding of the regulatory mechanisms of mammalian spermatogenesis.