Specifically required during spermatogenesis to promote expression of piRNA precursors. The piRNA metabolic process mediates the repression of transposable elements during meiosis by forming complexes composed of piRNAs and Piwi proteins and governs the methylation and subsequent repression of transposons, which is essential for the germline integrity. Acts by facilitating transcription elongation at piRNA loci during pachytene. Expressed in testis. Expressed during pachytene in testis: accumulates in early pachytene cells (stages I-VII), declines in late pachytene cells (stages VIII-X) and disappears in diplotene cells (stage XI) (at protein level). Expressed from spermatogonia to spermatids, with trace expression in mature spermatozoa and somatic Sertoli cells. Mice are viable but show male sterility due to defects in spermatogenesis. Retrotransposons are derepressed due to DNA demethylation. Defects are caused by impaired piRNA biogenesis.