MOV10L1, a germ cell-specific RNA helicase, is crucial for Piwi-interacting RNAs (piRNAs) biogenesis. PiRNAs are non-coding small RNAs that maintain genome integrity by silencing retrotransposons in germline cells. MOV10L1 is involved in both primary piRNA processing and the 'ping-pong' cycle during secondary piRNA processing [1].

In Mov10l1 knockout (KO) mouse models, primary spermatocytes show activation of LTR and LINE-1 retrotransposons, followed by cell death, leading to male infertility and a complete block of spermatogenesis at early prophase of meiosis I [2]. The genetic disruption of the MOV10L1 RNA helicase domain in mice renders MILI and MIWI2 devoid of piRNAs, causing loss of DNA methylation and subsequent derepression of retrotransposons in germ cells [4]. A point mutation that abolishes the 5'-to-3' RNA-unwinding activity of MOV10L1 in vivo causes a failure in primary piRNA biogenesis [5]. The yama mutation in the MOV10L1 N-terminal region, which results in a single amino acid substitution V229E, causes meiotic arrest, de-repression of transposable elements, and male sterility due to defects in pre-pachytene piRNA biogenesis [3].

In conclusion, MOV10L1 is essential for male fertility as it plays a key role in piRNA-directed retrotransposon silencing in male germ cells. The study of Mov10l1 KO mouse models has provided insights into the mechanism of spermatogenesis and the role of piRNAs in maintaining genome integrity in male germ cells [2,3,4,5].