Functional and structural insights into the piRNA factor Maelstrom.

PIWI-interacting RNA (piRNA) is a germline-specific class of small non-coding RNAs that repress transposons in the gonads. Mael, which comprises a high mobility group box and a MAEL domain, is one of the key players in piRNA-mediated transposon silencing. However, the mechanism whereby Mael is involved in this pathway remains unknown. Recent biochemical and structural studies, along with bioinformatic analyses of Mael-associating RNAs in vivo, have shed light on the functional aspects of Mael in the piRNA pathway. We summarize the current understanding of Mael functions in the piRNA pathway, particularly in Drosophila and in mice.