Primary piRNA biogenesis: caught up in a Maelstrom

Precursors for most Piwi‐interacting RNAs (piRNAs) are indistinguishable from other RNA polymerase II‐transcribed long non‐coding RNAs. So, it is currently unclear how they are recognized as substrates by the piRNA processing machinery that resides in cytoplasmic granules called nuage. In this issue, Castaneda et al (2014) reveal a role for the nuage component and nucleo‐cytoplasmic shuttling protein Maelstrom in mouse piRNA biogenesis. Graphical Abstract In pachytene spermatids, piRNA biogenesis depends on Maelstrom, a nucleo‐cytoplasmic shuttling protein and component of nuage granules. Generally, mammalian piRNAs target transposable elements, but in the male germline, acrosome and flagella formation are piRNA‐dependent.