Trimming it short: PNLDC1 is required for piRNA maturation during mouse spermatogenesis

Abstract

Transposon silencing within the germ line requires the proper processing of piRNA intermediates. However, the enzyme that is required for piRNA 3′ end maturation in vertebrates remained enigmatic. Nishimura et al 1 in this issue of EMBO Reports and two independent studies 2, 3 now identified PNLDC1 as the exonuclease that is responsible for piRNA 3′ end processing and transposon silencing during mouse spermatogenesis. Together, these studies establish PNLDC1 as the piRNA 3′ end trimmer in mouse.

Figure 1. piRNA biogenesis during mouse spermatogenesis

Zucchini‐driven and slicer‐driven endonuclease activities represent two different modes for piRNA 5′ end generation. This step of piRNA biogenesis may be spatially and/or mechanistically coupled to loading into Piwi proteins (Mili, Miwi, Miwi2). The resulting piRNA intermediates need to be further trimmed at their 3′ end, which requires TdrKH and PNLDC1. The mature piRNA is methylated at its 3′ end by the methyltransferase Hen1. The Miwi2/piRNA complex acts in the nucleus to repress retrotransposon transcription. TGS: transcriptional gene silencing.