A chromodomain protein mediates heterochromatin-directed piRNA expression

Significance PIWI-interacting RNAs (piRNAs) are highly conserved among metazoan and act to distinguish self and nonself nucleic acids, silence transposable elements, defend against viral infections, protect germline integrity, and mediate transgenerational inheritance. How piRNA source loci are efficiently transcribed is poorly understood. In this work, we used both forward and reverse genetic approaches to decipher the molecular mechanisms of piRNA transcription in the Caenorhabditis elegans germline. We identified a chromodomain protein, UAD-2, that is required for piRNA focus formation, the association of an upstream sequence transcription complex with the piRNA genes, and piRNA production. This work suggested that transcription of heterochromatic piRNA loci relies on coordinated recruitment of both the readers of histone marks and the core transcriptional machinery.