Target RNA repertoire of mouse Mili and Miwi proteins reveals piRNA biogenesis and Miwi function in spermiogenesis [HITS-CLIP]. Mus musculus

Germ cells employ elaborate mechanisms to maintain and protect their genetic material, and also to regulate gene expression during the complex differentiation process of gametogenesis. Piwi proteins, a subclade of the Argonaute family, are expressed mainly in the germline and bind piRNAs, a novel and diverse class of small RNAs whose biogenesis and putative functions are still largely elusive. We employed High Throughput Sequencing after Crosslinking and Immunoprecipitation (HITS-CLIP) coupled with RNA-Seq to characterize the genome-wide target RNA repertoire of Mili and Miwi, two mouse Piwi proteins. Our analysis outlines a model for primary piRNA biogenesis in postnatal mouse and indicates that piRNAs do not mediate target RNA recognition, but rather are the end products of RNA processing. Moreover, we identify a set of mRNAs essential for spermiogenesis that are bound and regulated by Miwi, directly implicating Piwi proteins in the control of gene expression at key time points of spermiogenesis. Overall design: HITS-CLIP (High Throughput Sequencing after Crosslinking and Immunoprecipitation) experiments targeting two mouse Piwi proteins Mili and Miwi.