Genetic and biochemical dissection of mammalian pachytene piRNA biogenesis.

PROJECT SUMMARY Pachytene piRNAs are a population of PIWI-interacting RNAs unique to mammals that are highly expressed in meiotic germ cells. Disruption in pachytene piRNA production results in spermatogenic failure and infertility in both mice and humans. Pachytene piRNAs are generated from long piRNA precursors through cleavage by a piRNA processing machinery near the mitochondrial surface and loaded onto PIWI proteins. Our recent published data revealed the importance of piRNA biogenesis factors and mitochondrial surface-based processing machinery in controlling pachytene piRNA maturation to promote spermatogenesis. However, the molecular mechanism by which pachytene piRNAs are produced and their precise functions remain elusive. In this proposal, we will combine mouse genetics and biochemistry to tackle three key questions that are fundamental to understanding pachytene piRNA biogenesis and function in germ cells: 1) How do regulatory motifs direct PIWI proteins to engage in piRNA biogenesis to promote spermatogenesis? 2) How does the mitochondrial membrane-based piRNA processing machinery dynamically operate? 3) How do mature PIWI/piRNAs exit the processing machinery for effector function? These studies will provide novel insight into the organizing principle of the piRNA pathway and reveal new mechanisms underlying mammalian pachytene piRNA biology important to normal germ cell development, human fertility, and reproductive health.