Mitochondrial membrane-based initial separation of MIWI and MILI functions during pachytene piRNA biogenesis.

Deqiang Ding,Chen Chen,Jiali Liu,Kunzhe Dong,Ashley F Melnick,Keith E Latham

doi:10.1093/nar/gky1281

Abstract

PIWI-interacting RNAs (piRNAs) engage PIWI proteins to silence transposons and promote germ cell development in animals. In diverse species, piRNA biogenesis occurs near the mitochondrial surface, and involves mitochondrial membrane-anchored factors. In mice, two cytoplasmic PIWI proteins, MIWI and MILI, receive processed pachytene piRNAs at intermitochodrial cement (IMC). However, how MIWI and MILI are initially recruited to the IMC to engage multiple steps of piRNA processing is unclear. Here, we show that mitochondria-anchored TDRKH controls multiple steps of pachytene piRNA biogenesis in mice. TDRKH specifically recruits MIWI, but not MILI, to engage the piRNA pathway. It is required for the production of the entire MIWI-bound piRNA population and enables trimming of MILI-bound piRNAs. The failure to recruit MIWI to the IMC with TDRKH deficiency results in loss of MIWI in the chromatoid body, leading to spermiogenic arrest and piRNA-independent retrotransposon LINE1 de-repression in round spermatids. Our findings identify a mitochondrial surface-based scaffolding mechanism separating the entry and actions of two critical PIWI proteins in the same piRNA pathway to drive piRNA biogenesis and germ cell development.

Highlights

P-element induced wimpy testis (PIWI)-interacting RNAs are a major class of small regulatory RNAs that plays evolutionarily conserved roles in the animal germline to suppress harmful transposons and promote germ cell development [1,2,3,4,5,6,7]
Conditional deletion of Tdrkh in postnatal germ cells leads to spermiogenic arrest To define the specific involvement of TDRKH in PIWI regulation and pachytene PIWI-interacting RNAs (piRNAs) biogenesis in postnatal germ cells, we generated Tdrkh conditional knockout (TdrkhcKO) mice in which Tdrkh was deleted in prospermatogonia starting at postnatal Day 3 by Stra8-Cre transgene [29,39]
We demonstrate that TDRKH acts as a key mitochondria-anchored scaffold protein that recruits MIWI to the intermitochodrial cement (IMC) and tethers PNLDC1 to couple two key piRNA biogenesis steps during pachytene piRNA biogenesis: MIWI recruitment and piRNA trimming

Summary

Introduction

P-element induced wimpy testis (PIWI)-interacting RNAs (piRNAs) are a major class of small regulatory RNAs that plays evolutionarily conserved roles in the animal germline to suppress harmful transposons and promote germ cell development [1,2,3,4,5,6,7]. Different PIWI orthologs associate with distinct piRNA populations during different stages of germ cell development to fulfill specific functions. Three PIWI proteins (MIWI, MILI and MIWI2) associate with two distinct developmental stage-specific piRNA populations [13]. In fetal/neonatal germ cells, MILI and MIWI2 associate with transposon sequence-rich fetal piRNAs to suppress transposable elements and maintain germline genome integrity [11,12,14]. MIWI and MILI associate instead with transposon sequence-poor pachytene piRNAs that are expressed beginning in the pachytene stage of meiosis to regulate meiotic and postmeiotic gene expression [15,16,17]. Pachytene piRNAs are unique to mammals and are crucial for adult spermatogenesis in mice

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