Hamster PIWI proteins bind to piRNAs with stage-specific size variations during oocyte maturation

Kyoko Ishino,Atsushi Toyoda,Takamasa Hirano,Hinako Ishizaki,Tae Kuramoto,Mikiko C Siomi,Hidetoshi Hasuwa,Naomi M Seki,Haruhiko Siomi,Shinichi Morishita,Jun Yoshimura,Takehiko Itoh,Kuniaki Saito,Marie Tsuchiya,Harumi Masuda,Yuka W Iwasaki,Yasubumi Sakakibara,Hidenori Nishihara

doi:10.1093/nar/gkab059

Abstract

In animal gonads, transposable elements are actively repressed to preserve genome integrity through the PIWI-interacting RNA (piRNA) pathway. In mice, piRNAs are abundantly expressed in male germ cells, and form effector complexes with three distinct PIWIs. The depletion of individual Piwi genes causes male-specific sterility with no discernible phenotype in female mice. Unlike mice, most other mammals have four PIWI genes, some of which are expressed in the ovary. Here, purification of PIWI complexes from oocytes of the golden hamster revealed that the size of the PIWIL1-associated piRNAs changed during oocyte maturation. In contrast, PIWIL3, an ovary-specific PIWI in most mammals, associates with short piRNAs only in metaphase II oocytes, which coincides with intense phosphorylation of the protein. An improved high-quality genome assembly and annotation revealed that PIWIL1- and PIWIL3-associated piRNAs appear to share the 5′-ends of common piRNA precursors and are mostly derived from unannotated sequences with a diminished contribution from TE-derived sequences, most of which correspond to endogenous retroviruses. Our findings show the complex and dynamic nature of biogenesis of piRNAs in hamster oocytes, and together with the new genome sequence generated, serve as the foundation for developing useful models to study the piRNA pathway in mammalian oocytes.

Highlights

Transposition of mobile DNA elements can cause severe damage by disrupting either the structural or regulatory regions on the host genome [1,2,3]
PIWIL1-associated short PIWI-interacting RNA (piRNA) may not be the processed products of loaded long piRNAs, but they may be produced by a mechanism similar to that produced by long piRNAs and loaded onto either newly produced PIWIL1 or PIWIL1, which has unloaded piRNAs
Because it is thought that the size of small guide RNAs is determined by the footprint of small RNA-binding Argonaute/PIWI proteins [28], the change in the size of PIWIL1-associated piRNAs implies a change in the structure of the protein that accommodates short piRNAs

Summary

Introduction

Transposition of mobile DNA elements can cause severe damage by disrupting either the structural or regulatory regions on the host genome [1,2,3]. To avoid such detrimental effects, many animals have a conserved adaptive immune system known as the piRNA pathway in gonads [4,5].

Methods

Results

Conclusion