PIWIL3 Forms a Complex with TDRKH in Mammalian Oocytes.

Minjie Tan,Helena T.A Van Tol,Bernard A.J Roelen,David Rosenkranz,Mirjam J Damen,Tom A.E Stout,Wei Wu,Elke F Roovers

doi:10.3390/cells9061356

Minjie Tan, Helena T.A Van Tol + Show 6 more

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https://doi.org/10.3390/cells9061356

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Abstract

P-element induced wimpy testis (PIWIs) are crucial guardians of genome integrity, particularly in germ cells. While mammalian PIWIs have been primarily studied in mouse and rat, a homologue for the human PIWIL3 gene is absent in the Muridae family, and hence the unique function of PIWIL3 in germ cells cannot be effectively modeled by mouse knockouts. Herein, we investigated the expression, distribution, and interaction of PIWIL3 in bovine oocytes. We localized PIWIL3 to mitochondria, and demonstrated that PIWIL3 expression is stringently controlled both spatially and temporally before and after fertilization. Moreover, we identified PIWIL3 in a mitochondrial-recruited three-membered complex with Tudor and KH domain-containing protein (TDRKH) and poly(A)-specific ribonuclease-like domain containing 1 (PNLDC1), and demonstrated by mutagenesis that PIWIL3 N-terminal arginines are required for complex assembly. Finally, we sequenced the piRNAs bound to PIWIL3-TDRKH-PNLDC1 and report here that about 50% of these piRNAs map to transposable elements, recapitulating the important role of PIWIL3 in maintaining genome integrity in mammalian oocytes.

Highlights

Genomic integrity is critical for faithful propagation within the species
PIWIL1, PIWIL2, and PIWIL4 have been elucidated in mouse testis [10,26] and human fetal oocytes [14], the subcellular compartment(s) in which PIWIL3 exerts its function remains uninvestigated to date
As a PIWIL3 ortholog is absent from the mouse genome, the function of PIWIL3 has not been studied by gene knockout and has remained largely unknown

Summary

Introduction

Ensuring genome integrity entails controlling transposable elements (TEs), which are mobile DNA sequences that can migrate within the genome [1]. Among various TEs, retrotransposons are especially damaging as these can be transcribed, reverse transcribed, and reinserted at multiple locations in the genome. While retrotransposon activity may be minimized by repressive DNA (cytosine)methylation, germ cells and early embryos are vulnerable to retrotransposon reinsertion because, in these developmental stages, cells undergo genome-wide demethylation [2]. Maintenance of genome integrity in oocytes and early developing embryos against TEs is extremely important, as any genetic change would be passed on to the generation. P-element induced wimpy testis (PIWI) proteins, belonging to the Argonaute protein subfamily, form specific RNA-induced silencing complexes that, by interacting with 21–31 nucleotides non-coding PIWI interacting (pi)RNAs, form an efficient system to silence TE activity

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