Identification of piRNAs and piRNA clusters in the testes of the Mongolian horse

Bei Li,Shaofeng Su,Gerelchimeg Bou,Rui Liu,Dugarjaviin Manglai,Dongyi Bai,Xinzhuang Zhang,Yiping Zhao,Yuejiao Wang,Leng Dao,Xiaolong He

doi:10.1038/s41598-019-41475-9

Abstract

P-element induced wimpy testis-interacting RNAs (piRNAs) are essential for testicular development and spermatogenesis in mammals. Comparative analyses of the molecular mechanisms of spermatogenesis among different organisms are therefore dependent on accurate characterizations of piRNAs. At present, little is known of piRNAs in non-model organisms. Here, we characterize piRNAs in the Mongolian horse, a hardy breed that reproduces under extreme circumstances. A thorough understanding of spermatogenesis and reproduction in this breed may provide insights for the improvement of fecundity and reproductive success in other breeds. We identified 4,936,717 piRNAs and 7,890 piRNA clusters across both testicular developmental stages. Of these, 2,236,377 putative piRNAs were expressed in the mature samples only, and 2,391,271 putative piRNAs were expressed in the immature samples only. Approximately 3,016 piRNA clusters were upregulated in the mature testes as compared to the immature testes, and 4,874 piRNA clusters were downregulated. Functional and pathway analyses indicated that the candidate generating genes of the predicted piRNAs were likely involved in testicular development and spermatogenesis. Our results thus provide information about differential expression patterns in genes associated with testicular development and spermatogenesis in a non-model animal.

Highlights

Cloning of miRNAs in mouse testis identified 381(~27 nt) putative P-element induced wimpy testis-interacting RNAs (piRNAs), while only 40 putative miRNAs(~22 nt) were identified in mouse oocytes, suggesting that piRNAs may have a specific role in the germlines of male mammals[7,8]
Consistent with previous results, the piRNAs that we identified in the Mongolian horse had a bias for U at the 5′ end, and in some cases the 10th base had a bias for A32; these bases are characteristic of miRNA sequences[32,33]
It is possible that these sequence features might be related to the ping-pong model of piRNA generation[33]

Summary

Introduction

Cloning of miRNAs in mouse testis identified 381(~27 nt) putative piRNAs, while only 40 putative miRNAs(~22 nt) were identified in mouse oocytes, suggesting that piRNAs may have a specific role in the germlines of male mammals[7,8]. In the germ cells of male mice, pre-pachytene piRNAs interact with the PIWI proteins MIWI2 and MILI111–14 These proteins, in combination with transposons, retrotransposons, and other mobile genetic elements, ensure the normal development and differentiation of spermatogenic cells by inhibiting the activity of transposable elements at the epigenetic and post-transcriptional levels[15]. We selected the Mongolian horse for piRNA characterization, as this breed is ancient, possibly expressing a phenotype ancestral to other Chinese, Japanese, and even Northern European horse breeds[17,18,19]. This breed has high endurance and is unusually hardy compared to other horses. In this study we aimed to characterize the piRNAs from the testes of the Mongolian horse

Objectives

Methods

Conclusion