Characterization and importance of microRNAs in mammalian gonadal functions

Abstract

Recent progress in high throughput sequencing and bioinformatic analysis and other biochemical methods have fuelled our appreciation for the important role of microRNAs (miRNAs) in disease, fertility and development. These tiny RNAs were found to be potentially involved in various aspects of cellular processes of reproductive tissues by posttranscriptional regulation of protein coding genes. Mammalian gonads which exhibit strictly regulated spatiotemporal gene expression patterns are also known to express unique sets of miRNAs and genes involved in the miRNA biogenetic pathway. Studies on miRNAs and their associated processing enzymes have evidenced the contribution of these small regulatory RNAs to germ cell differentiation, post-meiotic male germ cell function and growth, and development and maturation of oocytes through pertaining tightly regulated gene expression. The existence, preferential and temporal expression of miRNAs and their processing machinery genes in different stages of testicular and ovarian cellular development have evidenced the potential role of miRNAs in testicular and ovarian physiology. MiRNAs are also found to be associated with functional regulation of gonadal somatic cells, namely Leydig cells and Sertoli cells in testis and granulosa cells/cumulus cells in the ovary in steroid synthesis. Here, we review the recent works on the involvement and diverse roles of miRNAs in the development and physiology of gonadal cells in mammalian reproduction.

Characterization and expression analysis of microRNAs in Qira black sheep and Hetian sheep ovaries using Solexa sequencing

“…), and miR-99a (EDF1, IGFBP2, etc.) were predicted in this study, and these have already been validated and reported as ovarian function-related genes (Hossain et al, 2009;Hossain et al, 2012b;Yan et al, 2012). One previous study has demonstrated that miR-125b, miR-145, and miR-99a were expressed at significantly higher levels in the ovaries of pregnant goats compared to non-pregnant goats (Zhang et al, 2013).…”

“…Nevertheless, these data add new information to existing data on sheep miRNAs. Similarly, genome-wide miRNA expression profiles have also been examined in whole ovaries from mice (Ro et al, 2007;Mishima et al, 2008), cattle (Hossain et al, 2009;Tripurani et al, 2010;Huang et al, 2011), pig , goat (Zhang et al, 2013), and fetal sheep (Torley et al, 2011); however comparisons across different follicular stages, different stages of the estrous cycle or different breeds were not performed (Hossain et al, 2012b;McBride et al, 2012). Recent studies have also proposed roles for miRNAs in the regulation of follicular development and apoptosis (Baley and Li, 2012;Donadeu et al, 2012).…”

“…These discrepancies will need to be resolved, although they may reflect genuine species differences. Furthermore, in addition to identification and differential expression studies, functional characterization of these miRNAs in sheep follicular development and ovulation, hormone secretion, specific cell lines of ovary at different follicular stages or at different stages of the estrous cycle remain to be explored further (Hossain et al, 2012b), which will further the understanding of the relationship between miRNAs and mammalian reproduction.…”

“…A broad range of biological processes, such as cell differentiation, proliferation and apoptosis, tissue morphogenesis, fertility, metabolism, and immune response, have been shown to be regulated by miRNAs (Ambros, 2004;Plasterk, 2006;Shivdasani, 2006;Sun et al, 2012;Hossain et al, 2012a). As a major regulator of gene expression, several studies have used Solexa sequencing to demonstrate that miRNAs play specific roles in ovarian function and ovulation (Baley and Li, 2012;Hossain et al, 2012b). For example, several studies have been undertaken to identify the distinct miRNAs in the ovaries of pregnant and non-pregnant goats (Zhang et al, 2013), 2-week-old and adult mouse ovaries (Ro et al, 2007), adult bovine ovaries (Hossain et al, 2009), bovine fetal ovaries (Tripurani et al, 2010), and new-born mouse ovaries (Ahn et al, 2010).…”

MicroRNA Regulation of Endocrine Functions in the Ovary

“…In this review we will focus on miRNA's role in regulation of ovarian endocrine function. Important aspects of miRNA regulation not directly related to ovarian endocrine function have been previously reviewed (Christenson 2010 ;Imbar and Eisenberg 2014 ;Donadeu et al 2012 ;Hossain et al 2012 ;Nothnick 2012 ;McGinnis et al 2015 ), so they will not be repeated in-depth in the present review.…”