The genetic codes inscribed during two key developmental processes, namely gametogenesis and embryogenesis, are believed to determine subsequent development and survival of adult life. Once the embryo is formed, its further development mainly depends on its intrinsic characteristics, maternal environment (the endometrial receptivity), and the embryo–maternal interactions established during each phase of development. These developmental processes are under strict genetic regulation that could be manifested temporally and spatially depending on the physiological and developmental status of the cell. MicroRNAs (miRNAs), one of the small non-coding classes of RNAs, approximately 19–22 nucleotides in length, are one of the candidates for post-transcriptional developmental regulators. These tiny non-coding RNAs are expressed in ovarian tissue, granulosa cells, testis, oocytes, follicular fluid, and embryos and are implicated in diverse biological processes such as cell-to-cell communication. Moreover, accumulated evidences have also highlighted that miRNAs can be released into the extracellular environment through different mechanisms facilitating intercellular communication. Therefore, understanding miRNAs mediated regulatory mechanisms during gametogenesis and embryogenesis provides further insights about the molecular mechanisms underlying oocyte/sperm formation, early embryo development, and implantation. Thus, this review highlights the role of miRNAs in mammalian gametogenesis and embryogenesis and summarizes recent findings about miRNA-mediated post-transcriptional regulatory mechanisms occurring during early mammalian development.

The Role of MicroRNAs in Mammalian Fertility: From Gametogenesis to Embryo Implantation

A cross-species comparative approach to assessing multi- and transgenerational effects of endocrine disrupting chemicals.

Long non-coding RNAs (lncRNAs) have been found to participate in the regulation of human spermatogenic cell development. However, little is known about the abnormal expression of lncRNAs associated with spermatogenic failure and their molecular mechanisms. Using lncRNA microarray of testicular tissue for male infertility and bioinformatics methods, we identified the relatively conserved lncRNA Gm2044 which may play important roles in non-obstructive azoospermia. The UCSC Genome Browser showed that lncRNA Gm2044 is the miR-202 host gene. This study revealed that lncRNA Gm2044 and miR-202 were significantly increased in non-obstructive azoospermia of spermatogonial arrest. The mRNA and protein levels of Rbfox2, a known direct target gene of miR-202, were regulated by lncRNA Gm2044. Furthermore, the miR-202-Rbfox2 signalling pathway was shown to mediate the suppressive effects of lncRNA Gm2044 on the proliferation of human testicular embryonic carcinoma cells. Understanding of the molecular signalling pathways for lncRNA-regulated spermatogenesis will provide new clues into the pathogenesis and treatment of patients with male infertility.

https://www.tandfonline.com/doi/pdf/10.1080/19768354.2019.1591506

Upregulated lncRNA Gm2044 inhibits male germ cell development by acting as miR-202 host gene.

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression primarily at the post-transcriptional levels and thereby play important roles in regulating many physiological and developmental processes Oocyte maturation in fish is induced by hormones produced from the hypothalamus, pituitary, and ovary Gonadotropin-releasing hormone (GnRH) stimulates the secretion of luteinizing hormone (LH), which in turn, induces the secretion of maturation-inducing hormone (MIH) from the ovary It is documented that small early vitellogenic (or stage IIIa) follicles are unable to undergo oocyte maturation whereas oocytes in mid- to late vitellogenic (stage IIIb) follicles can be induced by LH and MIH to become mature To determine whether miRNAs may be involved in the growth and acquisition of maturational competency of ovarian follicles, we determined the miRNA expression profiles in follicular cells collected from stage IIIa and IIIb follicles using next-generation sequencing It was found that miRNAs are abundantly expressed in the follicular cells from both stages IIIa and IIIb follicles Furthermore, bioinformatics analysis revealed the presence of 214 known, 31 conserved novel and 44 novel miRNAs in zebrafish vitellogenic ovarian follicular cells Most mature miRNAs in follicular cells were found to be in the length of 22 nucleotides Differential expression analysis revealed that 11 miRNAs were significantly up-regulated, and 13 miRNAs were significantly down-regulated in the stage IIIb follicular cells as compared with stage IIIa follicular cells The expression of four of the significantly regulated miRNAs, dre-miR-22a-3p, dre-miR-16a, dre-miR-181a-3p, and dre-miR-29a, was validated by real-time PCR Finally, gene enrichment and pathway analyses of the predicted targets of the significantly regulated miRNAs supported the involvement of several key signaling pathways in regulating ovarian function, including oocyte maturation Taken together, this study identifies novel zebrafish miRNAs and characterizes miRNA expression profiles in somatic cells within the zebrafish ovarian follicles The differential expression of miRNAs between stage IIIa and IIIb follicular cells suggests that these miRNAs are important regulators of zebrafish ovarian follicle development and/or oocyte maturation

/pdf/identification-of-novel-micrornas-and-characterization-of-1fg7okm1jj.pdf

Identification of Novel MicroRNAs and Characterization of MicroRNA Expression Profiles in Zebrafish Ovarian Follicular Cells

Thousands of circular RNAs (circRNAs) have been recently discovered in cumulus cells and oocytes from several species. However, the expression and function of circRNA during porcine oocyte meiotic maturation have been never examined. Here, we separately identified 7,067 and 637 circRNAs in both cumulus cells and oocytes via deep sequencing and bioinformatic analysis. Further analysis revealed that a faction of circRNAs is differentially expressed (DE) in a developmental stage-specific manner. The host genes of DE circRNAs are markedly enriched to multiple signaling pathways associated with cumulus cell function and oocyte maturation. Additionally, most DE circRNAs harbor several miRNA targets, suggesting that these DE circRNAs potentially act as miRNA sponge. Importantly, we found that maternal circARMC4 knockdown by siRNA microinjection caused a severely impaired chromosome alignment, and significantly inhibited first polar body extrusion and early embryo development. Taken together, these results demonstrate for the first time that circRNAs are abundantly and dynamically expressed in a developmental stage-specific manner in cumulus cells and oocytes, and maternally expressed circARMC4 is essential for porcine oocyte meiotic maturation and early embryo development.

/pdf/circular-rna-profiling-in-the-oocyte-and-cumulus-cells-250w4vk9ve.pdf

Circular RNA profiling in the oocyte and cumulus cells reveals that circARMC4 is essential for porcine oocyte maturation.

Female gamete production relies on coordinated molecular and cellular processes that occur in the ovary throughout oogenesis In fish, as in other vertebrates, these processes have been extensively studied both in terms of endocrine/paracrine regulation and protein expression and activity The role of small non-coding RNAs in the regulation of animal reproduction remains however largely unknown and poorly investigated, despite a growing interest for the importance of miRNAs in a wide variety of biological processes Here, we analyzed the role of miR-202, a miRNA predominantly expressed in male and female gonads in several vertebrate species We studied its expression in the medaka ovary and generated a mutant line (using CRISPR/Cas9 genome editing) to determine its importance for reproductive success with special interest for egg production Our results show that miR-202-5p is the most abundant mature form of the miRNA and that it is expressed in granulosa cells and in the unfertilized egg The knock out (KO) of mir-202 gene resulted in a strong phenotype both in terms of number and quality of eggs produced Mutant females exhibited either no egg production or produced a dramatically reduced number of eggs that could not be fertilized, ultimately leading to no reproductive success We quantified the size distribution of the oocytes in the ovary of KO females and performed a large-scale transcriptomic analysis approach to identified dysregulated molecular pathways Together, cellular and molecular analyses indicate that the lack of miR-202 impairs the early steps of oogenesis/folliculogenesis and decreases the number of large (ie vitellogenic) follicles, ultimately leading to dramatically reduced female fecundity This study sheds new light on the regulatory mechanisms that control the early steps of follicular development, including possible targets of miR-202-5p, and provides the first in vivo functional evidence that a gonad-predominant microRNA may have a major role in female reproduction

/pdf/mir-202-controls-female-fecundity-by-regulating-medaka-tkcjjipu2n.pdf

MiR-202 controls female fecundity by regulating medaka oogenesis

Female gamete production relies on coordinated molecular and cellular processes that occur in the ovary throughout oogenesis. In fish, as in other vertebrates, these processes have been extensively studied both in terms of endocrine/paracrine regulation and protein expression and activity. The role of small non-coding RNAs in the regulation of animal reproduction remains however largely unknown and poorly investigated, despite a growing interest for the importance of miRNAs in a wide variety of biological processes. Here, we analyzed the role of miR-202, a miRNA predominantly expressed in male and female gonads in several vertebrate species. We studied its expression in the medaka ovary and generated a mutant line (using CRISPR/Cas9 genome engineering) to determine its importance for reproductive success with special interest for egg production. Our results show that miR-202-5p is the biologically active form of the miRNA and that it is expressed in granulosa cells and in the unfertilized egg. The knock out (KO) of miR-202 resulted in a strong phenotype both in terms of number and quality of eggs produced. Mutant females exhibited either no egg production or produced a drastically reduced number of eggs that could not be fertilized, ultimately leading to no reproductive success. We quantified the size distribution of the oocytes in the ovary of KO females and performed a genome-wide transcriptomic analysis approach to identified dysregulated molecular pathways. Together, cellular and molecular analyses indicate that lack of miR-202 impairs the early steps of oogenesis/folliculogenesis and decreases the number of large (i.e. vitellogenic) follicles, ultimately leading to dramatically reduced female fecundity. This study sheds new light on the regulatory mechanisms that control the early steps of follicular development and provides the first in vivo functional evidence that an ovarian-predominant microRNA may have a major role in female reproduction.

https://www.biorxiv.org/content/biorxiv/early/2018/03/22/287359.full.pdf

MicroRNA-202 (miR-202) controls female fecundity by regulating medaka oogenesis

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MiR-202 controls female fecundity by regulating medaka oogenesis

MicroRNA-202 (miR-202) controls female fecundity by regulating medaka oogenesis