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

Abstract

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.

Comprehensive transcriptome analysis of hypothalamus reveals genes associated with disorders of sex development in pigs

“…The ErB signaling pathway [65] and the cAMP signaling pathway [66] positively regulates GnRH secretion. Ssc-miR-181a is the hub miRNA in the sub-CeNET, and it is reported that miR-181a was participated the ovarian follicle development [67]. Here ssc-miR-181a was predicted to target PAK6.…”

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

“…Similarly, in zebra fish it is believed that small early vitellogenic follicles are unable to undergo oocyte maturation whereas oocytes in mid-to late vitellogenic follicles can be induced by Luteinizing hormone (LH) to become matured. With this respect, several miRNAs were found to be abundantly expressed in the follicular cells from early vitellogenic and mid-to late vitellogenic stages follicles but the expression patterns of 24 miRNAs including miR-22a-3p, miR-16a, miR-181a-3p, and miR-29a were altered in follicles that were unable to undergo oocyte maturation [34].…”

Role of sex‐biased miRNAs in teleosts – a review

“…When treated with human chorionic gonadotropin (hCG) and forskolin, it significantly repressed the expression of miR-17a and miR-430b in cultured follicular cells, thus depicting a clear role of these miRNAs in facilitating hormonal regulation of gene expression. A recent expression profiling study also identified 24 differentially regulated miRNA transcripts in Type IIIa and IIIb zebrafish follicles that included miR-16a, miR-22a-3p, miR-29a and miR-181a-3p (Zayed et al 2019). This study also found miR-202-5p to be the most abundant transcript in the vitellogenin follicles and suggested its involvement in follicle development and oocyte maturation.…”

“…A recent expression profiling study also identified 24 differentially regulated miRNA transcripts in Type IIIa and IIIb zebrafish follicles that included miR‐16a, miR‐22a‐3p, miR‐29a and miR‐181a‐3p (Zayed et al . 2019). This study also found miR‐202‐5p to be the most abundant transcript in the vitellogenin follicles and suggested its involvement in follicle development and oocyte maturation.…”