Fat deposition [2,32-34], indicating that miR-143 may play an important role
Fat deposition [2,32-34], indicating that miR-143 may play an important role in normal mammalian physical development, as well as mammalian reproduction. It is a challenge to verify the complex functions of miRNAs. In the previous studies, miR-21 exerted an anti-apoptotic effect during the transformation of ovarian granulosa cells into luteal cells, and repression of miR-21 expression induced granulosa cell apoptosis and significantly reduced the rate of ovulation, via a mechanism dependent on luteinizing hormone secretion [35]. Also, miR-21 was demonstrated to express at significantly higher levels in PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/26437915 the ovaries of Holstein cows compared to the testis (1.97-fold), indicating that miR-21 may play an important role in ovarian function [29]. Interestingly, the present study also showed that miR-21 was significantly upregulated in pregnant goat ovaries, compared to non-pregnant goat ovaries (1.92-fold). Increased LH secretion after becoming pregnant, followed by upregulation of miR-21 expression, may contribute to the transformation of ovarian granulosa cells into luteal cells. And the mechanisms regulating the anti-apoptotic effects of miR-21 in ovarian granulosa cells still need to be investigated further [36]. Recent research has indicated that specific members of the let-7 family can affect mammalian reproduction,Zhang et al. BMC Genomics 2013, 14:157 http://www.biomedcentral.com/1471-2164/14/Page 8 ofdevelopment, cell proliferation and apoptosis [37-40]. In the present study, eight members of the let-7 family (let7a, let-7b, let-7c, let-7d, let-7e, let-7f, let-7 g and let-7i) were expressed at high levels in both libraries, and let-7b was the most highly expressed miRNA in the ovaries of non-pregnant goats (normalized expression level of 246,928). Bioinformatics analysis indicated that let-7b may PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/29072704 bind to the Activin receptor I and Smad2/3 genes in the TGF-beta signaling pathway, and may affect follicular development and estrogen secretion (Figure 6C and D).from three 24-month old non-pregnant goats and six ovaries were from three 24 -month old pregnant goats. The ovaries were immersed in liquid nitrogen immediately after collection and stored at -80 . Total RNA was isolated using TRIzol reagent (Invitrogen, Carlsbad, CA, USA), according to the manufacturer’s instructions. The quality of the total RNA was checked using the Agilent 2100 Bioanalyzer system (Santa Clara, CA, USA) and the samples were stored at -80 until analysis.Small RNA library construction and sequencingConclusions MiRNA expression patterns vary in the ovaries of pregnant and non-pregnant goats. In total, 617 conserved and 7 putative miRNAs were detected, and 407 differentially expressed miRNAs were identified in pregnant and non-pregnant ovaries, suggesting that miRNAs may play an important role in the regulation of goat ovarian function. For example, miRNA-143 was strongly associated with reproduction, and may potentially regulate the Wnt/beta-catenin signaling pathway by targeting Frizzled-6 and -3. Let-7b may regulate the TGF-beta signaling pathway by targeting the Activin receptor and Smad2/3. Future work to characterize the expression of ovarian miRNAs at different stages of reproduction and in different breeds of goat, or in specific cell lines derived from ovarian tissues, is necessary to fully elucidate the functions of miRNAs in goat follicular development and hormone secretion, which will help to understand the AZD0156 site relationships between miRNAs and mammalian r.