Identification and differential expression of microRNAs in the ovaries of pigs (Sus scrofa) with high and low litter sizes

Abstract

Litter size affects profitability in the swine industry. Mammalian ovaries play important roles during reproduction, including ovulation and hormone secretion, which are tightly regulated by specific microRNAs (miRNAs). In this study, we investigated the effects of specific miRNAs on porcine litter size. We compared the ovarian miRNAs of Yorkshire pigs with high (YH) and low (YL) litter sizes using Solexa sequencing technology. We identified 327 and 320 miRNAs in the ovaries of YH and YL pigs respectively. A total of 297 miRNAs were co-expressed; 30 and 23 miRNAs respectively were specifically expressed in the two libraries. A total of 83 novel miRNAs were predicted; 37 specific miRNAs were obtained, of which 21 miRNAs were upregulated and 16 miRNAs were downregulated in YH compared with YL. Additionally, 19 628 and 19 250 target genes were predicted in the two libraries respectively. The results revealed that specific miRNAs (i.e., miR-224, miR-99a, let-7c, miR-181c, miR-214 and miR-21) may affect porcine litter size. The results of this study will help in gaining understanding of the role of miRNAs in porcine litter size regulation.

Identification and comparative analysis of the ovarian microRNAs of prolific and non-prolific goats during the follicular phase using high-throughput sequencing

“…These results indicate that the high-throughput sequencing data were highly enriched for small RNA sequences. These sequencing data are consistent with previous findings in mice 32 , pigs 22 , goats 18–21 , and chickens 33 , but vary among bovine ovaries, where the 20-nt size was the most abundant, followed by 22 nt 34, 35 , likely reflecting species differences.…”

“…The 10 most highly expressed miRNAs (miR-99a, miR-148a, miR-143, miR-10b, miR-26a, miR-21, miR-125b, miR-27b, let-7f, and miR-101) identified in the present study were also highly expressed in the ovaries of goats 18, 20 , pigs 22 , and other animal species as reviewed by Li et al . 9 .…”

“…In total, 142 novel miRNAs were detected from the prolific JTG and non-prolific TBG libraries, which is distinctly higher than the amount predicted in the ovaries of polytocous compared with monotocous goats 19, 20 and pigs with high and low litter sizes 22 . Analysis of the sequencing data resulted in the identification of 191 unique miRNAs, which were significantly differentially expressed between the prolific JTG and non-prolific TBG libraries.…”

“…miR-99a has been shown to be one of the most predominant miRNA populations in mammalian ovaries 18, 22, 41 ; it induces G1-phase cell cycle arrest and suppresses tumourigenicity 44 , which may play critical roles in normal ovarian functions. miR-125b suppresses proapoptotic protein expression 45 , and androgens attenuate follicular atresia through nuclear and extranuclear signalling pathways by enhancing miR-125b expression, which in turn suppresses proapoptotic protein expression 46 .…”

“…miRNAs abundant in the extracellular vesicles (EVs) of small bovine follicles were associated with cell proliferation pathways, whereas miRNAs abundant in large follicles were related to inflammatory response pathways 17 . A large number of differentially expressed known and novel miRNAs have also been identified and comparatively analyzed in the ovaries of goats that are pregnant vs. non-pregnant 18 or have high vs. low kidding rates 19–21 and in pigs with high vs. low litter sizes 22 . For example, Miao et al .…”