Abstract
Improvement in litter size has become of great interest in the pig industry because fecundity is directly related to sow reproductive life. Improved reproduction has thus been achieved by elucidating the molecular functions of genes associated with fecundity. In the present study, we identified differentially expressed genes (DEGs) via transcriptomic analysis using RNA-sequencing (RNA-Seq) in Berkshire pig placentas from larger (LLG, mean litter size >12) and smaller (SLG, mean litter size < 6.5) litter size groups. In total 588 DEGs were identified (p < 0.05, > 1.5-fold change), of which 98 were upregulated, while 490 were downregulated in the LLG compared with the SLG. Gene Ontology (GO) enrichment was also performed. We concluded that 129 of the 588 DEGs were closely related to litter size according to reproduction related genes selected based on previous reports, as 110 genes were downregulated and 19 upregulated in the LLG compared with the SLG. RT-qPCR utilizing specific primers targeting the early growth response 2 (EGR2), pheromaxein c subunit (PHEROC) and endothelial lipase (LIPG) genes showed high accordance with RNA-Seq results. Furthermore, we investigated the upstream regulators of these three genes in the placenta. We found that WNT9B, a Wnt signaling pathway molecule, and IL-6, known inducers of EGR2 and LIPG, respectively, were significantly increased in LLG compared with SLG. We believe that the induction of IL-6 and LIPG may play an important role in increasing nutrition supply through the placenta from the sow to the piglet during gestation. These results provide novel molecular insights into pig reproduction.
Highlights
Improved litter size is a principal interest in the pig industry and among breeders
The expression of WNT11 mRNA was decreased and that of WNT9B was increased in litter size: the larger (LLG) compared with SLG, respectively (Fig 5C and 5D)
A total of 129 genes (19 upregulated genes and 110 downregulated genes in LLG compared with SLG) from the 588 differentially expressed genes (DEGs) were selected because they are associated with litter size [34,35,36,37]
Summary
Improved litter size is a principal interest in the pig industry and among breeders. Litter size is a complex trait composed of many subordinated traits, such as ovulation rate, embryonic/fetal. Since selection by litter size has its limitations, including low heritability and sex-restriction, various efforts have been made to identify factors influencing litter size. Improvement in the litter size of Berkshire pigs is essential for Berkshire pig breeders In this context, we hypothesized that DEGs in the placenta play a critical role in the determination of litter size. This study analyzed the RNA-Seq of Berkshire placentas, which revealed novel genes that may be involved in placental development and function, playing a role in determining litter size. These results provide molecular insights into the genes underlying pig fecundity
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