Integrated multiple transcriptomes in oviductal tissue across the porcine estrous cycle reveal functional roles in oocyte maturation and transport

Abstract

Understanding the changes in the swine female reproductive system is important for solving issues related to reproductive failure and litter size. Elucidating the regulatory mechanisms of the natural estrous cycle in the oviduct under non-fertilisation conditions can improve our understanding of its role in the reproductive system. Herein, whole transcriptome RNA sequencing of oviduct tissue samples was performed. The differentially expressed genes (DEGs) were identified for each time point relative to day 0 and classified into three clusters based on their expression patterns. Clusters 1 and 2 included genes involved in the physiological changes through the estrous cycle. Cluster 1 genes were mainly involved in PI3K-Akt signaling and steroid hormone biosynthesis pathways. Cluster 2 genes were involved in extracellular matrix-receptor interactions and protein digestion pathways. In Cluster 3, the DEGs were downregulated in the luteal phase; they were strongly associated with cell cycle, calcium signaling, and oocyte meiosis. The gene expression in the oviduct during the estrous cycle influenced oocyte transport and fertilization. Our findings provide a basis for successfully breeding pigs and elucidating the mechanisms underlying the changes in the pig oviduct during the estrous cycle. © The Author(s) 2021. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.Understanding the swine female reproductive system is important for solving issues related to reproductive failure and litter size. The oviduct is the site of fertilization. After fertilization, the fertilized egg moves to the uterus for implantation. Elucidating the regulatory mechanisms of the estrous cycle in the oviduct can improve our understanding of their roles. In this study, whole transcriptome RNA sequencing of oviduct tissue samples was performed throughout the estrous cycle to screen for differentially expressed genes (DEGs). The DEGs were classified into three clusters based on their expression patterns. Clusters 1 and 2 included genes involved in the physiological changes observed through the estrous cycle. The expression levels of Cluster 3 genes were downregulated specifically in the luteal phase; this was associated with calcium signalling and oocyte meiosis. In this study, we identified that the expression of genes in the oviduct influences oocyte transport and fertilization, which are the key functions of the oviduct. This study provides a basis for successful breeding in the pig industry and elucidating the mechanisms underlying the changes in the pig oviduct during the estrous cycle.