Abstract
The placenta is a dynamic organ which undergoes extensive remodeling throughout pregnancy to support, protect and nourish the developing fetus. Despite the importance of the placenta, very little is known about its gene expression beyond very early pregnancy and post-partum. Therefore, we utilized RNA-sequencing to characterize the transcriptome from the fetal (chorioallantois) and maternal (endometrium) components of the placenta from mares throughout gestation (4, 6, 10, 11 m). Within the endometrium, 47% of genes changed throughout pregnancy, while in the chorioallantois, 29% of genes underwent significant changes in expression. Further bioinformatic analyses of both differentially expressed genes and highly expressed genes help reveal similarities and differences between tissues. Overall, the tissues were more similar than different, with ~ 95% of genes expressed in both tissues, and high similarities between the most highly expressed genes (9/20 conserved), as well as marked similarities between the PANTHER pathways identified. The most highly expressed genes fell under a few broad categories, including endocrine and immune-related transcripts, iron-binding proteins, extracellular matrix proteins, transport proteins and antioxidants. Serine protease inhibitors were particularly abundant, including SERPINA3, 6 and 14, as well as SPINK7 and 9. This paper also demonstrates the ability to effectively separate maternal and fetal components of the placenta, with only a minimal amount of chorioallantoic contamination in the endometrium (~8%). This aspect of equine placentation is a boon for better understanding gestational physiology and allows the horse to be used in areas where a separation of fetal and maternal tissues is essential. Overall, these data represent the first large-scale characterization of placental gene expression in any species and include time points from multiple mid- to late-gestational stages, helping further our understanding of gestational physiology.
Highlights
Pregnancy is dynamic with a continuous dialog between the conceptus and dam throughout gestation
Given the overall lack of knowledge about mid-gestational gene expression in the endometrial and trophoblastic placenta, we aimed to characterize the transcriptome of the chorioallantois and the endometrium throughout gestation to gain a better understanding of placental physiology and the complementary roles of fetal and maternal tissues during equine pregnancy
This study represents the first report based on next-generation sequencing to examine gene expression serially within the chorioallantois and the endometrium throughout mammalian gestation
Summary
Pregnancy is dynamic with a continuous dialog between the conceptus and dam throughout gestation. Most of the research directed toward the placenta over the past 40 years has focused primarily on either early or late pregnancy, with relatively little understanding of the physiology or gene expression of the mid-gestation placenta. This lack of mid-gestational studies is a problem in the horse, but across all placental mammals. In many species, including human and mouse, it is not possible to separate the maternal and fetal placenta due to hemochorial placentation, making it difficult to study the maternal-fetal interaction during gestation. The horse has epitheliochorial placentation, making it a suitable model for studying the fetal (chorioallantois) and maternal (endometrium) aspects of the placenta, including maternal response
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