Transcriptional Profiling of Equine Conceptuses Reveals New Aspects of Embryo-Maternal Communication in the Horse1

Abstract

Establishment and maintenance of pregnancy are critically dependent on embryo-maternal communication during the preimplantation period. The horse is one of the few domestic species in which the conceptus-derived pregnancy recognition signal has not been identified. To gain new insights into the factors released by the equine conceptus, transcriptional profiling analyses of conceptuses retrieved 8, 10, 12, and 14 days after ovulation were performed using a whole-genome microarray. Selected array data were confirmed using quantitative PCR, and the expression of proteins of interest was confirmed using immunohistochemistry and Western blotting. Gene ontology classification of differentially regulated transcripts underlines the ongoing embryo-maternal dialogue. Transcript showing higher expression levels as conceptus' development proceeds mainly localizes to the extracellular environment, thereby having the potential to act upon the uterine environment. Genes involved in the positive regulation of the immune system are enriched among transcripts displaying decreased expression, reflecting the need of the semiallograft conceptus to be protected from the immune system. A subset of differentially expressed genes, such as BRCA1 and FGF2, has previously been described to be expressed by early stages of embryonic development, whereas other transcripts are apparently unique to equine conceptuses, as their expression has not been reported in other species. These transcripts include fibrinogen subunits, the expressions of which were confirmed at the mRNA and protein level. Furthermore, results indicate the counteraction of trophoblast invasion, and that the conceptus appears to regulate changes in sialic acid content of its capsule, an event suggested to be essential for successful establishment of pregnancy.

Pregnancy Recognition and Implantation of the Conceptus in the Mare

“…Similar to the expression pattern of STAR, cytochrome P450 cholesterol side-chain cleavage enzyme (P450SCC) transcript abundance increases with age of conceptus; P450SCC catalyzes the conversion of cholesterol to pregnenolone (Klein and Troedsson 2011 ). Then 3-beta-hydroxysteroid dehydrogenase (HSD3B1), a key enzyme in the production of progesterone, androgen, and estrogen, is expressed by cells of the trophectoderm/chorion (Flood and Marrable 1975 ), and, like STAR and HSD3B1, expression increases with stage of conceptus development (Klein and Troedsson 2011 ). CYP19A1, commonly known as aromatase, catalyzes the last steps of estrogen biosynthesis and is expressed by trophectoderm and extraembryonic endoderm just beneath the embryonic disk (Walters et al 2000 ).…”

“…The trophoblast and not the endometrium is the source of capsular material, as evident through xenogeneic transplantation of trophoblast and endometrium into immunodefi cient mice (Albihn et al 2003 ). Indeed, transcriptional profi ling of equine conceptuses revealed developmentally regulated expression of a sialic acid transporter and sialyltransferases (Klein and Troedsson 2011 ). By Day 22, the capsule disappears, but the responsible mechanism remains unknown (Oriol et al 1993b ).…”

“…The rate-limiting step in the production of steroid hormones is the transfer of cholesterol within mitochondria to the inner mitochondrial membrane by steroidogenic acute regulatory protein (STAR), and equine conceptuses increase expression of STAR with advancing stage of development (Klein and Troedsson 2011 ). Similar to the expression pattern of STAR, cytochrome P450 cholesterol side-chain cleavage enzyme (P450SCC) transcript abundance increases with age of conceptus; P450SCC catalyzes the conversion of cholesterol to pregnenolone (Klein and Troedsson 2011 ).…”

“…The rate-limiting step in the production of steroid hormones is the transfer of cholesterol within mitochondria to the inner mitochondrial membrane by steroidogenic acute regulatory protein (STAR), and equine conceptuses increase expression of STAR with advancing stage of development (Klein and Troedsson 2011 ). Similar to the expression pattern of STAR, cytochrome P450 cholesterol side-chain cleavage enzyme (P450SCC) transcript abundance increases with age of conceptus; P450SCC catalyzes the conversion of cholesterol to pregnenolone (Klein and Troedsson 2011 ). Then 3-beta-hydroxysteroid dehydrogenase (HSD3B1), a key enzyme in the production of progesterone, androgen, and estrogen, is expressed by cells of the trophectoderm/chorion (Flood and Marrable 1975 ), and, like STAR and HSD3B1, expression increases with stage of conceptus development (Klein and Troedsson 2011 ).…”

Trophoblast of domestic and companion nimals: basic and applied clinical perspectives

“…However, the embryo moves continuously throughout the uterine lumen before fixation and implantation at around days 20-22 (Ginther, 1985) and this continuous movement helps in exerting the antiluteolytic effect on the uterus thus preventing the cyclic secretion of uterine PGF2α and helping in maintaining the pregnancy (Allen and Wilsher, 2009). The inhibition of PGF2α has been attributed to the reduced expression of cyclooxygenase-2 and has been suggested to be a target of conceptus derived antiluteolytic mechanism in horses (Klein and Troedsson, 2011b). Unlike ruminants, interferon-like molecules as produced by ruminant trophoblast have not been reported from the equine trophoblast.…”