Conceptus-Induced Changes in the Endometrial Transcriptome: How Soon Does the Cow Know She Is Pregnant?1

Abstract

This study sought to determine the earliest response of the bovine uterine endometrium to the presence of the conceptus at key developmental stages of early pregnancy. There were no detectable differences in gene expression in endometria from pregnant and cyclic heifers on Days 5, 7, and 13 postestrus, but the expression of 764 genes was altered due to the presence of the conceptus at maternal recognition of pregnancy (Day 16). Of these 514 genes, MX2, BST2, RSAD2, ISG15, OAS1, USP18, IFI44, ISG20, SAMD9, EIF4E, and IFIT2 increased to the greatest extent in pregnant endometria (>8-fold log2 fold change increase). The expression of OXTR, Bt.643 (unofficial symbol), and KCNMA1 was reduced the most, but short-term treatment with recombinant ovine interferon tau (IFNT) in vitro or in vivo did not alter their expression. In vivo intrauterine infusion of IFNT induced the expression of EIF4E, IFIT2, IFI44, ISG20, MX2, RSAD2, SAMD9, and USP18. These results revealed for the first time that changes that occur in the endometrial transcriptome are independent of the presence of a conceptus until pregnancy recognition. The differentially expressed genes (including MX2, BST2, RSAD2, ISG15, OAS1, USP18, IFI44, ISG20, SAMD, and EIF4E) are a consequence of IFNT production by the conceptus. The identified genes represent known and novel early markers of conceptus development and/or return to cyclicity and may be useful to identify the earliest stage at which the endometrial response to the conceptus is detectable.

Maternal-embryo interaction leading up to the initiation of implantation of pregnancy in cattle

“…In both cyclic and pregnant animals, similar changes occur in endometrial gene Maternal-embryonic interaction in early pregnancy expression up to initiation of conceptus elongation (approximately Day 13), suggesting that the default mechanism in the uterus is to prepare for, and expect, pregnancy (Forde et al, 2011b). Indeed, as mentioned above, it is possible to transfer an embryo to a synchronous uterus 7 days after oestrus and establish a pregnancy, as is routine in commercial bovine embryo transfer, and even up to Day 16.…”

“…It is only when IFNT secretion from the conceptus is sufficient to induce the pregnancy recognition response in both the endometrium and in the extra uterine environment, that divergences between the pregnant and non-pregnant uterus are established. In general, these differences are detectable by Day 15 or Day 16 of pregnancy (Forde et al, 2011b;Bauersachs et al, 2012) and the major changes identified include response to a Type I Interferon, of which IFNT is one. This includes the up-regulation of 'classical' interferon-stimulated genes (ISGs) such as ISG15, (Johnson et al, 1998), MX1 and MX2 (Hicks et al, 2003), OAS1, BST2, B2M, CXCL10, STAT1, STAT2, PTX3, EIF4E, USP18 (Forde et al, 2011b) Indeed in the last number of years there have been quite a number of large transcriptomic studies performed on gene expression changes in the endometrium of pregnancy compared with non-pregnant or cyclic heifers.…”

“…In general, these differences are detectable by Day 15 or Day 16 of pregnancy (Forde et al, 2011b;Bauersachs et al, 2012) and the major changes identified include response to a Type I Interferon, of which IFNT is one. This includes the up-regulation of 'classical' interferon-stimulated genes (ISGs) such as ISG15, (Johnson et al, 1998), MX1 and MX2 (Hicks et al, 2003), OAS1, BST2, B2M, CXCL10, STAT1, STAT2, PTX3, EIF4E, USP18 (Forde et al, 2011b) Indeed in the last number of years there have been quite a number of large transcriptomic studies performed on gene expression changes in the endometrium of pregnancy compared with non-pregnant or cyclic heifers. Despite the different platforms used for analysis, breed of animal and different data analysis methods Bauersachs et al (2012) used gene set enrichment analysis to reveal a conceptus-induced signature in the endometrium across numerous studies on Days 15, 16, 17, 18 and 20.…”

“…Indeed, as mentioned above, it is possible to transfer an embryo to a synchronous uterus 7 days after oestrus and establish a pregnancy, as is routine in commercial bovine embryo transfer, and even up to Day 16. It is only in association with maternal recognition of pregnancy, which occurs on approximately Day 16 in cattle, that significant changes in the transcriptomic profile are detectable between cyclic and pregnant endometria (Forde et al, 2011b;Bauersachs et al, 2012), when the endometrium responds to increasing amounts of interferon-tau (IFNT) secreted by the filamentous conceptus.…”

“…These are necessary to drive the changes required in the endometrium (and resulting histotroph), in order to provide the embryo/conceptus with the nutritional requirements it needs, which change as the embryo undergoes distinct morphological events. Data on the pre-hatching embryo indicate that the expression of a large number of genes and pathways (Forde et al, 2009(Forde et al, , 2011b(Forde et al, and 2012a, including aminopeptidase, lipoprotein lipase and lactotransferrin amino acids, ions and glucose (Hugentobler et al, 2007 and as well as proteins in the histotroph including Ezrin, triosephosphate isomerase, Glutathione S transferase mu, Cathepsin D, Annexin A1, which were more abundant in the histotroph than in circulation (Faulkner et al, 2012). This expression pattern is governed, in part, by the expression of the nuclear P4 receptor (PGR) in the LE and glandular epithelium (GE).…”