Transcriptional regulation of the bovine oxytocin receptor gene

Effects of conceptus proteins on endometrium and blood leukocytes of dairy cattle using transcriptome and meta-analysis

This study investigates the short and long-term effects of IFNT and PAG on the transcriptome of endometrium and blood leukocytes. Holstein heifers received intrauterine infusions of one of the following treatments: 20 mL of a 200 μg/mL bovine serum albumin solution (BSA; vehicle) from day 14 to 16 of the estrous cycle (BSA), vehicle + 10 μg/mL of IFNT from day 14 to 16 (IFNT3), vehicle + 10 μg/mL of IFNT from day 14 to 19 (IFNT6), and vehicle + 10 μg/mL of IFNT from day 14 to 16 followed by vehicle + 10 μg/mL of IFNT + 5 μg/mL of PAG from day 17 to 19 (IFNT+PAG). RNA-seq analysis was performed in endometrial biopsies and blood leukocytes collected after treatments. Acute IFNT signaling in the endometrium (IFNT3 vs BSA), induced differentially expressed genes (DEG) associated with interferon activation, immune response, inflammation, cell death, and inhibited vesicle transport and extracellular matrix remodeling. Prolonged IFNT signaling (IFNT6 vs IFNT3) altered gene expression related to cell invasion, retinoic acid signaling, and embryo implantation. In contrast, PAG induced numerous DEG in blood leukocytes but only 4 DEG in the endometrium. In blood leukocytes, PAG stimulated genes involved in development and TGFB signaling while inhibiting interferon signaling and cell migration. Overall, IFNT is a primary regulator of endometrial gene expression, while PAG predominantly affected the transcriptome of circulating immune cells during early pregnancy. Further research is essential to fully grasp the roles of identified DEG in both the endometrium and blood leukocytes.

Transcriptomic analysis of bovine endometrial epithelial cells in response to interferon tau and hormone stimulation

The embryonic loss during early stage of gestation is one of the major causes of infertility for domestic ruminants, causing huge economic losses to pasture. Maternal recognition of pregnancy and implantation are the crucial process for determining the successful establishment and development of pregnancy in cattle. The research on molecular mechanisms of pregnancy recognition will facilitate illustrating the complex process of pregnancy establishment and help to improve pregnancy outcomes. In this study, we performed transcriptomic analysis of primary bovine endometrial epithelial cells (BEND) with or without IFNT and hormones intervention through RNA sequencing. We eventually identified 608 differentially expressed genes (DEGs) including 409 up-regulated genes and 199 down-regulated genes in IFNT and hormones-treated group compared with control group. Gene Ontology (GO) enrichment analysis demonstrated that the majority of DEGs were implicated in immune system process, response to external stimulus, response to cytokine, regulation of response to stress. Results from KEGG analysis showed a significant enrichment of NOD-like receptor signaling pathway, antigen processing and presentation, necroptosis, oxidative phosphorylation, RIG-I-like receptor signaling pathway. Additionally, a set of promising candidate genes, including (USP18, STAT1, PSMB8, IFIH1, MX2, IFI44, DHX58, CASP8, DRAM1, CXCR4), were characterized by constructing an integrated interaction network. Specifically, the mRNA expression of HOXA11, PTGS1 and PTGS2 were remarkably suppressed by silencing DRAM1 under IFNT and hormone administration, thus speculating that DRAM1 might play a crucial role in early pregnancy by regulating endometrial function. The results of this study depicted a relatively comprehensive transcriptional profiles of BEND in response to IFNT and hormones, which contributes to a better understanding of gene interaction network and underlying regulatory mechanisms in endometrium of ruminants during early pregnancy.

Conceptus-induced, interferon tau-dependent gene expression in bovine endometrial epithelial and stromal cells†

Bovine endometrium consists of epithelial and stromal cells that respond to conceptus interferon tau (IFNT), the maternal recognition of pregnancy (MRP) signal, by increasing expression of IFN-stimulated genes (ISGs). Endometrial epithelial and stromal-cell-specific ISGs are largely unknown but hypothesized to have essential functions during pregnancy establishment. Bovine endometrial epithelial cells were cultured in inserts above stromal fibroblast (SF) cells for 6 h in medium alone or with IFNT. The epithelial and SF transcriptomic response was analyzed separately using RNA sequencing and compared to a list of 369 DEGs recently identified in intact bovine endometrium in response to elongating bovine conceptuses and IFNT. Bovine endometrial epithelial and SF shared 223 and 70 DEGs in common with the list of 369 endometrial DEGs. Well-known ISGs identified in the epithelial and SF were ISG15, MX1, MX2, and OAS2. DEGs identified in the epithelial but not SF included a number of IRF molecules (IRF1, IRF2, IRF3, and IRF8), mitochondria SLC transporters (SLC25A19, SLC25A28, and SLC25A30), and a ghrelin receptor. Expression of ZC3HAV1, an anti-retroviral gene, increased specifically within the SF. Gene ontology analysis identified the type I IFN signaling pathway and activation of nuclear factor kappa B transcription factors as biological processes associated with the epithelial cell DEGs. This study has identified biologically relevant IFNT-stimulated genes within specific endometrial cell types. The findings provide critical information regarding the effects of conceptus IFNT on specific endometrial compartments during early developmental processes in cattle.

Current perspectives on the short- and long-term effects of conventional dairy calf raising systems: a comparison with the natural environment

Although the neonatal and infancy period is short, it is well documented that the early neonatal environment is critical for appropriate physical, behavioral, and cognitive development that lasts into adulthood. Dairy calves are commonly removed from the dam shortly after birth and raised in individual housing and fed limited milk allowances (4 to 6 L/d) in commercial farms around the world (conventional raising). Individual housing was developed to promote health status and facilitate individual animal monitoring. However, it is associated with high labor demand, and early life social isolation is associated with cognitive and behavioral abnormalities. Recently, group housing and enhanced milk-feeding programs are being increasingly adopted by farms; these practices more closely resemble the social and nutritional environments in natural or seminatural environments when the calf is raised with the dam. Conventional raising may lead to short- and long-term effects when compared to calves raised with the dam or peers. Short-term effects of conventional raising include impaired social skills when introduced to novel peers, reduced consumption of novel feeds, increased activity in a novel environment, and signs of hunger associated with limited milk intake and poor growth during the preweaning period. Evidence also suggests that the long-term effects of conventional artificial raising systems include behavioral differences, such as lower social submissiveness, increased heart rate and cortisol when presented with a novel environment, and production differences such as milk yield and reproductive performance. However, research on the long-term effects of maternal, social, physical, and nutritional restrictions in early life is still limited and should be encouraged. More research is needed to determine the long-term effects of artificial raising systems (individual, group housing, dam-raised) on future behavior, cognition, performance, and health parameters in dairy calves.

Symposium review: Immunological detection of the bovine conceptus during early pregnancy

Infertility and subfertility reduce the economic viability of dairy production. Inflammation reduces conception rates in dairy cattle, but surprisingly little information exists about the populations and the functions of immune cells at the conceptus-maternal interface during the periattachment period in dairy cattle. Early pregnancy is accompanied by immune stimulation at insemination and conceptus secretion of IFN-τ, pregnancy-associated glycoproteins, prostaglandins, and other molecules whose effects on immune function during early pregnancy have not been determined. Our working hypothesis is that pregnancy induces changes in immune cell populations and functions that are biased toward immunological tolerance, tissue remodeling, and angiogenesis. This review summarizes current knowledge, starting with insemination and proceeding through early pregnancy, as this is the period of maximal embryo loss. Results indicated that early pregnancy is accompanied by a marked increase in the proportion of endometrial immune cells expressing markers for natural killer (CD335) cells and cytotoxic T cells (CD8) along with an increase in cells expressing major histocompatibility class II antigens (macrophages and dendritic cells). This is accompanied by increased abundance of mRNA for IL-15, a natural killer growth factor, and IL-10 in the endometrium during early pregnancy. Furthermore, expression of indoleamine 2,3 dioxygenase was 15-fold greater in pregnant compared with cyclic heifers at d 17, but then declined by d 20. This enzyme converts tryptophan to kynurenine, which alters immune function by creating a localized tryptophan deficiency and by activation of the aryl hydrocarbon receptor and induction of downstream tolerogenic mediators. Expression of the aryl hydrocarbon receptor is abundant in the bovine uterus, but its temporal and spatial regulation during early pregnancy have not been characterized. Pregnancy is also associated with increased expression of proteins known to inhibit immune activation, including programed cell death ligand-1 (CD274), lymphocyte activation gene-3 (CD223), and cytotoxic T-lymphocyte associated protein-4 (CD152). These molecules interact with receptors on antigen-presenting cells and induce lymphocyte tolerance. Current results support the hypothesis that early pregnancy signaling in dairy heifers involves changes in the proportions of immune cells in the endometrium as well as induction of molecules known to mediate tolerance. These changes are likely essential for uterine wall remodeling, placentation, and successful pregnancy.

Integration of molecules to construct the processes of conceptus implantation to the maternal endometrium

During the peri-implantation period, ruminant conceptuses go through rapid elongation, followed by their attachment to the uterine endometrial epithelial cells, during which interferon-tau (IFNT), a trophectodermal cytokine required for the process of maternal recognition of pregnancy, is expressed in a temporal and spatial manner. On day 22 (day 0 = day of estrus), 2 to 3 d after the initiation of bovine conceptus attachment to the uterine epithelium, when IFNT production begins to subside, the expression of molecules related to epithelial-mesenchymal transition, zinc finger E-box binding homeobox 1, snail family transcriptional repressor 2, N-cadherin, and vimentin was found in the trophectoderm. Through the use of in vitro coculture system with bovine trophoblast CT-1 and endometrial epithelial cells, a series of experiments have been conducted to elucidate mechanisms associated with the regulation of IFNT gene transcription and conceptus implantation, including epithelial-mesenchymal transition processes. Expression of IFNT, both up- and downregulation, during the peri-implantation period is tightly controlled. Cytokines and cell adhesion molecules such as epidermal growth factor, basic fibroblast growth factor, transforming growth factor beta, activin A, L-selectin-podocalyxin, and vascular cell adhesion molecule 1-integrin α4 expressed in utero all contribute to the initiation of epithelial-mesenchymal transition in the trophectoderm. These results indicate that conceptus implantation to the uterine endometrium proceeds while elongated conceptuses and endometria express cell adhesion molecules and their receptors, and the trophectoderm experiences epithelial-mesenchymal transition. Data accumulated suggest that while the conceptus and the endometrial epithelium adhere, trophectodermal cells must gain more flexibility for binucleate and possibly trinucleate cell formation during the peri-implantation period, and that understanding and constructing the conditions throughout implantation processes is key to improving ruminants' fertility.

Paracrine and endocrine actions of interferon tau (IFNT)

This review focuses on the paracrine and endocrine actions of interferon tau (IFNT) during pregnancy recognition and establishment in ruminants. Pregnancy recognition involves the suppression of the endometrial luteolytic mechanism by the conceptus to maintain progesterone production by the corpus luteum (CL). The paracrine antiluteolytic effects of conceptus-derived IFNT inhibit upregulation of oxytocin receptors in the endometrial epithelia of the uterus, thereby preventing the production of luteolytic prostaglandin F2 alpha (PGF2α) pulses. In the endometrium, IFNT induces or upregulates a large number of classical IFN-stimulated genes (ISGs) and regulates expression of many other genes in a cell-specific manner that are likely important for conceptus elongation, implantation and establishment of pregnancy. Further, IFNT has endocrine effects on extrauterine cells and tissues. In sheep, IFNT induces luteal resistance to PGF2α, thereby ensuring survival of the CL for maintenance of pregnancy. The ISGs induced in circulating peripheral blood mononuclear cells by IFNT may also be useful as an indicator of pregnancy status in cattle. An increased knowledge of IFNT and ISGs is important to improve the reproductive efficiency in ruminants.

Chronicling the discovery of interferon tau

It has been 38 years since a protein, now known as interferon tau (IFNT), was discovered in ovine conceptus-conditioned culture medium. After 1979, purification and testing of native IFNT revealed its unique antiluteolyic activity to prevent the regression of corpora lutea on ovaries of nonpregnant ewes. Antiviral, antiproliferative and immunomodulatory properties of native and recombinant IFNT were demonstrated later. In addition, progesterone and IFNT were found to act cooperatively to silence expression of classical interferon stimulated genes in a cell-specific manner in ovine uterine luminal and superficial glandular epithelia. But, IFNT signaling through a STAT1/STAT2-independent pathway stimulates expression of genes, such as those for transport of glucose and amino acids, which are required for growth and development of the conceptus. Further, undefined mechanisms of action of IFNT are key to a servomechanism that allows ovine placental lactogen and placental growth hormone to affect the development of uterine glands and their expression of genes throughout gestation. IFNT also acts systemically to induce the expression of interferon stimulated genes that influence secretion of progesterone by the corpus luteum. Finally, IFNT has great potential as a therapeutic agent due to its low cytotoxicity, anti-inflammatory properties and effects to mitigate diabetes, obesity-associated syndromes and various autoimmune diseases.

A novel polymorphism in the oxytocin receptor encoding gene (OXTR) affects milk fatty acid composition in Italian Mediterranean river buffalo

The oxytocin receptor, also known as OXTR, is a protein which functions as receptor for the hormone and neurotransmitter oxytocin and the complex oxytocin–oxytocin receptor plays an important role in the uterus during calving. A characterisation of the river buffalo OXTR gene, amino acid sequences and phylogenetic analysis is presented. The DNA regions of the OXTR gene spanning exons 1, 2 and 3 of ten Mediterranean river buffalo DNA samples were analysed and 7 single nucleotide polymorphisms were found. We focused on the g.129C > T SNP detected in exon 3 and responsible for the amino acid replacement CGCArg > TGCCys in position 353. The relative frequency of T allele was of 0·257. An association study between this detected polymorphism and milk fatty acids composition in Italian Mediterranean river buffalo was carried out. The fatty acid composition traits, fatty acid classes and fat percentage of 306 individual milk samples were determined. Associations between OXTR g.129C > T genotype and milk fatty acids composition were tested using a mixed linear model. The OXTR CC genotype was found significantly associated with higher contents of odd branched-chain fatty acids (OBCFA) (P < 0·0006), polyunsaturated FA (PUFA n 3 and n 6) (P < 0·0032 and P < 0·0006, respectively), stearic acid (C18) (P < 0·02) and lower level of palmitic acid (C16) (P < 0·02). The results of this study suggest that the OXTR CC animals might be useful in selection toward the improvement of milk fatty acid composition.

Molecular characterization of oxytocin receptor gene in water buffalo (Bubalus bubalis)

Buffaloes are known for their productivity as compared to average yielding cows due to higher fat percentage, better feed conversion ability and disease resistance. On the other hand, the reproductive performances of buffaloes are often considered as poor owing to late sexual maturity, weak/silent oestrus, repeat breeder and prolonged intercalving interval. The study of cascade of events during oestrus and oestrous cycle can be useful for the improvement of reproductive efficiency of buffaloes. More precisely, the hormonal changes initiated at the molecular level within the animal determine the reproductive nature of the species. Nucleotide/protein sequence analysis serves as a vital tool in analysing the binding of the hormones for their effect or functions. In this study, we have reported cloning and characterization of the complete coding (cDNA) sequence of oxytocin receptor gene (OXTR) in buffaloes. Buffalo OXTR gene contains an uninterrupted ORF of 1176 nucleotides corresponding to an inferred polypeptide length of 391 amino acids (aa). The molecular weight of the deduced aa sequence was found to be 43 kDa with an isoelectric point of 9.253 and 16.328 charge at pH 7.0. The deduced protein sequence consists of 38 strongly basic (+) (K,R), 22 strongly acidic (-) (D,E), 186 hydrophobic (A, I, L, F, W, V) and 95 Polar (N, C, Q, S, T, Y) aa. Results indicated that aspartate (D) at aa position 85 and D, R and C at aa positions 136, 137 and 138, respectively, are conserved in buffaloes. The buffalo OXTR gene shared a per cent similarity ranging from 84.7 to 98.1 and 88.5 to 97.7 at nucleotide and deduced aa sequence levels, respectively, with that of other species. Phylogram constructed on the basis of either nucleotide or deduced aa sequences of buffalo OXTR gene showed that buffalo, cattle and sheep have diverged from human and swine and formed a separate clad. The buffalo sequence has shown maximum similarity and closeness with cattle followed by sheep both at nucleotide and at aa level.

Non-classical mechanisms of steroid sensing in the ovary: lessons from the bovine oxytocin model

Steroidogenic tissues such as the ovary, testes or adrenal glands are paradoxical in that they often indicate actions of steroid hormones within a dynamic range of ligand concentration in a high nanomolar or even micromolar level, i.e. at the natural concentrations existing within those organs. Yet ligand-activated nuclear steroid receptors act classically by direct interaction with DNA in the picomolar or low nanomolar range. Moreover, global genomic studies suggest that less than 40% of steroid-regulated genes involve classical responsive elements in gene promoter regions. The bovine oxytocin gene is a key element in the maternal recognition of pregnancy in ruminants and is regulated via an SF1 site in its proximal promoter. This gene is also regulated by steroids acting in a non-classical manner, involving nuclear receptors which do not interact directly with DNA. Dose-response relationships for these actions are in the high nanomolar range. Similar 'steroid sensing' mechanisms may prevail for other SF1-regulated genes and predict alternative pathways by which environmental endocrine disruptors might influence the functioning of steroid-producing organs and hence indirectly the steroid-dependent control of physiology and development.

Hosting the preimplantation embryo: potentials and limitations of different approaches for analysing embryo - endometrium interactions in cattle

Ongoing detailed investigations into embryo–maternal communication before implantation reveal that during early embryonic development a plethora of events are taking place. During the sexual cycle, remodelling and differentiation processes in the endometrium are controlled by ovarian hormones, mainly progesterone, to provide a suitable environment for establishment of pregnancy. In addition, embryonic signalling molecules initiate further sequences of events; of these molecules, prostaglandins are discussed herein as specifically important. Inadequate receptivity may impede preimplantation development and implantation, leading to embryonic losses. Because there are multiple factors affecting fertility, receptivity is difficult to comprehend. This review addresses different models and methods that are currently used and discusses their respective potentials and limitations in distinguishing key messages out of molecular twitter. Transcriptome, proteome and metabolome analyses generate comprehensive information and provide starting points for hypotheses, which need to be substantiated using further confirmatory methods. Appropriate in vivo and in vitro models are needed to disentangle the effects of participating factors in the embryo–maternal dialogue and to help distinguish associations from causalities. One interesting model is the study of somatic cell nuclear transfer embryos in normal recipient heifers. A multidisciplinary approach is needed to properly assess the importance of the uterine milieu for embryonic development and to use the large number of new findings to solve long-standing issues regarding fertility.

Quantitative characterization of prostaglandins in the uterus of early pregnant cattle

Prostaglandins (PGs) are important regulators of reproductive processes including early embryonic development. We analyzed the most relevant PG in bovine uteri at different preimplantation pregnancy stages when compared with non-pregnant controls. Additionally, endometrium and trophoblast tissues were examined regarding specific enzymes and receptors involved in PG generation and function. Simmental heifers were artificially inseminated or received seminal plasma only. At days 12, 15, or 18, post-estrus uteri were flushed for PG determination by liquid chromatography–tandem mass spectrometry. Endometrium and trophoblast tissues were sampled for RNA extraction and quantitative real-time PCR analysis. At all days and points of time examined, the concentration of 6-keto PGF1α (stable metabolite of PGI2) was predominant followed by PGF2α>PGE2>PGD2≈TXB2 (stable metabolite of TXA2). At days 15 and 18, PG increased from overall low levels at day 12, with a much more pronounced increase during pregnancy. The PGF2α/PGE2 ratio was not influenced by status. The highest PG concentration was measured at day 15 with 6-keto PGF1α (6.4 ng/ml) followed by PGF2α (1.1 ng/ml) and PGE2 (0.3 ng/ml). Minor changes in endometrial PG biosynthesis enzymes occurred due to pregnancy. Trophoblasts revealed high transcript abundance of general and specific PG synthases contributing to uterine PG. As PGI2 and PGF2α receptors were abundantly expressed by the trophoblast, abundant amounts of PGI2 and PGF2α in the uterine lumen point towards an essential role of PG for the developing embryo. High amounts of PG other than PGE2 in the preimplantation uterus may be essential rather than detrimental for successful reproduction.

Corpus luteum-endometrium-embryo interactions in the dairy cow: underlying mechanisms and clinical relevance

Conception rates of dairy cows are currently declining at an estimated 1% every year. Approximately, 35% of embryos fail to prevent luteolysis during the first three weeks of gestation. Interactions between the corpus luteum, endometrium and embryo are critical to the successful establishment of pregnancy and inadequacies will result in the mortality of the embryo. For example, as little as a one day delay in the post-ovulatory rise of progesterone has serious consequences for embryo development and survival. Recently, we found that LH support, degree of vascularization and luteal cell steroidogenic capacity were not the major factors responsible for this luteal inadequacy, but are nevertheless essential for luteal development and function. Progesterone acting on its receptor in the endometrium stimulates the production of endometrial secretions on which the free-living embryo is dependent. However, their exact composition and effects of inadequate progesterone remains to be determined. The embryo is recognized through its secretion of interferon tau (IFNT), which suppresses luteolytic pulses of prostaglandin F(2 alpha). In the cow, it is most likely that IFNT inhibits oxytocin receptor up-regulation directly and does not require the prior inhibition of oestrogen receptor alpha (ESR1). Unravelling the precise luteal-endometrium and embryo interactions is essential for us to understand pregnancy establishment and development of strategies to reverse the declining fertility of dairy cows.

Upregulations of Gata4 and oxytocin receptor are important in cardiomyocyte differentiation processes of P19CL6 cells

Oxytocin induces P19 cells to differentiate into cardiomyocytes possibly through the oxytocin/oxytocin receptor system. We added oxytocin to the growth medium of P19CL6, a subline of P19, but they did not differentiate into cardiomyocytes as indicated by RT-PCR and Western blotting results. During the cardiac commitment time of P19CL6 cells, the mRNA expression levels of the oxytocin receptor were upregulated by the addition of oxytocin as well as DMSO, but an upregulation of Gata4 expression levels was only observed for the cells induced by DMSO. The in silico analysis of the upstream sequence of the oxytocin receptor predicted putative binding sites for Gata4 and Nkx2.5. These results suggest that upregulations of the oxytocin receptor and Gata4 are important for cardiomyocyte differentiation processes.

The novel human gene MIP functions as a co-activator of hMafF

The human transcription factor MafF (hMafF) lacks a transactivation domain, it contains a heptad-leucine repeat motif (viz., Leu-zipper) that may mediate protein-protein interactions to regulate transcriptional activities. A protein with a coiled-coil domain encoded by a novel human gene (GenBank Accession No. AF289559) was found to interact with hMafF in vitro and in vivo and is designated as a MafF interacting protein (MIP). Here, we provide evidence that the coiled-coil domain of MIP is essential for binding to the Leu-zipper of hMafF and that the interaction between MIP and hMafF causes the translocalization of MIP from cytoplasm to nucleolus in HELA cells. We used a promoter-reporter system containing six tandem repeats of the US2 element, located in the promoter of the human oxytocin receptor gene and reported to bind specifically to hMafF, to understand effects on transcriptional activation of hMafF, and its interaction with MIP. Expression of hMafF or MIP alone did not alter basal reporter transcription activity, whereas co-expression of hMafF and MIP activated transcription efficiently. Moreover, truncated MIP, still containing the coiled-coil domain, transactivated as well as the full-length MIP did, and highlighting that MIP acts as a co-activator of hMafF.

Estrogen regulates transcription of the ovine oxytocin receptor gene through GC-rich SP1 promoter elements

Establishment of pregnancy in ruminants results from paracrine signaling by interferon tau (IFNT) from the conceptus to uterine endometrial luminal epithelia (LE) that prevents release of luteolytic prostaglandin F(2alpha) pulses. In cyclic and pregnant ewes, progesterone down-regulates progesterone receptor (PGR) gene expression in LE. In cyclic ewes, loss of PGR allows for increases in estrogen receptor alpha (ESR1) and then oxytocin receptor (OXTR) gene expression followed by oxytocin-induced prostaglandin F(2alpha) pulses. In pregnant ewes, IFNT inhibits transcription of the ESR1 gene, which presumably inhibits OXTR gene transcription. Alternatively, IFNT may directly inhibit OXTR gene transcription. The 5' promoter/enhancer region of the ovine OXTR gene was cloned and found to contain predicted binding sites for activator protein 1, SP1, and PGR, but not for ESR1. Deletion analysis showed that the basal promoter activity was dependent on the region from -144 to -4 bp that contained only SP1 sites. IFNT did not affect activity of the OXTR promoter. In cells transfected with ESR1, E2, and ICI 182,780 increased promoter activity due to GC-rich SP1 binding sites at positions -104 and -64. Mutation analyses showed that the proximal SP1 sites mediated ESR1 action as well as basal activity of the promoter. In response to progesterone, progesterone receptor B also increased OXTR promoter activity. SP1 protein was constitutively expressed and abundant in the LE of the ovine uterus. These results support the hypothesis that the antiluteolytic effects of IFNT are mediated by direct inhibition or silencing of ESR1 gene transcription, thereby precluding ESR1/SP1 from stimulating OXTR gene transcription.