Isolation and Sequence of an Interferon-τ-Inducible, Pregnancy- and Bovine Interferon-Stimulated Gene Product 15 (ISG15)-Specific, Bovine Ubiquitin-Activating E1-Like (UBE1L) Enzyme1

Conceptus-modulated innate immune function during early pregnancy in ruminants: a review

This review focuses on the innate immune events modulated by conceptus signaling during early pregnancy in ruminants. Interferon-tau (IFN-τ) plays a role in the recognition of pregnancy in ruminants, which involves more than the inhibition of luteolytic pulses of PGF2α to maintain corpus luteum function. For successful pregnancy establishment, the allogenic conceptus needs to prevent rejection by the female. Therefore, IFN-τ exerts paracrine and endocrine actions to regulate the innate immune system and prevent conceptus rejection. Additionally, other immune regulators work in parallel with IFN-τ, such as the pattern recognition receptors (PRR). These receptors are activated during viral and bacterial infections and in early pregnancy, but it remains unknown whether PPR expression and function are controlled by IFN-τ. Therefore, this review focuses on the main components of the innate immune response that are involved with early pregnancy and their importance to avoid conceptus rejection.

Changes in expression of interferon-stimulated genes and ubiquitin activating enzyme E1-like in ovine thymus during early pregnancy

As the main signal for the maternal recognition in ruminants, interferon-tau (IFNT) stimulates expression of interferon-stimulated genes (ISGs) in uterus and many extrauterine tissues. However, it is unclear that early pregnancy induces expression of signal transducer and activator of transcription 1 (STAT1), myxovirusresistance 1 (Mx1), interferon-gamma-inducible protein 10 (IP-10) and ubiquitin activating enzyme E1-like protein (UBE1L) in maternal thymus. In this study, ovine thymuses were sampled on day 16 of the estrous cycle and on days 13, 16 and 25 of gestation, and the expression of STAT1, Mx1, IP-10 and UBE1L was detected by real-time quantitative PCR, Western blot and immunohistochemistry. The results revealed that the expression of STAT1 and IP-10 reached peaks on day 16 of pregnancy, and expression of Mx1 was enhanced on day 25 of pregnancy, and STAT1 protein was located in the epithelial reticular cells, capillaries and thymic corpuscles. However, expression of UBE1L was declined during early pregnancy. In conclusion, early pregnancy influences expression of STAT1, Mx1, IP-10 and UBE1L in maternal thymus, which may participate in regulation of maternal immune tolerance during early pregnancy in sheep.

In silico characterization of interferon-stimulated gene (ISG15) as a biomarker for early pregnancy diagnosis in Bubalus bubalis

Reproductive management of livestock is the foremost requirement for increasing production from any dairy animal. High reproductive efficiency can be achieved by implementation of one of the crucial management practices which involves early differentiation of pregnant and non-pregnant animals. The early and precise pregnancy diagnosis is the major problem in Bubalus bubalis (buffalo) due to absence of estrous signs instead of normal cyclicity of reproductive organs. Therefore, in the present study, one of the conceptus derived protein interferon stimulated protein (15 kDa) released during 18 to 21 days after insemination in response to implantation of embryo was in silico characterized. The protein expressed by interferon-stimulated gene-15 (ISG15) was analyzed by isolation and sequencing of coding region of mRNA. The primary and secondary structures were predicted from the protein sequence to decipher the interaction of ISG15 protein with other molecules. The functional characterization identifies various motifs present in ISG15 protein which are responsible for its interaction with other proteins. Physiochemical properties predicted the ISG15 protein nature during in vitro conditions which are required for any of the assays development. In addition, immunogenic studies revealed ISG15 protein is strongly antigenic in nature and can be used for antibody production. In conclusion, ISG15 protein expression from buffalo is a good indicator of conceptus implantation and has suitable properties for being used as target to develop early pregnancy diagnostic kits.

Recombinant interferon stimulated protein 15 (rISG15) as a molecular marker for detection of early pregnancy in Bubalus bubalis

Early and accurate diagnosis of pregnancy in animals is important for improving the reproductive management of livestock. The buffalo (Bubalus bubalis) is the most important dairy animal in India, but there are reproductive problems resulting from extended calving interval and ovulation occurring in the absence of behavioral estrus. The lack of simple methods for early pregnancy diagnosis intensifies these problems. The present study, therefore, was conducted to ascertain the role of the interferon-stimulated gene, (ISG), 15 in pregnancy detection. The anti-ISG15 Mab based ELISA was developed that could be used for detecting pregnancy at 18 to 20 days after artificial insemination (AI). The ISG15 protein was isolated from a pregnant buffalo and was amplified, and cloned in Escherichia coli by using coding region primers. The ISG15 gene was expressed in the host Escherichia coli BL21 (DE3), and the protocol was standardized for optimum gene expression. Using immortal hybridoma (fused myeloma and B cells) cells, a highly specific and sensitive antibody, anti-ISG15 mAb, for detecting ISG15 (protein) in the serum of pregnant buffaloes was obtained. A blocking ELISA was developed using the anti-ISG15 mAb to detect pregnancy in buffalo within 18 to 21 days after AI. The ISG15 gene was upregulated (P <  0.05) in pregnant buffalo at 18 to 21 days of pregnancy. This assay has an overall diagnostic accuracy of 75.0%. It, therefore, is concluded that recombinant ISG15 retains the potential for detecting pregnancy in B. bubalis and may have applications in ELISA kits for pregnancy detection in closely related species.

Pregnancy-induced changes in metabolome and proteome in ovine uterine flushings

Mass spectrometry (MS) approaches were used herein to identify metabolites and proteins in uterine flushings (UF) that may contribute to nourishing the conceptus. Ovine uteri collected on Day 12 of the estrous cycle (n = 5 ewes exposed to vasectomized ram) or Days 12 (n = 4), 14 (n = 5), or 16 (n = 5) of pregnancy (bred with fertile ram) were flushed using buffered saline. Metabolites were extracted using 80% methanol and profiled using ultraperformance liquid chromatography (LC) tandem mass spectrometry. The proteome was examined by digestion with trypsin, followed by the analysis of peptides with LC-MS/MS. Metabolite profiling detected 8510 molecular features of which 9 were detected only in UF from Day 14-16 pregnant ewes that function in fatty acid transport (carnitines), hormone synthesis (androstenedione like), and availability of nutrients (valine). Proteome analysis detected 783 proteins present by Days 14-16 of pregnancy in UF, 7 of which are as follows: annexin (ANX) A1, A2, and A5; calcium-binding protein (S100A11); profilin 1; trophoblast kunitz domain protein 1 (TKDP); and interferon tau (IFNT). These proteins function in endocytosis, exocytosis, calcium signaling, and inhibition of prostaglandins (annexins and S100A11); protecting against maternal proteases (TKDP); remodeling cytoskeleton (profilin 1); and altering uterine release of prostaglandin F2 alpha as well as inducing IFNT-stimulated genes in the endometrium and the corpus luteum (IFNT). Identifying metabolites and proteins produced by the uterus and conceptus advances our understanding of embryo/maternal signaling and provides insights into possible the causes of reproductive failure.

Cloning and Sequence Analysis of Wild Argali ISG15 cDNA

The complete coding sequence of Wild Argali ISG15 cDNA was generated by rapid amplification of cDNA ends. The ISG15 cDNA was 642 bp with an open reading frame of 474 bp, which encoded a 17.47 kDa protein composed of 157 amino acids. Its amino acid sequence shared 97.9%, 80.8%, 91.4%, 94.3%, 78.3% identity with those of ISG15cDNA from Ovis aries (accession no. NM001009735.1), Capra hircus (accession no. HQ329186.1), Bos taurus (accession no. BC102318.1), Bubalus bubalis (accession no. HM543269.1), and Sus scrofa (accession no. EU647216.1), respectively. The entire coding sequence was inserted into the pET-28a vector and expressed in E. coli. The recombinant protein corresponded to the expected molecular mass of 25 kDa as judged by SDS-PAGE, and it was detected in the bacterial inclusion bodies. The expressed protein could be purified by Ni²⁺ chelate affinity chromatography and the results from the lymphocyte proliferation test showed that the product could stimulate lymphocyte proliferation very well (p<0.05), which further confirmed its biological activity.

ISGylation: a conserved pathway in mammalian pregnancy

Successful pregnancy includes remodeling and differentiation of the endometrium in response to sex steroid hormones, development of maternal immunotolerance to the implanting embryo, and modification of the local uterine environment by the embryo to suit its own needs. The major signal released by the ruminant conceptus during establishment of pregnancy is interferon-tau (IFNT) that stimulates the expression of many genes in the endometrium and ovary. One of these genes is called interferon stimulated gene 15 (ISG15), which encodes a ubiquitin homolog with a C-terminal Gly that becomes covalently attached to Lys residues on targeted proteins through an ATP-dependent multi-step enzymatic reaction called ISGylation. The conceptus-derived induction of endometrial ISGs also occurs in mouse and human deciduas and placenta, in response to pregnancy presumably through action of cytokines such as interleukins and type I IFN. Described herein is evidence to support the concept that ISGylation is a maternal response to the developing conceptus, implantation and placentation that is conserved across mammalian pregnancy. Although the precise role for ISG15 remains elusive during pregnancy, it is clear that up-regulation in response to pregnancy may impart a pre-emptive defense to infection or other environmental insults, and protection of the conceptus against inflammatory insults across species.

Pregnancy-associated genes contribute to antiluteolytic mechanisms in ovine corpus luteum

The hypothesis that ovine luteal gene expression differs due to pregnancy status and day of estrous cycle was tested. RNA was isolated from corpora lutea (CL) on days 12 and 14 of the estrous cycle (NP) or pregnancy (P) and analyzed with the Affymetrix bovine microarray. RNA also was isolated from luteal cells on day 10 of estrous cycle that were cultured for 24 h with luteolytic hormones (OXT and PGF) and secretory products of the conceptus (IFNT and PGE2). Differential gene expression (>1.5-fold, P < 0.05) was confirmed using semiquantitative real-time PCR. Serum progesterone concentrations decreased from day 12 to day 15 in NP ewes (P < 0.05) reflecting luteolysis and remained >1.7 ng/ml in P ewes reflecting rescue of the CL. Early luteolysis (days 12-14) was associated with differential expression of 683 genes in the CL, including upregulation of SERPINE1 and THBS1. Pregnancy on day 12 (55 genes) and 14 (734 genes) also was associated with differential expression of genes in the CL, many of which were ISGs (i.e., ISG15, MX1) that were induced when culturing luteal cells with IFNT, but not PGE2. Finally, many genes, such as PTX3, IL6, VEGF, and LHR, were stabilized during pregnancy and downregulated during the estrous cycle and in response to culture of luteal cells with luteolytic hormones. In conclusion, pregnancy circumvents luteolytic pathways and activates or stabilizes genes associated with interferon, chemokine, cell adhesion, cytoskeletal, and angiogenic pathways in the CL.

Differential neutrophil gene expression in early bovine pregnancy

BACKGROUND

In food production animals, especially cattle, the diagnosis of gestation is important because the timing of gestation directly affects the running of farms. Various methods have been used to detect gestation, but none of them are ideal because of problems with the timing of detection or the accuracy, simplicity, or cost of the method. A new method for detecting gestation, which involves assessing interferon-tau (IFNT)-stimulated gene expression in peripheral blood leukocytes (PBL), was recently proposed. PBL fractionation methods were used to examine whether the expression profiles of various PBL populations could be used as reliable diagnostic markers of bovine gestation.

METHODS

PBL were collected on days 0 (just before artificial insemination), 7, 14, 17, 21, and 28 of gestation. The gene expression levels of the PBL were assessed with microarray analysis and/or quantitative real-time reverse transcription (q) PCR. PBL fractions were collected by flow cytometry or density gradient cell separation using Histopaque 1083 or Ficoll-Conray solutions. The expression levels of four IFNT-stimulated genes, interferon-stimulated protein 15 kDa (ISG15), myxovirus-resistance (MX) 1 and 2, and 2'-5'-oligoadenylate synthetase (OAS1), were then analyzed in each fraction through day 28 of gestation using qPCR.

RESULTS

Microarray analysis detected 72 and 28 genes in whole PBL that were significantly higher on days 14 and 21 of gestation, respectively, than on day 0. The upregulated genes included IFNT-stimulated genes. The expression levels of these genes increased with the progression of gestation until day 21. In flow cytometry experiments, on day 14 the expression levels of all of the genes were significantly higher in the granulocyte fraction than in the other fractions. Their expression gradually decreased through day 28 of gestation. Strong correlations were observed between the expression levels of the four genes in the granulocyte fractions obtained with flow cytometry and with density gradient separation.

CONCLUSIONS

The expression profiles of ISG15, MX1, MX2, and OAS1 could be a useful diagnostic biomarker of bovine gestation. Assessing the expression levels of these genes in a granulocyte fraction obtained with density gradient separation is a practical way of detecting gestation in cows within three weeks of insemination.

Transcriptomic analysis of the bovine endometrium: What is required to establish uterine receptivity to implantation in cattle?

In cattle, the majority of pregnancy loss can be attributed to early embryonic loss which occurs prior maternal recognition of pregnancy on Day 16 (Day 0 = ovulation). During this time, carefully orchestrated spatio-temporal alterations in the transcriptomic profile of the endometrium are required to drive conceptus elongation, via secretions from the endometrium (termed histotroph) and establish uterine receptivity to implantation. The two main modulators of these processed are progesterone (P4) and the pregnancy recognition signal interferon tau (IFNT). Altered concentrations of P4 in circulation mediate its effects via the endometrium and have been associated with different rates of conceptus elongation in cattle. Transcriptomic analysis of the endometrium has shown that modulation of circulating P4 alters endometrial expression of genes that can contribute to histotroph composition, which is beneficial (when P4 is supplemented) or detrimental (when P4 is reduced) to the developing conceptus. In addition, down-regulation of the progesterone receptor, required to establish uterine receptivity, is altered in the endometrium of heifers with altered P4 concentrations. IFNT, a type 1 interferon, also significantly impacts on the endometrial transcriptome. It induces the expression of a large number of classical interferon stimulated genes as early as Day 15 of pregnancy. In summary, the successful establishment of pregnancy in cattle requires a sequence of key events to ensure appropriate maternally derived secretions, establish uterine receptivity to implantation as well as an adequate endometrial response to IFNT production.

Evidence for an early endometrial response to pregnancy in cattle: both dependent upon and independent of interferon tau

The aims of this study were to 1) identify the earliest transcriptional response of the bovine endometrium to the presence of the conceptus (using RNAseq), 2) investigate if these genes are regulated by interferon tau (IFNT) in vivo, and 3) determine if they are predictive of the pregnancy status of postpartum dairy cows. RNAseq identified 459 differentially expressed genes (DEGs) between pregnant and cyclic endometria on day 16. Quantitative real-time PCR analysis of selected genes revealed PARP12, ZNFX1, HERC6, IFI16, RNF213, and DDX58 expression increased in pregnant compared with cyclic endometria on day 16 and were directly upregulated by intrauterine infusion of IFNT in vivo for 2 h ( P < 0.05). On day 13 following estrous endometrial expression of nine genes increased [ ARHGAP1, MGC127874, LIMS2, TBC1D1, FBXL7, C25H16orf71, LOC507810, ZSWIM4, and one novel gene (ENSBTAT00000050193)] and seven genes decreased ( SERBP1, SRGAP2, AL7A1, TBK1, F2RL2, MGC128929, and WBSCR17; P < 0.05) in pregnant compared with cyclic heifers. Of these DEGs, significant differences in expression between pregnant and cyclic endometria were maintained on day 16 for F2RL2, LIMS2, LOC507810, MGC127874, TBC1D1, WBSCR17, and ZSWIM4 ( P < 0.05) both their expression was not directly regulated by IFNT in vivo. Analysis of the expression of selected interferon-stimulated genes in blood samples from postpartum dairy cows revealed a significant increase ( P < 0.05) in expression of ZXFX1, PARP12, SAMD9, and HERC6 on day 18 following artificial insemination in cows subsequently confirmed pregnant compared with cyclic controls. In conclusion, RNAseq identified a number of novel pregnancy-associated genes in the endometrium of cattle during early pregnancy that are not regulated by IFNT in vivo. In addition, a number of genes that are directly regulated by short term exposure to IFNT in vivo are differentially expressed on day 18 following estrus detection in the blood of postpartum dairy cows depending on their pregnancy status.

Conceptus-endometrium crosstalk during maternal recognition of pregnancy in cattle

Successful growth and development of the posthatching blastocyst and pregnancy establishment are a result of the interaction between a competent embryo and a receptive uterine environment. We examined the global transcriptome profiles of the Day 16 bovine conceptus and pregnant endometrium tissues using RNA-Seq to identify genes that contribute to the dialogue during the period of pregnancy recognition. Using stringent filtering criterion, a total of 16 018 and 16 262 transcripts of conceptus and pregnant endometrium origin, respectively, were identified with distinct tissue-specific expression profiles. Of these, 2261 and 2505 transcripts were conceptus and endometrium specific. Using Cytoscape software, a total of 133 conceptus ligands that interact with corresponding receptors on the endometrium and 121 endometrium ligands that interact with corresponding receptors on the conceptus were identified. While 87 ligands were commonly detected, 46 were conceptus specific and 34 endometrium specific. This study is one of the first to provide a comprehensive list of potentially secreted molecules in the conceptus that interact with receptors on the endometrium and vice versa during the critical window of maternal recognition of pregnancy. The identified tissue-specific genes may serve as candidates to study pregnancy recognition and they or downstream products may represent potential early markers of pregnancy.

Pregnancy recognition and abnormal offspring syndrome in cattle

Development of the post-hatching conceptus in ruminants involves a period of morphological expansion that is driven by complex interactions between the conceptus and its intrauterine environment. As a result of these interactions, endometrial physiology is altered, leading to establishment of the pregnancy and continued development of the placenta. Disruption of normal fetal and placental development can occur when embryos are exposed to manipulations in vitro or when inappropriate endocrine sequencing occurs in vivo during the pre- and peri-implantation periods. The present review addresses the development of the post-hatching bovine conceptus, its interactions with the maternal system and changes in development that can occur as a result of in vivo and in vitro manipulations of the bovine embryo.

Differential expression of the type I interferon pathway during persistent and transient bovine viral diarrhea virus infection

Persistent infection with bovine viral diarrhea virus (BVDV) serves as a reservoir for the perpetuation of infection in cattle populations and causes a range of adverse effects on the health of the host. To study the interactions of the virus with the host, gene expression was compared in the blood of persistently infected (PI) and uninfected steer, and in the blood and tissues of PI fetuses, transiently infected (TI), and uninfected bovine fetuses. Microarray analysis of PI steer blood revealed differential gene expression indicative of an interferon (IFN) response including genes involved in cell cycle regulation, which may contribute to long-term adverse effects. Upregulation of IFN-stimulated genes (e.g., ISG15, PKR) and RNA helicases (RIG-I, LGP2, MDA-5) was identified in both PI fetal and steer blood in comparison to controls, indicating a continued stimulation of the innate antiviral response as a result of the persistent viremia. ISG15 was studied in further detail, implicating reticular cells as basal producers of ISG15 in the spleen, in addition to endothelial and macrophage-like cells in infected spleen. Consequences of chronic IFN pathway activation in PI cattle may include growth- and immunosuppression, the pathogenesis of which is still poorly understood. This study lends new insights into the interactions between BVDV and its host, and can serve as a model for studies of the role of the IFN system in persistent infections.

Genes involved in conceptus–endometrial interactions in ruminants: insights from reductionism and thoughts on holistic approaches

This review summarizes new knowledge on expression of genes and provides insights into approaches for study of conceptus–endometrial interactions in ruminants with emphasis on the peri-implantation stage of pregnancy. Conceptus–endometrial interactions in ruminants are complex and involve carefully orchestrated temporal and spatial alterations in gene expression regulated by hormones from the ovary and conceptus. Progesterone is the hormone of pregnancy and acts on the uterus to stimulate blastocyst survival, growth, and development. Inadequate progesterone levels or a delayed rise in progesterone is associated with pregnancy loss. The mononuclear trophectoderm cells of the elongating blastocyst synthesize and secrete interferon-τ (IFNT), the pregnancy recognition signal. Trophoblast giant binucleate cells begin to differentiate and produce hormones including chorionic somatomammotropin 1 (CSH1 or placental lactogen). A number of genes, induced or stimulated by progesterone, IFNT, and/or CSH1 in a cell-specific manner, are implicated in trophectoderm adhesion to the endometrial luminal epithelium and regulation of conceptus growth and differentiation. Transcriptional profiling experiments are beginning to unravel the complex dynamics of conceptus–endometrial interactions in cattle and sheep. Future experiments should incorporate physiological models of pregnancy loss and be complemented by metabolomic studies of uterine lumen contents to more completely define factors required for blastocyst survival, growth, and implantation. Both reduction and holistic approaches will be important to understand the multifactorial phenomenon of recurrent pregnancy loss and provide a basis for new strategies to improve pregnancy outcome and reproductive efficiency in cattle and other domestic animals.

The hinge region between two ubiquitin-like domains destabilizes recombinant ISG15 in solution

Interferon-stimulated gene (ISG) 15 mediates antiviral responses and also is upregulated within the endometrium in response to the developing embryo during early pregnancy. Structurally, ISG15 resembles two ubiquitin domains (30% identical) that are separated by a hinge region. Recombinant (r) bovISG15 is not stable in solution. It was hypothesized that the hinge region contributed to the instability of rbovISG15. Within 24 h of dialysis, rbovISG15 formed complexes as detected by reducing and denaturing SDS-PAGE. However, chemical perturbations of cysteine prevented formation of rbovISG15 complexes over time. Furthermore, a site-directed mutant of rbovISG15 (Cys80Ser) was isomeric and more stable than rbovISG15. Neither wild-type nor mutant rbovISG15 was able to interact with the ISG15 E1 initiating enzyme, UBE1L, in an in vitro pull-down assay. Ovine (ov) ISG15 has three additional amino acids within the hinge region that were hypothesized to increase stability and the degree of interaction with UBE1L because of increased separation of the ubiquitin-like domains. Over time in solution, rovISG15 the level of rovISG15 secondary structure was diminished, whereas the Cys80Ser rovISG15 structure did not change. A GST-Cys80Ser rovISG15 fusion protein had increased structural stability and enhanced protein-protein interaction with UBE1L after dialysis for 48 h, when compared to the GST-rovISG15 fusion protein or rbovISG15. Models of bovISG15, Cys80Ser bovISG15, and ovISG15 were constructed, which confirmed that the hinge region between the two ubiquitin domains destabilizes rbovISG15 in solution.

A ubiquitin E3 ligase Efp is up-regulated by interferons and conjugated with ISG15

Interferon (IFN) regulates various target genes that mediate important roles in immune responses such as antiviral state. Protein ISG15-conjugation (ISGylation) is implicated in the IFN-induced antiviral response. Here we demonstrate that Efp mRNA as well as protein expression could be up-regulated by Type I IFN in HeLa cells and HepG2 cells. Luciferase assay reveals that the first intron of Efp gene contains a functional interferon-stimulated response element (ISRE) and electrophoretic mobility shift assay shows that the ISRE binds to signal transducer and activator of transcription 1 (STAT1). Chromatin immunoprecipitation assays have shown that the ISRE recruits STAT1 in vivo IFN-dependently. Moreover, we demonstrate that Efp protein could be conjugated with not only ubiquitin but also ISG15. These data suggest that Efp is an IFN-responsive gene that potentially mediates IFN actions, involved in ISGylation and ubiquitination of proteins including Efp itself.

Embryo-induced transcriptome changes in bovine endometrium reveal species-specific and common molecular markers of uterine receptivity

The endometrium plays a central role among the reproductive tissues in the context of early embryo–maternal communication and pregnancy. This study investigated transcriptome profiles of endometrium samples from day 18 pregnant vs non-pregnant heifers to get insight into the molecular mechanisms involved in conditioning the endometrium for embryo attachment and implantation. Using a combination of subtracted cDNA libraries and cDNA array hybridisation, 109 mRNAs with at least twofold higher abundance in endometrium of pregnant animals and 70 mRNAs with higher levels in the control group were identified. Among the mRNAs with higher abundance in pregnant animals, at least 41 are already described as induced by interferons. In addition, transcript levels of many new candidate genes involved in the regulation of transcription, cell adhesion, modulation of the maternal immune system and endometrial remodelling were found to be increased. The different expression level was confirmed with real-time PCR for nine genes. Localisation of mRNA expression in the endometrium was shown byin situhybridisation forAGRN,LGALS3BP,LGALS9,USP18,PARP12andBST2. A comparison with similar studies in humans, mice, and revealed species-specific and common molecular markers of uterine receptivity.

Monozygotic Twin Model Reveals Novel Embryo-Induced Transcriptome Changes of Bovine Endometrium in the Preattachment Period1

Initiation and maintenance of pregnancy are critically dependent on an intact embryo-maternal communication in the preimplantation period. To get new insights into molecular mechanisms underlying this complex dialog, a holistic transcriptome study of endometrium samples from Day 18 pregnant vs. nonpregnant twin cows was performed. This genetically defined model system facilitated the identification of specific conceptus-induced changes of the endometrium transcriptome. Using a combination of subtracted cDNA libraries and cDNA array hybridization, 87 different genes were identified as upregulated in pregnant animals. Almost one half of these genes are known to be stimulated by type I interferons. For the ISG15ylation system, which is assumed to play an important role in interferon tau (IFNT) signaling, mRNAs of four potential components (IFITM1, IFITM3, HSXIAPAF1, and DTX3L) were found at increased levels in addition to ISG15 and UBE1L. These results were further substantiated by colocalization of these mRNAs in the endometrium of pregnant animals shown by in situ hybridization. A functional classification of the identified genes revealed several different biological processes involved in the preparation of the endometrium for the attachment and implantation of the embryo. Specifically, elevated transcript levels were found for genes involved in modulation of the maternal immune system, genes relevant for cell adhesion, and for remodeling of the endometrium. This first systematic study of maternal transcriptome changes in response to the presence of an embryo on Day 18 of pregnancy in cattle is an important step toward deciphering the embryo-maternal dialog using a systems biology approach.