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

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.

Novel aspects of endometrial function: a biological sensor of embryo quality and driver of pregnancy success

Successful pregnancy depends on complex biological processes that are regulated temporally and spatially throughout gestation. The molecular basis of these processes have been examined in relation to gamete quality, early blastocyst development and placental function, and data have been generated showing perturbations of these developmental stages by environmental insults or embryo biotechnologies. The developmental period falling between the entry of the blastocyst into the uterine cavity to implantation has also been examined in terms of the biological function of the endometrium. Indeed several mechanisms underlying uterine receptivity, controlled by maternal factors, and the maternal recognition of pregnancy, requiring conceptus-produced signals, have been clarified. Nevertheless, recent data based on experimental perturbations have unveiled unexpected biological properties of the endometrium (sensor/driver) that make this tissue a dynamic and reactive entity. Persistent or transient modifications in organisation and functionality of the endometrium can dramatically affect pre-implantation embryo trajectory through epigenetic alterations with lasting consequences on later stages of pregnancy, including placentation, fetal development, pregnancy outcome and post-natal health. Developing diagnostic and prognostic tools based on endometrial factors may enable the assessment of maternal reproductive capacity and/or the developmental potential of the embryo, particularly when assisted reproductive technologies are applied.

Transcriptomic changes in the bovine conceptus between the blastocyst stage and initiation of implantation

Conceptus-maternal communication is vital for the successful establishment and maintenance of pregnancy, yet relatively little information exists for many of the mechanisms and the nature of the conceptus signals responsible for this cross-talk. Sub-optimal communication, resulting from impairment of conceptus development and/or from abnormal uterine receptivity, contributes to a high incidence of embryonic mortality. Therefore, detailed examination of the mechanisms regulating both pre- and peri-implantation conceptus development are necessary to fully understand the factors regulating successful post-hatching development, pregnancy recognition and implantation signaling. Despite significant progress in understanding of the temporal changes in the transcriptome of the uterine endometrium, there is only a rudimentary knowledge of the genes and pathways governing growth and development of the cattle conceptus. Furthermore, although there are a large number of studies describing gene expression profiles in bovine embryos focused mainly during the earlier preimplantation stages (up to and including Day 7), very little information exists for the post-hatching embryo and elongating conceptus. This period of development is arguably more important as a significant proportion of all embryonic loss occurs between Days 8 and 16 of pregnancy in cattle, corresponding to the time of hatching of the blastocyst from the zona pellucida and its subsequent elongation coincident with the time of maternal recognition of pregnancy. Given that this is a critical period in development leading up to maternal recognition and establishment of pregnancy, the identification of key genes and pathways regulating these crucial developmental events is essential.

Transcriptome analyses of bovine, porcine and equine endometrium during the pre-implantation phase

Different reproductive strategies evolved in various mammalian groups to achieve recognition, establishment and maintenance of pregnancy. The complexity of these processes is reflected by a high incidence of embryonic loss during this critical period in many mammalian species. Besides studies in mice and humans a number of transcriptome studies of endometrial tissue samples and also of early embryos have been performed during the pre-implantation phase in cattle, swine and horse to identify genes associated with embryo-maternal interaction. Results of these studies are reviewed and compared between species. The comparison of data sets from different species indicated a general role of interferons for the establishment of pregnancy. In addition to many species-specific changes in gene expression, which may reflect different pregnancy recognition signals and mechanisms of embryo implantation, a number of transcriptome changes were found to be similar across species. These genes may have conserved roles during the establishment of pregnancy in mammals and reflect basic principles of mammalian reproduction. The relevance and strategies, but also the challenges of cross-species comparisons of gene expression data are discussed.

Oviductal, endometrial and embryonic gene expression patterns as molecular clues for pregnancy establishment

In higher animals, the beginning of new life and transfer of genetic material to the next generation occurs in the oviduct when two distinct gametes cells unite resulting in the formation of a zygote. The zygote then undergoes serial developmental processes in the oviduct and enters into the uterus where it faces challenges and scrutiny from the endometrial ecosystem. Thus, embryos that are able to establish an appropriate embryo-maternal dialogue are capable of developing to term whereas the incompetent ones can perish any time during the gestation period. Although several lines of evidences indicated that pregnancy loss is a multi-factorial phenomenon, the biochemical composition of the embryo and maternal environment are the main players to determine pregnancy outcome. Indeed, expression patterns of the genes are the driving forces that induce biochemical composition changes in embryo, oviduct and uterine environment. Thus, examining the molecular signals that are associated with oviductal or endometrial receptivity and embryo implantation is essential for establishing strategies to improve pregnancy success. Therefore, this review focuses on the contribution of oviduct and its transcriptome profile on early stage embryo development and the impact of endometrium and its transcriptome changes on peri and post embryo implantation. In addition, this paper integrates established facts about hormonal and molecular signatures associated with endometrial receptivity. Finally, the blastocyst and pre-conception endometrial gene expression profiles have been discussed in relation to the pregnancy outcome to highlight the potentials of blastocyst and pre-transfer endometrial transcriptome profile approach for selecting appropriate recipient and developmentally competent embryo.

Effects of lactation and pregnancy on gene expression of endometrium of Holstein cows at day 17 of the estrous cycle or pregnancy

Objectives were to determine effects of lactation and pregnancy on endometrial gene expression on d 17 of the estrous cycle and pregnancy. Heifers (n = 33) were assigned randomly after parturition to lactating (L, n = 17) or nonlactating (NL, n = 16) groups. Cows were subjected to an ovulation synchronization program for a timed artificial insemination (TAI); 10 cows in L and 12 in NL were inseminated. Slaughter occurred 17 d after the day equivalent to TAI, and intercaruncular endometrial tissues were collected. Gene expression was determined by DNA microarray analysis for pregnant (L, n = 8; NL, n = 6) and noninseminated cyclic (L, n = 7; NL, n = 4) cows. Differentially expressed genes were selected with a P-value <0.01 and absolute expression >40. In addition, a fold effect >1.5 was used as a criterion for genes affected by pregnancy. In total, 210 genes were differentially regulated by lactation (136 downregulated and 74 upregulated), and 702 genes were differentially regulated by pregnancy (407 downregulated and 295 upregulated). The interaction effect of pregnancy and lactation affected 61 genes. Genes up- and downregulated in pregnant cows were associated with several gene ontology terms, such as defense response and interferon regulatory factor, cell adhesion, and extracellular matrix. The gene ontology analyses of up- and downregulated genes of lactating cows revealed terms related to immunoglobulin-like fold, immune response, COMM domain, and non-membrane-bounded organelle. Several genes upregulated by lactation, such as IGHG1, IGLL1, IGK, and TRD, were related to immune function, particularly for B cells and γδ T cells. Developmental genes related to limb and neural development and glucose homeostasis (e.g., DKK1, RELN, PDK4) were downregulated by lactation, whereas an interaction was also detected for RELN. The stated genes associated with immune function and developmental genes expressed in the endometrium affected by lactational state are possible candidate genes for interventions to improve fertility of lactating dairy cows.

Effects of lactation and pregnancy on metabolic and hormonal responses and expression of selected conceptus and endometrial genes of Holstein dairy cattle

Objectives were to characterize postpartum metabolic and hormonal differences between nonlactating and lactating dairy cows, evaluate lactation and pregnancy effects on endometrium and conceptus expression of selected genes, and characterize associations between conceptus and endometrial expression of genes in early pregnancy (d 17). Pregnant heifers were assigned randomly after calving to a lactating group (L, n=17) and a nonlactating group (NL, n=16). The L cows were fed a total mixed ration [1.65 Mcal of net energy for lactation (NE(L))/kg, 16.5% crude protein (CP)] ad libitum, and the NL cows were fed a maintenance ration (1.45 Mcal of NE(L)/kg, 12.2% CP) once per day. All cows were presynchronized and enrolled in a timed artificial insemination (TAI) protocol; 10 cows in the L and 12 in the NL received TAI. On d 17 after GnRH and TAI, cows were slaughtered and endometrial and conceptus tissues collected. The Affymetrix Bovine Genome DNA Microarray (Affymetrix Inc., Santa Clara, CA) was used to assess conceptus and endometrial gene expression. The L cows had higher body temperature than the NL cows (38.4 vs. 38.2°C), and the NL cows cycled earlier than the L cows (26.3 vs. 34.7 d in milk). Cows in the L group had greater plasma concentrations of β-hydroxybutyrate (4.90 vs. 2.97 mg/dL) and blood urea N (11.6 vs. 6.5mg/dL) and lower concentrations of glucose (74.0 vs. 79.9 mg/dL) compared with NL cows. Insulin-like growth factor-1 was lower for L compared with NL (140.5 vs. 198.2 ng/mL) and was greater for cows subsequently classified pregnant compared with cyclic (191.0 vs. 147.6 ng/mL). The concentration of progesterone from GnRH or TAI (d 0) until d 17 was lower for L cows than for NL cows. Gene expression analyses indicated that all conceptuses (n=13) expressed pregnancy-associated glycoprotein (PAG) genes PAG2, PAG8, PAG11, and PAG12. The same PAG family genes were observed in the endometrium of some pregnant cows. Simple and standard partial correlation analyses detected associations of conceptus PAG11 with prostaglandin regulatory genes. In conclusion, lactation altered metabolic status, delayed initiation of cyclicity, and decreased concentrations of progesterone in pregnant cows. Early expression of PAG genes in the conceptus may contribute to successful development of early pregnancy and possibly alter mechanisms related with embryo survival such as prostaglandin synthesis.

Influence of progesterone on oocyte quality and embryo development in cows

In cattle, the majority of embryo loss occurs very early during pregnancy (approximately Day 16), around or prior to maternal recognition of pregnancy. The actions of P4 in controlling LH pulsatility and ovarian follicular development may impinge negatively on oocyte quality. A considerable proportion of embryo loss may be attributable to inadequate circulating progesterone (P4) concentrations and the subsequent downstream consequences on endometrial gene expression and histotroph secretion into the uterine lumen. Conceptus growth and development require the action of P4 on the uterus to regulate endometrial function, including conceptus-maternal interactions, pregnancy recognition, and uterine receptivity for implantation. This review summarizes recent data highlighting the role of progesterone in determining oocyte quality and embryo development in cattle.

Embryo-maternal communication: signalling before and during placentation in cattle and pig

Communication during early pregnancy is essential for successful reproduction. In this review we address the beginning of the communication between mother and developing embryo; including morphological and transcriptional changes in the endometrium as well as epigenetic regulation mechanisms directing the placentation. An increasing knowledge of the embryo-maternal communication might not only help to improve the fertility of our farm animals but also our understanding of human health and reproduction.

Early developing pig embryos mediate their own environment in the maternal tract

The maternal tract plays a critical role in the success of early embryonic development providing an optimal environment for establishment and maintenance of pregnancy. Preparation of this environment requires an intimate dialogue between the embryo and her mother. However, many intriguing aspects remain unknown in this unique communication system. To advance our understanding of the process by which a blastocyst is accepted by the endometrium and better address the clinical challenges of infertility and pregnancy failure, it is imperative to decipher this complex molecular dialogue. The objective of the present work is to define the local response of the maternal tract towards the embryo during the earliest stages of pregnancy. We used a novel in vivo experimental model that eliminated genetic variability and individual differences, followed by Affymetrix microarray to identify the signals involved in this embryo-maternal dialogue. Using laparoscopic insemination one oviduct of a sow was inseminated with spermatozoa and the contralateral oviduct was injected with diluent. This model allowed us to obtain samples from the oviduct and the tip of the uterine horn containing either embryos or oocytes from the same sow. Microarray analysis showed that most of the transcripts differentially expressed were down-regulated in the uterine horn in response to blastocysts when compared to oocytes. Many of the transcripts altered in response to the embryo in the uterine horn were related to the immune system. We used an in silico mathematical model to demonstrate the role of the embryo as a modulator of the immune system. This model revealed that relatively modest changes induced by the presence of the embryo could modulate the maternal immune response. These findings suggested that the presence of the embryo might regulate the immune system in the maternal tract to allow the refractory uterus to tolerate the embryo and support its development.

Proteome of the early embryo-maternal dialogue in the cattle uterus

We analyzed embryo-maternal interactions in the bovine uterus on day 8 of development. Proteomic profiles were obtained by two-dimensional difference gel electrophoresis from 8 paired samples of uterine fluid (UF) from the same animal with and without embryos in the uterus. Results were contrasted with UF obtained after artificial insemination. We detected 50 differential protein spots (t test, p < 0.05). Subsequent protein characterization by nano-LC-ESI-MS/MS enabled us to identify 38 proteins, obtaining for first time the earliest evidence of involvement of the down-regulated NFkB system in cattle as a pregnancy signature pathway. Embryos enhanced the embryotrophic ability of UF and decreased uterine protein, while blood progesterone was unaltered. Twinfilin, hepatoma-derived growth factor, and synaptotagmin-binding cytoplasmic RNA interacting protein have not previously been identified in the mammalian uterus. TNFα and IL-1B were localized to embryos by immunocytochemistry, and other proteins were validated by Western blot in UF. Glycosylated-TNFα, IL-1B, insulin, lactotransferrin, nonphosphorylated-peroxiredoxin, albumin, purine nucleoside phosphorylase, HSPA5, and NFkB were down-regulated, while phosphorylated-peroxiredoxin, annexin A4, and nonglycosylated-TNFα were up-regulated. The embryonic signaling agents involved could be TNFα and IL-1B, either alone or in a collective dialogue with other proteins. Such molecules might explain the immune privilege during early bovine development.

Functions of interferon tau as an immunological regulator for establishment of pregnancy

The establishment of a successful pregnancy requires a "fine quality embryo", "maternal recognition of pregnancy", and a "receptive uterus" during the period of conceptus implantation to the uterine endometrium. In ruminants, a conceptus cytokine, interferon tau (IFNT), a major cytokine produced by the peri-implantation trophectoderm, is known as a key factor for maternal recognition of pregnancy. IFNT can be considered one of the main factors in conceptus-uterus cross-talk, resulting in the rescue of ovarian corpus luteum (CL), induction of endometrial gene expressions, activation of residual immune cells, and recruitment of immune cells. Much research on IFNT has focused on the CL life-span (pregnancy recognition) and uterine gene expression through IFNT and related genes; however, immunological acceptance of the conceptus by the mother has not been well characterized. In this review, we will discuss the progress in IFNT and implantation research made by us and others for over 10 years, and relate this progress to pregnancy in mammalian species other than ruminants.

Exploring the application of high-throughput genomics technologies in the field of maternal-embryo communication

Deciphering the complex molecular dialogue between the maternal tract and embryo is crucial to increasing our understanding of pregnancy failure, infertility problems and in the modulation of embryo development, which has consequences through adulthood. High-throughput genomic technologies have been applied to look for a holistic view of the molecular interactions occurring during this dialogue. Among these technologies, microarrays have been widely used, being one of the most popular tools in maternal-embryo communication. Today, next generation sequencing technologies are dwarfing the capabilities of microarrays. The application of these new technologies has broadened to almost all areas of genomics research, because of their massive sequencing capacity. We review the current status of high-throughput genomic technologies and their application to maternal-embryo communication research. We also survey next generation technologies and their huge potential in many research areas. Given the diversity of unanswered questions in the field of maternal-embryo communication and the wide range of possibilities that these technologies offer, here we discuss future perspectives on the use of these technologies to enhance maternal-embryo research.

Is DNA methylation an epigenetic contribution to transcriptional regulation of the bovine endometrium during the estrous cycle and early pregnancy?

Epigenetic events controlling the transcriptional regulation of genes involved in endometrial function during the estrous cycle and early pregnancy have only sparsely been investigated. We analyzed the gene expression of DNA methyltransferases and the most prominent endocrine transcriptional mediator estrogen receptor alpha (ESR1) in the bovine endometrium of heifers at 0, 12 and 18 days following estrous and at day 18 after insemination. The luminometric methylation assay for the investigation of global DNA methylation and an elegant combination of methylation-sensitive high resolution melting and pyrosequencing for local methylation levels of ESR1 were deployed. In spite of differential gene expression of ESR1 among groups, no differences in endometrial ESR1 DNA methylation during neither estrous cycle nor early pregnancy were determined. Global DNA methylation prevailed at similar low levels in endometrium, likely controlled by the observed moderate DNMT3b expression. Thus, the epigenetic contribution of DNA methylation influencing endometrial function seems rather limited. However, because a control tissue expressing only minute amounts of ESR1 transcripts was locally significantly higher methylated, DNA methylation might contribute to an appropriate tissue-specific expression status underlying further specific control mechanisms of gene transcription.

Effects of human chorionic gonadotrophin administration on Day 5 after oestrus on corpus luteum characteristics, circulating progesterone and conceptus elongation in cattle

The aim of the present study was to test the hypothesis that elevated concentrations of progesterone (P4) resulting from the induction of an accessory corpus luteum (CL) by human chorionic gonadotrophin (hCG) administration on Day 5 after oestrus would lead to advanced conceptus elongation on Day 14 following embryo transfer on Day 7. The oestrous cycles of cross-bred beef heifers were synchronised and animals were randomly assigned to receive either of two treatments: (1) intramuscular injection of 3000 IU hCG on Day 5 after oestrus (n = 14); or (2) intramuscular injection of saline on Day 5 after oestrus (n = 13). Ovaries were scanned daily by transrectal ultrasonography to assess CL development. Serum concentrations of P4 were determined from daily blood samples collected from the jugular vein. In vitro-produced bovine blastocysts were transferred to synchronised recipients on Day 7 after oestrus (n = 15 blastocysts per recipient). Heifers were killed on Day 14 after oestrus and the uterus was flushed to recover the embryos. Injection of hCG on Day 5 induced ovulation of the dominant follicle in all treated heifers and increased the total area of luteal tissue on the ovary, which was associated with a significant increase (P < 0.001) in serum concentrations of P4 from Day 7 to Day 14. Positive associations were detected between circulating P4 with CL area (within-day correlations ranging from r = 0.45 to r = 0.67) and total area of luteal tissue (within-day correlations ranging from r = 0.65 to r = 0.86) Administration of hCG did not affect the proportion of Day 14 conceptuses recovered. However, compared with the control group, hCG-treated heifers had increased conceptus length (3.91 ± 1.23 vs 5.57 ± 1.02 mm, respectively; P = 0.06), width (1.00 ± 0.06 vs 1.45 ± 0.05 mm, respectively; P = 0.002) and area (5.71 ± 0.97 vs 8.31 ± 0.83, respectively; P = 0.02). Although numerically greater, mean interferon-τ (IFNT) production in vitro did not differ significantly (P = 0.54) between embryos recovered from hCG-treated and control heifers. In contrast, there was a strong positive correlation between individual embryo length (r = 0.76; P < 0.001) and individual embryo area (r = 0.72; P < 0.001) and IFNT production. In conclusion, administration of hCG on Day 5 after oestrus resulted in the formation of an accessory CL and hypertrophy of the original CL, the result of which was an increase in P4 concentrations from Day 7 onwards. These elevated P4 concentrations were associated with an increased conceptus area. Furthermore, conceptus size was highly correlated with IFNT secretion in vitro.

Endometrial gene expression during early pregnancy differs between fertile and subfertile dairy cow strains

A receptive uterine environment is a key component in determining a successful reproductive outcome. We tested the hypothesis that endometrial gene expression patterns differ in fertile and subfertile dairy cow strains. Twelve lactating dairy cattle of strains characterized as having fertile (n = 6) and subfertile (n = 6) phenotypes underwent embryo transfer on day 7 of the reproductive cycle. Caruncular and intercaruncular endometrial tissue was obtained at day 17 of pregnancy, and microarrays used to characterize transcriptional profiles. Statistical analysis of microarray data at day 17 of pregnancy revealed 482 and 1,021 differentially expressed transcripts (P value < 0.05) between fertile and subfertile dairy cow strains in intercaruncular and caruncular tissue, respectively. Functional analysis revealed enrichment for several pathways involved in key reproductive processes, including the immune response to pregnancy, luteolysis, and support of embryo growth and development, and in particular, regulation of histotroph composition. Genes implicated in the process of immune tolerance to the embryo were downregulated in subfertile cows, as were genes involved in preventing luteolysis and genes that promote embryo growth and development. This study provides strong evidence that the endometrial gene expression profile may contribute to the inferior reproductive performance of the subfertile dairy cow strain.

Identification of RNF213 as a susceptibility gene for moyamoya disease and its possible role in vascular development

Background

Moyamoya disease is an idiopathic vascular disorder of intracranial arteries. Its susceptibility locus has been mapped to 17q25.3 in Japanese families, but the susceptibility gene is unknown.

Methodology/Principal Findings

Genome-wide linkage analysis in eight three-generation families with moyamoya disease revealed linkage to 17q25.3 (P<10^-4). Fine mapping demonstrated a 1.5-Mb disease locus bounded by D17S1806 and rs2280147. We conducted exome analysis of the eight index cases in these families, with results filtered through Ng criteria. There was a variant of p.N321S in PCMTD1 and p.R4810K in RNF213 in the 1.5-Mb locus of the eight index cases. The p.N321S variant in PCMTD1 could not be confirmed by the Sanger method. Sequencing RNF213 in 42 index cases confirmed p.R4810K and revealed it to be the only unregistered variant. Genotyping 39 SNPs around RNF213 revealed a founder haplotype transmitted in 42 families. Sequencing the 260-kb region covering the founder haplotype in one index case did not show any coding variants except p.R4810K. A case-control study demonstrated strong association of p.R4810K with moyamoya disease in East Asian populations (251 cases and 707 controls) with an odds ratio of 111.8 (P = 10⁻¹¹⁹). Sequencing of RNF213 in East Asian cases revealed additional novel variants: p.D4863N, p.E4950D, p.A5021V, p.D5160E, and p.E5176G. Among Caucasian cases, variants p.N3962D, p.D4013N, p.R4062Q and p.P4608S were identified. RNF213 encodes a 591-kDa cytosolic protein that possesses two functional domains: a Walker motif and a RING finger domain. These exhibit ATPase and ubiquitin ligase activities. Although the mutant alleles (p.R4810K or p.D4013N in the RING domain) did not affect transcription levels or ubiquitination activity, knockdown of RNF213 in zebrafish caused irregular wall formation in trunk arteries and abnormal sprouting vessels.

Conclusions/Significance

We provide evidence suggesting, for the first time, the involvement of RNF213 in genetic susceptibility to moyamoya disease.

Endometrial expression of progesterone-induced blocking factor and galectins-1, -3, -9, and -3 binding protein in the luteal phase and early pregnancy in cattle

Progesterone-induced blocking factor (PIBF) and galectins modulate the maternal immune response during pregnancy. We hypothesized that the relative transcript abundance of the above genes would be different during the luteal phase/early pregnancy and would be affected by progesterone supplementation. To further test this, hypothesis protein expression analyses were carried out to evaluate the abundance and localization of LGALS9 and PIBF. Following estrus synchronization, heifers were inseminated ( n = 140) or not ( n = 70). Half the heifers in each status (cyclic or potentially pregnant) were randomly assigned to receive a progesterone-releasing intravaginal device (PRID) on day 3 after estrus, which elevated progesterone concentrations from day 3.5 to 8 ( P < 0.05), resulting in four treatment groups: cyclic and pregnant heifers, each with normal and high progesterone. After confirmation of pregnancy status in inseminated animals, uterine tissue was collected on days 5, 7, 13, or 16 of the luteal phase of the cycle/pregnancy. Gene and protein expression was determined using Q-RT-PCR and IHC, respectively, on 5 heifers per treatment per time point (i.e., 80 in total). Progesterone concentrations did not affect expression of any of the genes ( P > 0.05). LGALS9 and LGALS3BP were expressed at low levels in both cyclic and pregnant endometria until day 13. On day 16, expression increased only in the pregnant heifers ( P < 0.0001). LGALS1 and LGALS3 decreased on day 7 ( P < 0.0001) and remained low until day 16. Pregnancy had no effect on the expression of LGALS1, LGALS3, and PIBF. Additionally, LGALS9 and PIBF proteins were expressed in distinct uterine cell types. These results indicate that the galectins may be involved in uterine receptivity and/or implantation in heifers.

Transcriptome changes at the initiation of elongation in the bovine conceptus

The majority of embryonic loss in cattle occurs before maternal recognition of pregnancy, at around Day 16 postconception. The origin of the embryo can have a significant impact on the dynamics of embryo mortality. The aim of this study was to examine the temporal changes in transcriptional profile as the embryo develops from a spherical blastocyst on Day 7 to an ovoid conceptus at the initiation of elongation on Day 13 and to highlight differences in these temporal gene expression dynamics between in vivo- and in vitro-derived blastocysts that may be associated with embryonic survival/mortality using the bovine Affymetrix microarray. All embryos were produced either in vitro by in vitro fertilization or in vivo by superovulation. A proportion of Day 7 blastocysts were snap frozen, and the remainder were transferred (n = 10 per recipient) to synchronized heifers, recovered on Day 13, and snap frozen individually. Three pools of Day 7 blastocysts (n = 25 per pool) and Day 13 conceptuses (n = 5 per pool) were used for microarray analysis. In Day 7 blastocysts, 50 genes were found to be differentially expressed (P < 0.05), of which 19 were up-regulated and 31 down-regulated in the in vivo compared to in vitro embryos. In Day 13 conceptuses, 288 genes were found to be differentially expressed (P < 0.05), of which 133 were up-regulated and 155 down-regulated in the in vivo compared to in vitro embryos. The comparison between Day 7 and Day 13 embryos revealed significant temporal changes in transcript profile with 1806 and 909 transcripts differentially expressed in the in vitro- and in vivo-derived embryos, respectively. Across the three array comparisons between Day 7 and Day 13 embryos, 444 genes were consistently exclusively present in the in vivo embryos, whereas 1341 were exclusively present in the in vitro embryos. Regardless of the origin of the embryo, 465 differentially expressed genes between Day 7 and 13 were common to both in vivo- and in vitro-derived embryos; these genes are likely critical for the transition between the blastocyst (Day 7) and ovoid conceptus (Day 13) stages of embryo development. In order to validate the microarray findings, differences in the expression of six genes (CYP51A1, FADS1, TDGF1, HABP2, APOA2, and SLC12A2) were confirmed by quantitative real-time PCR on in vivo- and in vitro-derived embryos on Day 7 and Day 13 using independent samples from those used for the microarray. Subsequent mapping of these differentially expressed genes into relevant functional groups and pathways identified important pathways involved in conceptus elongation in cattle. In conclusion, this analysis has identified genes and pathways crucial for the transition from a spherical blastocyst to an ovoid conceptus as well as those uniquely associated with a greater likelihood of embryonic survival (those unique to in vivo embryos) or loss (those unique to in vitro embryos).

Bovine endometrial metallopeptidases MMP14 and MMP2 and the metallopeptidase inhibitor TIMP2 participate in maternal preparation of pregnancy

Early embryonic development is critically dependent on both maternal preparation and embryonic signalling of pregnancy. Matrix metallopeptidases (MMP) contribute to spatial and temporal matrix remodeling in the bovine endometrium. In this study we observed distinct changes in expression of MMP2, MMP14, and the metallopeptidase inhibitor TIMP2 between different phases of the estrous cycle indicating an endocrine regulation. An increase of TIMP2 protein abundance was ascertained in the uterine lumen during the time of embryo elongation. The expression pattern and cellular localization correlate well with the assumed effects of MMPs on release and activation of cytokines and growth factors directing cell migration, differentiation, and vascularization during this pivotal period of development. Specifically, active MMP2 in the endometrium may determine the allocation of growth factors supporting conceptus development. The presence of a day 18 conceptus in vivo and day 8 blastoysts in vitro induced endometrial TIMP2 mRNA expression. The results imply that TIMP2 is involved in very early local maternal recognition of pregnancy. Matrix metallopeptidases are likely to participate in remodeling processes preparing a receptive endometrium for a timely and precise regulation of embryo development.

Dynamic proteome signatures in gametes, embryos and their maternal environment

Comprehensive molecular analysis at the level of proteins represents a technically demanding, but indispensable, task since several post-transcriptional regulation mechanisms disable a valid prediction of quantitative protein expression profiles from transcriptome analysis. In crucial steps of gamete and early embryo development, de novo transcription is silenced, meaning that almost all macromolecular events take place at the level of proteins. In this review, we describe selected examples of dynamic proteome signatures addressing capacitation of spermatozoa, in vitro maturation of oocytes, effect of oestrous cycle on oviduct epithelial cells and embryo-induced alterations to the maternal environment. We also present details of the experimental strategies applied and the experiments performed to verify quantitative proteomic data. Far from being comprehensive, examples were selected to cover several mammalian species as well as the most powerful proteomic techniques currently applied. To enable non-experts in the field of proteomics to appraise published proteomic data, our examples are preceded by a customised description of quantitative proteomic methods, covering 2D difference gel electrophoresis (2D-DIGE), nano-liquid chromatography combined with tandem mass spectrometry, and label-free as well as stable-isotope labelling strategies for mass spectrometry-based quantifications.

Immunological mechanisms to establish embryo tolerance in early bovine pregnancy

A well-balanced immunological interaction between mother and the semi-allogenic embryo is of particular importance. The objective of the present study was to analyse mechanisms of immune tolerance in bovine pregnancy during peri-implantation. Simmental heifers inseminated with either cryopreserved spermatozoa or seminal plasma were killed 12, 15 or 18 days after oestrus. Uteri were flushed for the recovery of conceptuses and the ipsilateral intercaruncular endometrium was sampled for gene expression analysis. Indoleamine 2,3-dioxygenase (IDO) mRNA, coding for the initial enzyme of the kynurenine pathway, was 18-fold (P < 0.001) more abundant in the endometrium of Day 18 pregnant v. non-pregnant animals. Tandem mass spectrometry revealed a decrease of endometrial l-tryptophan (P = 0.0008), but an increase of l-kynurenine concentration (P = 0.005) from Day 12 to Day 18, suggesting increasing IDO activity (P < 0.03). An in vitro coculture model of endometrial cells showed an induction of IDO expression following interferon-τ exposure primarily in stroma cells, which was confirmed by in situ hybridisation localising IDO mRNA mainly in deep stroma cells. Immunohistochemical analysis revealed fewer CD45-positive leucocytes in the zona basalis of pregnant animals. Elevated IDO activity may reduce the presence of leucocytes in the pregnant endometrium, providing a possible mechanism for protecting the semi-allogenic conceptus from maternal rejection.

Actions and interactions of progesterone and estrogen on transcriptome profiles of the bovine endometrium

The aim of our study was to analyze endometrial gene expression profiles in ovariectomized cows treated with estradiol and/or progesterone by using microarray analysis. Clustering of differentially expressed genes allowed separation into distinct hormone response patterns. These patterns could be classified into independent and interdependent actions of the steroid hormones estrogen and progesterone. The use of ovariectomized cows and external administration of hormones identified a set of genes whose regulation depends on a progesterone priming effect. The progesterone-primed estrogen response comprises gene functions such as migration, cell differentiation, and cell adhesion and therefore may play a crucial role in tissue remodeling, as one of its key regulators in the endometrium, TGFB2, is among this group of progesterone-primed genes. Functional annotation analysis of the estrogen-responsive gene clusters shows a clear dominance of functions such as cell cycle, morphogenesis, and differentiation. The functional profile of the progesterone-responsive clusters is less clear but nevertheless shows some important fertility-related terms like luteinization, oocyte maturation, and catecholamine metabolism. We looked for putative regulators of the steroid hormone response in endometrium by searching for enriched transcription factor binding sites in the promoter regions of the genes with similar hormone response profile. This analysis identified transcription factors such as SP1, NFYA, FOXA2, IRF2, ESR1, and NOBOX as candidate regulators of gene expression in bovine endometrium treated with steroid hormones. Taken together, our data provide novel insights into the regulation of bovine endometrial physiology by steroid hormones.

Modulation of the maternal immune system by the pre-implantation embryo

Background

A large proportion of pregnancy losses occur during the pre-implantation period, when the developing embryo is elongating rapidly and signalling its presence to the maternal system. The molecular mechanisms that prevent luteolysis and support embryo survival within the maternal environment are not well understood. To gain a more complete picture of these molecular events, genome-wide transcriptional profiles of reproductive day 17 endometrial tissue were determined in pregnant and cyclic Holstein-Friesian dairy cattle.

Results

Microarray analyses revealed 1,839 and 1,189 differentially expressed transcripts between pregnant and cyclic animals (with ≥ 1.5 fold change in expression; P-value < 0.05, MTC Benjamini-Hochberg) in caruncular and intercaruncular endometrium respectively. Gene ontology and biological pathway analysis of differentially expressed genes revealed enrichment for genes involved in interferon signalling and modulation of the immune response in pregnant animals.

Conclusion

The maternal immune system actively surveys the uterine environment during early pregnancy. The embryo modulates this response inducing the expression of endometrial molecules that suppress the immune response and promote maternal tolerance to the embryo. During this period of local immune suppression, genes of the innate immune response (in particular, antimicrobial genes) may function to protect the uterus against infection.

Effect of elevated circulating progesterone concentration on bovine blastocyst development and global transcriptome following endoscopic transfer of in vitro produced embryos to the bovine oviduct

Elevated concentrations of circulating progesterone in the immediate postconception period have been associated with an increase in embryonic growth rate, interferon-tau production, and pregnancy rate in cattle and sheep. Much of this effect is likely mediated via downstream effects of progesterone-induced changes in gene expression in the uterine tissues. Using state-of-the-art endoscopic techniques, this study examined the effect of elevated progesterone on the development of in vitro produced bovine zygotes transferred to the oviducts of heifers with high or normal circulating progesterone concentrations and on the transcriptome of blastocysts developing under such conditions. Simmental heifers (n = 34) were synchronized using a controlled internal drug release (CIDR) device for 8 days, with a prostaglandin F(2 alpha) analogue administered 3 days before removal of the CIDR device. Only animals exhibiting a clear standing estrus (Day 0) were used. To produce animals with divergent progesterone concentrations, half of the animals received a progesterone-releasing intravaginal device (PRID) on Day 3 of the estrous cycle; the PRID was left in place until embryo recovery. All animals were sampled for blood daily from Day 0 to Day 7. Cleaved embryos were transferred by endoscopy to the ipsilateral oviduct of each recipient on Day 2 and then recovered by nonsurgically flushing the oviduct and the uterus on Day 7. The number of embryos developing to the blastocyst stage was recorded at recovery and following overnight culture in vitro. Potential effects of elevated progesterone on transcript abundance were examined using the Affymetrix GeneChip Bovine Genome Array. Insertion of a PRID on Day 3 resulted in a significant elevation of progesterone concentration (P < 0.05) from Day 3.5 until Day 6. Elevated progesterone did not affect the proportion of embryos developing to the blastocyst stage. Genomewide gene expression analysis identified 194 differentially expressed genes between embryos collected from heifers with normal or elevated progesterone, and quantitative real-time PCR validation with a subset of selected genes and an independent sample confirmed the microarray results. Interaction network analysis indicated a significant interaction between progesterone-regulated genes in the blastocyst and in the maternal endometrium. These results suggest that elevated concentrations of progesterone do not affect the ability of the early embryo to reach the blastocyst stage in vivo but do result in subtle changes to the transcriptome of the embryo that may be associated with advanced elongation posthatching.

Microarray analysis of equine endometrium at days 8 and 12 of pregnancy

Establishment and maintenance of pregnancy in equids is only partially understood. To provide new insights into early events of this process, we performed a systematic analysis of transcriptome changes in the endometrium at Days 8 and 12 of pregnancy. Endometrial biopsy samples from pregnant and nonpregnant stages were taken from the same mares. Composition of the collected biopsy samples was analyzed using quantitative stereological techniques to determine proportions of surface and glandular epithelium and blood vessels. Microarray analysis did not reveal detectable changes in gene expression at Day 8, whereas at Day 12 of pregnancy 374 differentially expressed genes were identified, 332 with higher and 42 with lower transcript levels in pregnant endometrium. Expression of selected genes was validated by quantitative real-time RT-PCR. Gene set enrichment analysis, functional annotation clustering, and cocitation analysis were performed to characterize the genes differentially expressed in Day 12 pregnant endometrium. Many known estrogen-induced genes and genes involved in regulation of estrogen signaling were found, but also genes known to be regulated by progesterone and prostaglandin E2. Additionally, differential expression of a number of genes related to angiogenesis and vascular remodeling suggests an important role of this process. Furthermore, genes that probably have conserved functions across species, such as CRYAB, ERRFI1, FGF9, IGFBP2, NR2F2, STC1, and TNFSF10, were identified. This study revealed the potential target genes and pathways of conceptus-derived estrogens, progesterone, and prostaglandin E2 in the equine endometrium probably involved in the early events of establishment and maintenance of pregnancy in the mare.

Differential endometrial gene expression in pregnant and nonpregnant sows

In an attempt to unveil molecular processes controlling the porcine placentation, we have investigated the pregnancy-induced gene expression in the endometrium using the Affymetrix GeneChip Porcine Genome Array. At Day 14 after insemination, at the time of initial placentation, samples were obtained from the endometrium of pregnant sows and sows inseminated with inactivated semen. Analysis of the microarray data revealed 263 genes to be significantly differentially expressed between the pregnant and nonpregnant sows. Most gene ontology terms significantly enriched at pregnancy had allocated more up-regulated genes than down-regulated genes. These terms included developmental process, transporter activity, calcium ion binding, apoptosis, cell motility, enzyme-linked receptor protein signaling pathway, positive regulation of cell proliferation, ion homeostasis, and hormone activity. Only the three terms oxidoreductase activity, lipid metabolic process, and organic acid metabolic process had an overrepresentation of down-regulated genes. A gene interaction network based on the genes identified in the gene ontology term developmental processes identified genes likely to be involved in the process of placentation. Pregnancy-specific localization of IL11RA to the surface epithelium of the endometrium suggests a role of interleukin 11 signaling in formation of the porcine epitheliochorial placenta. Furthermore, up-regulation of FGF9 mRNA in pregnant endometrium and localization of FGF9 to the apical cell domain of the glandular epithelium suggest the concept of endometrial FGF9 acting as an embryonic growth factor in the pig.

Bovine pretransfer endometrium and embryo transcriptome fingerprints as predictors of pregnancy success after embryo transfer

Aberrant gene expression in the uterine endometrium and embryo has been the major causes of pregnancy failure in cattle. However, selecting cows having adequate endometrial receptivity and embryos of better developmental competence based on the gene expression pattern has been a greater challenge. To investigate whether pretransfer endometrial and embryo gene expression pattern has a direct relation with upcoming pregnancy success, we performed a global endometrial and embryo transcriptome analysis using endometrial and embryo biopsy technology and the pregnancy outcome information. For this, endometrial samples were collected from Simmental heifers at day 7 and 14 of the estrous cycle, one cycle prior to embryo transfer. In the next cycle, blastocyst stage embryos were transferred to recipients at day 7 of the estrous cycle after taking 30-40% of the blastocyst as a biopsy for transcriptome analysis. The results revealed that at day 7 of the estrous cycle, the endometrial gene expression pattern of heifers whose pregnancy resulting in calf delivery was significantly different compared with those resulting in no pregnancy. These differences were accompanied by qualitative and quantitative alteration of major biological process and molecular pathways. However, the transcriptome difference was minimal between the two groups of animals at day 14 of the estrous cycle. Similarly, the transcriptome analysis between embryos biopsies that resulted in calf delivery and those resulted in no pregnancy revealed a total of 70 differentially expressed genes. Among these, the transcript levels of 32 genes including SPAG17, PF6, UBE2D3P, DFNB31, AMD1, DTNBP1, and ARL8B were higher in embryo biopsies resulting in calf delivery. Therefore, the present study highlights the potential of pretransfer endometrial and embryo gene expression patterns as predictors of pregnancy success in cattle.

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.

In vitro systems for intercepting early embryo-maternal cross-talk in the bovine oviduct

A comprehensive understanding of the complex embryo-maternal interactions during the preimplantation period requires the analysis of very early stages of pregnancy. These are difficult to assess in vivo due to the small size of the embryo exerting local paracrine effects. Specifically designed experiments and holistic transcriptome and proteome analyses to address the early embryo-maternal cross-talk in the oviduct require sufficient numbers of well-defined cells in a standardized experimental environment. The pronounced estrous cycle-dependent changes in gene expression and morphology of bovine oviduct epithelial cells (BOECs) clearly show that a precise definition of the stage of estrous cycle is essential for obtaining a well-defined homogenous population of functional cells. The number of intact cells isolated from individual ampullae by solely mechanical means was 10-fold higher than previously reported cell yields after enzymatic treatment, and the purity was comparable. Bovine oviduct epithelial cells have been cultured as monolayers or in suspension. Proliferating cells grown in monolayers dedifferentiated, with a concomitant loss of important morphologic characteristics. After several days in culture, BOECs in monolayers are less likely to mimic the oviduct environment in vivo than BOEC vesicles formed of epithelial sheets in short-term suspension culture. A 24-h culture system for BOECs isolated on Day 3.5 of the estrous cycle showed excellent preservation of morphologic criteria, marker gene expression, and hormone responsiveness. The short-term BOEC culture system provides well-defined and functional BOECs in sufficient quantities for studies of early embryo-maternal interactions in experiments that mimic the environment in the oviduct in vivo.

Evaluation of real-time PCR endogenous control genes for analysis of gene expression in bovine endometrium

Background

Quantitative real-time PCR gene expression results are generally normalised using endogenous control genes. These reference genes should be expressed at a constant level across all sample groups in a study, and should not be influenced by study treatments or conditions. There has been no systematic investigation of endogenous control genes for bovine endometrium to date. The suitability of both commonly used and novel endogenous control genes was evaluated in this study, with the latter being selected from stably expressed transcripts identified through microarray analysis of bovine endometrium. Fifteen candidate endogenous control genes were assessed across different tissue subtypes in pregnant and cycling Holstein-Friesian dairy cows from two divergent genetic backgrounds.

Results

The expression profiles of five commonly used endogenous control genes (GAPDH, PPIA, RPS9, RPS15A, and UXT) and 10 experimentally derived candidate endogenous control genes (SUZ12, C2ORF29, ZNF131, ACTR1A, HDAC1, SLC30A6, CNOT7, DNAJC17, BBS2, and RANBP10) were analysed across 44 samples to determine the most stably expressed gene. Gene stability was assessed using the statistical algorithms GeNorm and Normfinder. All genes presented with low overall variability (0.87 to 1.48% CV of Cq). However, when used to normalise a differentially expressed gene (oxytocin receptor - OXTR) in the samples, the reported relative gene expression levels were significantly affected by the control gene chosen. Based on the results of this analysis, SUZ12 is proposed as the most appropriate control gene for use in bovine endometrium during early pregnancy or the oestrus cycle.

Conclusion

This study establishes the suitability of novel endogenous control genes for comparing expression levels in endometrial tissues of pregnant and cycling bovines, and demonstrates the utility of microarray analysis as a method for identifying endogenous control gene candidates.

Germ-line transmission of lentiviral PGK-EGFP integrants in transgenic cattle: new perspectives for experimental embryology

Lentiviral vectors are a powerful tool for the genetic modification of livestock species. We previously generated transgenic founder cattle with lentiviral integrants carrying enhanced green fluorescent protein (EGFP) under the control of the phosphoglycerate kinase (PGK) promoter. In this study, we investigated the transmission of LV-PGK-EGFP integrants through the female and male germ line in cattle. A transgenic founder heifer (#562, Kiki) was subjected to superovulation treatment and inseminated with semen from a non-transgenic bull. Embryos were recovered and transferred to synchronized recipient heifers, resulting in the birth of a healthy male transgenic calf expressing EGFP as detected by in vivo imaging. Semen from a transgenic founder bull (#561, Jojo) was used for in vitro fertilization (IVF) of in vitro matured (IVM) oocytes from non-transgenic cows. The rates of cleavage and development to blastocyst in vitro corresponded to 52.0 +/- 4.1 and 24.5 +/- 4.4%, respectively. Expression of EGFP was observed at blastocyst stage (day 7 after IVF) and was seen in 93.0% (281/302) of the embryos. 24 EGFP-expressing embryos were transferred to 9 synchronized recipients. Analysis of 2 embryos, flushed from the uterus on day 15, two fetuses recovered on day 45, and a healthy male transgenic calf revealed consistent high-level expression of EGFP in all tissues investigated. Our study shows for the first time transmission of lentiviral integrants through the germ line of female and male transgenic founder cattle. The pattern of inheritance was consistent with Mendelian rules. Importantly, high fidelity expression of EGFP in embryos, fetuses, and offspring of founder #561 provides interesting tools for developmental studies in cattle, including interactions of gametes, embryos and fetuses with their maternal environment.

Progesterone and conceptus elongation in cattle: a direct effect on the embryo or an indirect effect via the endometrium?

The steroid hormone progesterone (P4) plays a key role in the reproductive events associated with pregnancy establishment and maintenance. High concentrations of circulating P4 in the immediate post-conception period have been associated with an advancement of conceptus elongation, an associated increase in interferon-τ production and higher pregnancy rates in cattle. Using in vitro and in vivo models and ∼8500 bovine oocytes across six experiments, the aim of this study was to establish the route through which P4 affects bovine embryo development in vitro and in vivo. mRNA for P4 receptors was present at all stages of embryo development raising the possibility of a direct effect of P4 on the embryo. Exposure to P4 in vitro in the absence or presence of oviduct epithelial cells did not affect the proportion of embryos developing to the blastocyst stage, blastocyst cell number or the relative abundance of selected transcripts in the blastocyst. Furthermore, exposure to P4 in vitro did not affect post-hatching elongation of the embryo following transfer to synchronized recipients and recovery on Day 14. By contrast, transfer of in vitro derived blastocysts to a uterine environment previously primed by elevated P4 resulted in a fourfold increase in conceptus length on Day 14. These data provide clear evidence to support the hypothesis that P4-induced changes in the uterine environment are responsible for the advancement in conceptus elongation reported previously in cattle and that, interestingly, the embryo does not need to be present during the period of high P4 in order to exhibit advanced elongation.

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.

Gene expression profiles of bovine caruncular and intercaruncular endometrium at implantation

At implantation the endometrium undergoes modifications necessary for its physical interactions with the trophoblast as well as the development of the conceptus. We aim to identify endometrial factors and pathways essential for a successful implantation in the caruncular (C) and the intercaruncular (IC) areas in cattle. Using a 13,257-element bovine oligonucleotide array, we established expression profiles at day 20 of the estrous cycle or pregnancy (implantation), revealing 446 and 1,295 differentially expressed genes (DEG) in C and IC areas, respectively (false discovery rate = 0.08). The impact of the conceptus was higher on the immune response function in C but more prominent on the regulation of metabolism function in IC. The C vs. IC direct comparison revealed 1,177 and 453 DEG in cyclic and pregnant animals respectively (false discovery rate = 0.05), with a major impact of the conceptus on metabolism and cell adhesion. We selected 15 genes including C11ORF34, CXCL12, CXCR4, PLAC8, SCARA5, and NPY and confirmed their differential expression by quantitative RT-PCR. The cellular localization was analyzed by in situ hybridization and, upon pregnancy, showed gene-specific patterns of cell distribution, including a high level of expression in the luminal epithelium for C11ORF34 and MX1. Using primary cultures of bovine endometrial cells, we identified PTN, PLAC8, and CXCL12 as interferon-tau (IFNT) target genes and MSX1 and CXCR7 as IFNT-regulated genes, whereas C11ORF34 was not an IFNT-regulated gene. Our transcriptomic data provide novel molecular insights accounting for the biological functions related to the C or IC endometrial areas and may contribute to the identification of potential biomarkers for normal and perturbed early pregnancy.

Dickkopf-1 expression during early bovine placentation and its down-regulation in somatic cell nuclear transfer (SCNT) pregnancies

The precise role of Dickkopf-1 (Dkk-1) during early bovine trophoblast development and subsequent placentation is not fully understood. Using somatic cell nuclear transfer (SCNT) generated pregnancies as a model of poor placentation we have found that mean levels of Dkk-1 mRNA were 1.5 fold lower in SCNT fetal cotyledon tissue at Day 50 of gestation than those resulting from artificial insemination (AI) and 2 fold lower at Days 100 and 150 (P<0.004). Dkk-1 expression in cotyledon tissue was localized by in situ hybridization to fetal binucleate cells (BNCs). Examining conceptuses from blastocyst stage we show that Dkk-1 mRNA was first evident between Days 15-20 of gestation in trophoblast tissue (when BNCs first appear) prior to the initial expression of the BNC specific bovine placental lactogen (bPL) on Day 20. Dkk-1 mRNA levels were higher than bPL in trophoblast tissue throughout the pre-attachment period (Days 24-31), however, this reversed during cotyledon development with only a subset of the bPL immunoreactive BNCs also containing Dkk-1 protein, suggesting a specific role for Dkk-1 during early placentation. One function of Dkk-1 is as an antagonist of the Wnt signaling pathway and, although Wnt5A and Wnt7A mRNAs were expressed in Day 50 bovine cotyledons, their expression levels were similar between AI and SCNT. In addition, the nuclear localization of beta-catenin, which is an indicator of activation of the Wnt pathway, was also similar between AI and SCNT cotyledon tissue. Transcriptional control of Dkk-1 was not due to changes in DNA methylation levels in the promoter region as methylation levels were no different when comparing AI and SCNT tissues. The decreased expression of Dkk-1 in SCNT cotyledons that are prone to abnormal placentation suggests a role in cotyledon formation but the mechanism and regulatory control is yet to be revealed.

The endometrium responds differently to cloned versus fertilized embryos

Although somatic cell nuclear transfer (SCNT) cloning is more efficient in cattle than in any other species tested so far, there is a high rate of pregnancy failure that has been linked to structural and functional abnormalities of the placenta. We tested the hypothesis that these changes may originate from disturbed embryo-maternal interactions in the peri-implantation period. Therefore, we evaluated the response of the endometrium to SCNT embryos (produced from 7 different fetal fibroblast cell lines) as compared with embryos derived from in vitro fertilization (IVF). SCNT embryos and IVF embryos were cultured under identical conditions to the blastocyst stage (day 7) and were transferred to corresponding recipients, which were slaughtered at day 18 of pregnancy. The mRNA profiles of endometrium samples were obtained using a custom cDNA microarray enriched for transcripts differentially expressed in the endometrium and/or oviduct epithelium during the estrous cycle and/or early pregnancy. Overall, the variation in mRNA profiles was greater in the SCNT group than in the IVF group. Furthermore, 58 transcripts were differentially abundant in endometria from SCNT and IVF pregnancies. Prominent examples are orphan nuclear receptor COUP-TFII and connexin 43, both known to play important roles in uterine receptivity and conceptus placentation. These findings suggest that placental failure in bovine clone pregnancies may originate from abnormal embryo-maternal communication that develops during the peri-implantation period. Endometrium transcriptome profiles may serve as a tool to evaluate SCNT embryos for their ability to establish pregnancy and develop a functional placenta.

Endometrium as an early sensor of in vitro embryo manipulation technologies

Implantation is crucial for placental development that will subsequently impact fetal growth and pregnancy success with consequences on postnatal health. We postulated that the pattern of genes expressed by the endometrium when the embryo becomes attached to the mother uterus could account for the final outcome of a pregnancy. As a model, we used the bovine species where the embryo becomes progressively and permanently attached to the endometrium from day 20 of gestation onwards. At that stage, we compared the endometrial genes profiles in the presence of an in vivo fertilized embryo (AI) with the endometrial patterns obtained in the presence of nuclear transfer (SCNT) or in vitro fertilized embryos (IVF), both displaying lower and different potentials for term development. Our data provide evidence that the endometrium can be considered as a biological sensor able to fine-tune its physiology in response to the presence of embryos whose development will become altered much later after the implantation process. Compared with AI, numerous biological functions and several canonical pathways with a major impact on metabolism and immune function were found to be significantly altered in the endometrium of SCNT pregnancies at implantation, whereas the differences were less pronounced with IVF embryos. Determining the limits of the endometrial plasticity at the onset of implantation should bring new insights on the contribution of the maternal environment to the development of an embryo and the success of pregnancy.

Bovine endometrial legumain and TIMP-2 regulation in response to presence of a conceptus

The precise mechanism of placentation in the bovine species where a restricted trophoblast invasion occurs to form the synepitheliochorial placenta is not fully understood. This study initially investigated the conceptus-maternal interactions in the peri-attachment period by comparing the proteins present at Days 16 and 18 in uterine luminal fluid (ULF) of pregnant with nonpregnant cows using 2-D gel electrophoresis. Nine protein spots were identified that were present in greater amounts in pregnant compared to nonpregnant ULF: carbonic anhydrase, ezrin, heat shock protein 70, isocitrate dehydrogenase, nucleoside diphosphate kinase, peroxiredoxin 1, purine nucleoside phosphorylase, thioredoxin and triosephosphate isomerase and four proteins that were less abundant in ULF from the gravid compared to the nongravid horns or nonpregnant uteri: cystatin E/M, legumain, retinol-binding protein (RBP) and tissue inhibitor of matrix metalloproteinase 2 (TIMP-2). Successful placentation requires the remodelling of the endometrial surface therefore uterine mRNA and protein expression of legumain, a protease activator, and TIMP-2, a protease inhibitor, was examined in detail during the oestrous cycle and from Days 13 to 31 of pregnancy. Both mRNAs were up-regulated in the endometrium during the luteal phase of the oestrous cycle and during early pregnancy. Although legumain and TIMP-2 mRNA expression levels were similar between uterine horns at the same day of pregnancy, the amount of protein differed between gravid and nongravid horns possibly modulated by interferon-tau or by other factors produced by the conceptus. These events at the conceptus-maternal interface may provide localised control of protease activity necessary for controlling trophoblast invasion of the endometrium.