Function of a transcription factor CDX2 beyond its trophectoderm lineage specification

Effect of antifreeze protein I in the freezing solution on in vivo-derived sheep embryos

This study evaluated the effects of different antifreeze protein type I (AFP I) concentrations added to a slow freezing solution in sheep in vivo-derived embryos. Good-quality embryos were allocated into: AFP-free (CONT); 0.1 μg/mL of AFP I (AFP0.1); or 0.5 μg/mL of AFP I (AFP0.5). After thawing, embryos were in vitro cultured (IVC) for 48 h. At 24 h and 48 h of IVC, dead cells and apoptosis, mitochondrial activity, intracellular reactive oxygen species (ROS), and glutathione (GSH) evaluations were performed. At 24 h, evaluated embryos were submitted to RT-qPCR for metabolism (SIRT2, PRDX1, OCT4, CDX2) and quality (AQP3, CDH1, HSP70, BAX, BCL2) genes. The in vitro survival rate was 56% (22/39) for CONT, 60% (32/53) for AFP0.1, and 53% (23/43) for AFP0.5 (p > 0.05). A tendency (p = 0.09) for a higher blastocyst hatching rate was noted in AFP0.1 (62%) compared to AFP0.5 (33%), and both groups were similar to CONT (50%). An increased (p < 0.05) mitochondrial activity at 24 h was observed in AFP0.1 compared to CONT. No differences (p > 0.05) were observed in oxidative stress homeostasis and viability between treatments. A downregulation (p < 0.05) of CDH1 in AFP0.1 and a downregulation of AQP3 in AFP0.5 were observed in comparison to the other groups. An upregulation (p < 0.05) was detected in HSP70 and BCL2 on AFP0.5 compared to AFP0.1 group. The addition of AFP I in slow freezing solution can benefit cryopreserved sheep in vivo-derived embryos, without affecting embryonic survival.

Early Cell Specification in Mammalian Fertilized and Somatic Cell Nuclear Transfer Embryos

Early cell specification in mammalian preimplantation embryos is an intricate cellular process that leads to coordinated spatial and temporal expression of specific genes. Proper segregation into the first two cell lineages, the inner cell mass (ICM) and the trophectoderm (TE), is imperative for developing the embryo proper and the placenta, respectively. Somatic cell nuclear transfer (SCNT) allows the formation of a blastocyst containing both ICM and TE from a differentiated cell nucleus, which means that this differentiated genome must be reprogrammed to a totipotent state. Although blastocysts can be generated efficiently through SCNT, the full-term development of SCNT embryos is impaired mostly due to placental defects. In this review, we examine the early cell fate decisions in fertilized embryos and compare them to observations in SCNT-derived embryos, in order to understand if these processes are affected by SCNT and could be responsible for the low success of reproductive cloning.

Epithelial-mesenchymal transition and bi- and multi-nucleated trophoblast cell formation in ovine conceptuses during the peri-implantation period

Epithelial-mesenchymal transition (EMT), which is common in cancer metastasis, is also observed during developmental processes such as embryo implantation into the maternal endometrium in humans and rodents. However, this process has not been well characterized in the non-invasive type of implantation that occurs in ruminants. To understand whether EMT occurs in ruminant ungulates, ovine conceptuses (embryo plus extraembryonic membranes) from days 15 (P15: pre-attachment), 17 (P17: during attachment), and 21 (P21: post-attachment, day 0 = day of estrus) were evaluated. RNA-seq analysis revealed that the expression of EMT-related transcripts increased on P21. Real-time PCR and western blotting analyses indicated that levels of transcripts and proteins indicative of mesenchyme-related molecules increased on P21, but a minor expression of epithelium-related molecules remained. Immunohistochemical analysis revealed that E-cadherin (CDH1) was localized in the elongated trophectoderm on P15 and P17. On P21, CDH1 was localized to the trophectoderm and on the conceptus cells undergoing differentiation. Vimentin (VIM) was localized in the uterine stroma on P15 and P17, and its expression was observed at the edge of elongating trophoblast on P21. Further, it was found that some bi-nucleated trophoblast cells were present on P17; however, numerous bi- and multi-nucleated trophoblast cells on the uterine epithelium or next to the uterine stroma were found on P21. A minor expression of pregnancy-associated glycoprotein (PAG) transcripts was found on P15 and P17, but a definitive expression of PAGs, transcripts, and proteins was found on P21. Although further investigation is required, these observations indicate that bi-nucleated trophoblast cell formation begins on the day conceptus implantation to the maternal endometrium is initiated, followed by EMT in trophoblast cells. These results suggest that these sequential events are required if pregnancy is to be established in ruminants.

Overexpression of miR-210-3p Impairs Extravillous Trophoblast Functions Associated with Uterine Spiral Artery Remodeling

Hsa-miR-210-3p has been reported to be upregulated in preeclampsia (PE); however, the functions of miR-210-3p in placental development are not fully understood, and, consequently, miR-210-3p’s role in the pathogenesis of PE is still under investigation. In this study, we found that overexpression of miR-210-3p reduced trophoblast migration and invasion, extravillous trophoblast (EVT) outgrowth in first trimester explants, expression of endovascular trophoblast (enEVT) markers and the ability of trophoblast to form endothelial-like networks. In addition, miR-210-3p overexpression significantly downregulated the mRNA levels of interleukin-1B and -8, as well as CXC motif ligand 1. These cytokines have been suggested to play a role in EVT invasion and the recruitment of immune cells to the spiral artery remodeling sites. We also showed that caudal-related homeobox transcription factor 2 (CDX2) is targeted by miR-210-3p and that CDX2 downregulation mimicked the observed effects of miR-210-3p upregulation in trophoblasts. These findings suggest that miR-210-3p may play a role in regulating events associated with enEVT functions and its overexpression could impair spiral artery remodeling, thereby contributing to PE.

Characterisation of bovine embryos following prolonged culture in embryonic stem cell medium containing leukaemia inhibitory factor

In order to help elucidate the process of epiblast and trophoblast cell differentiation in bovine embryos invitro, we attempted to develop a suitable culture medium to allow extended embryo culture. Day 7 bovine blastocysts developed in conventional medium were cultured further in embryonic stem cell medium with or without leukaemia inhibitory factor (LIF) until Day 23. At Day 14, the expression of octamer-binding transcription factor 3/4 (OCT3/4) and VIMENTIN was significantly higher in embryos cultured with than without LIF, but embryonic disc formation was not observed. Although expression of SRY (sex determining region Y)-box 17 (SOX17) mRNA was significantly lower in Day 14 embryos cultured with and without LIF than in invivo embryos, hypoblast cells formed just inside the trophoblast cells of the invitro-cultured embryos. On Day 23, expression of placental lactogen (PL) and prolactin-related protein 1 (PRP1) was not affected by LIF in invitro-cultured embryos, levels of both genes were significantly lower in the invitro than invivo embryos. Similar to invivo embryos, binucleate cell clusters seen in Day 23invitro-cultured embryos were composed of PL-negative and -positive cells. These results suggest that our culture system partially reproduced the differentiation process of trophoblast cells invivo.

Gene expression patterns of in vivo-derived sheep blastocysts is more affected by vitrification than slow freezing technique

Transfer of fresh sheep embryos frequently results in higher pregnancy rate compared to cryopreserved ones, possibly due to a failure in the communication between the cryopreserved embryo and the endometrium during pre-implantation and pregnancy establishment. Thus, this study assessed the effect of sheep embryo cryopreservation (slow freezing or vitrification) on embryo survival rate and expression of genes related to trophectoderm differentiation (CDX2), pluripotency maintenance (NANOG), cell proliferation (TGFB1), mitochondrial activity (NRF1) and apoptosis (BAX and BCL2). Superovulation (n = 32 ewes) was performed and embryos were transcervically collected. One hundred good quality (Grade I and II) embryos were allocated into three groups: fresh embryos (CTL; n = 15), slow freezing (SF; n = 42) or vitrification (VT; n = 43). After thawing/warming, three pools of five blastocysts per group were used for RT-qPCR; the remaining 55 embryos were cultured in vitro in SOFaa medium at 38.5 °C and 5% CO₂ (SF: n = 27 and VT: n = 28). Survival rate of SF and VT were, respectively, 29.6% (8/27) and 14.2% (4/28) at 24 h; and 48.1% (13/27) and 32.1% (9/28) at 48 h (P > 0.05). Only CDX2 was affected (up-regulated, P < 0.05) in both groups compared to CTL. The BAX transcript was upregulated in VT, compared to SF group. The VT increased (P < 0.05) the expression of all genes, except for NANOG and NRF1, when compared to the CTL. In conclusion, although in vitro survival was similar between techniques, VT led to increased changes in blastocyst gene expression compared to CTL and SF.

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

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

Procedures for chemical fixation in immunohistochemical analyses of PIN proteins regulating polar auxin transport: Relevance to spaceflight experiments

The mechanism by which gravity controls the polar transport of auxin, a plant hormone regulating multiple physiological processes in higher plants, remains unclear, although an important role of PIN proteins as efflux carriers/facilitators in polar auxin transport is suggested. We are going to study the effect of microgravity on the polar transport of auxin, focusing on the cellular localization of its efflux carrier, PsPIN1 in etiolated pea seedlings and ZmPIN1a in etiolated maize seedlings grown under microgravity conditions on the International Space Station (ISS) using immunohistochemical analyses according to space experimental plans (Ueda, 2016). To obtain adequate results regarding the cellular localization of functional proteins, prolonged chemical fixation processes as well as chemical fixatives should be well-matched to the properties of functional proteins as antigens since experimental analyses will be performed on the ground after keeping samples for a long duration on the ISS. As a result of ground verification, clear detection of the cellular localization of PsPIN1 and ZmPIN1a immunohistochemically was successful based on the results of several kinds of chemical fixation tested, even when etiolated pea and maize seedlings were fixed by immersion in chemical fixative for a long duration. The addition of 0.1% (w/v) Nonidet P-40 to chemical fixative composed of 50% (v/v) ethanol and 5% (v/v) acetic acid or that of 50% (v/v) methanol and 5% (v/v) acetic acid has led to a significant improvement in the immunohistochemical detection of PsPIN1 or ZmPIN1a. These chemical fixatives were also shown to be storage-stable for a long time before use. In this study, adequate chemical fixatives and fixation protocols were developed, which can be used to detect localization of PsPIN1 and ZmPIN1a proteins in young etiolated pea and maize seedlings, respectively, using anti PsPIN1 and ZmPIN1a antibodies. These protocols can be used in spaceflight experiments to investigate the effects of the microgravity environment on the ISS on PIN protein localization in pea and maize seedlings.

Down-regulation of transcription factor OVOL2 contributes to epithelial-mesenchymal transition in a noninvasive type of trophoblast implantation to the maternal endometrium

Embryo implantation into the uterine endometrium is required for pregnancy establishment in most mammals. By using global expression analysis, we investigated the molecules that are related to epithelial-mesenchymal transition (EMT) in noninvasive bovine trophoblasts and found that the transcription factor, ovo-like zinc finger 2 ( OVOL2), which is essential for mesenchymal-epithelial transition in various cancers, was down-regulated after trophoblast attachment to the endometrial epithelium in utero. In cultured bovine trophoblast cells, OVOL2 down-regulation occurred only when cells were allowed to attach to bovine endometrial epithelial cells via the TEAD3/YAP signaling pathway. This resulted in the up-regulation of the EMT-associated transcription factors, ZEB1 and SNAI2, and the mesenchymal cell markers, N-cadherin ( CDH2) and vimentin ( VIM), whereas epithelial cell marker, E-cadherin ( CDH1), was down-regulated. In contrast, OVOL2 overexpression in bovine trophoblast cells exhibited a decrease in ZEB1 transcripts and an increase in E-cadherin. These observations revealed that ovo-like protein (OVOL)2 down-regulation occurred concurrently with conceptus implantation into the uterine endometrium via the YAP/TEAD3 signaling pathway, and suggest that the down-regulation of OVOL2 expression contributes to the up-regulation of EMT-related transcription factor expression, which enables EMT progression in the noninvasive bovine trophectoderm postimplantation.-Bai, R., Kusama, K., Nakamura, K., Sakurai, T., Kimura, K., Ideta, A., Aoyagi, Y., Imakawa, K. Down-regulation of transcription factor OVOL2 contributes to epithelial-mesenchymal transition in a noninvasive type of trophoblast implantation to the maternal endometrium.

Transcriptional control of IFNT expression

Once interferon-tau (IFNT) had been identified as a type I IFN in sheep and cattle and its functions were characterized, numerous studies were conducted to elucidate the transcriptional regulation of this gene family. Transfection studies performed largely with human choriocarcinoma cell lines identified regulatory regions of the IFNT gene that appeared responsible for trophoblast-specific expression. The key finding was the recognition that the transcription factor ETS2 bound to a proximal region within the 5'UTR of a bovine IFNT and acted as a strong transactivator. Soon after other transcription factors were identified as cooperative partners. The ETS2-binding site and the nearby AP1 site enable response to intracellular signaling from maternal uterine factors. The AP1 site also serves as a GATA-binding site in one of the bovine IFNT genes. The homeobox-containing transcription factor, DLX3, augments IFNT expression combinatorially with ETS2. CDX2 has also been identified as transactivator that binds to a separate site upstream of the main ETS2 enhancer site. CDX2 participates in IFNT epigenetic regulation by modifying histone acetylation status of the gene. The IFNT downregulation at the time of the conceptus attachment to the uterine endometrium appears correlated with the increased EOMES expression and the loss of other transcription coactivators. Altogether, the studies of transcriptional control of IFNT have provided mechanistic evidence of the regulatory framework of trophoblast-specific expression and critical expression pattern for maternal recognition of pregnancy.

A transcriptional cofactor YAP regulates IFNT expression via transcription factor TEAD in bovine conceptuses

Interferon tau (IFNT) is the pregnancy recognition protein in all ruminants, and its expression is restricted to trophoblast cells. Interferon tau production increases as the conceptus elongates; however, its expression is downregulated soon after the initiation of conceptus attachment to the uterine epithelium. Our previous study identified that among 8 bovine IFNT genes, only 2 forms of IFNTs, IFNT2 and IFN-tau-c1, were expressed by the conceptuses during the periattachment period. To characterize whether Hippo signaling including a transcription cofactor yes-associated protein (YAP) was involved in the IFNT regulation, we examined the expression and effects of YAP and/or TEAD in human choriocarcinoma JEG3 and bovine trophoblast CT-1 cells, and in bovine conceptuses obtained from day 17, 20 or 22 pregnant animals (pregnant day 19.5 = day of conceptus attachment to the endometrium). YAP was expressed in bovine conceptuses and transfection of YAP or TEAD4, a transcription factor partner of YAP, expression plasmid increased the luciferase activity of IFNT2 and IFN-tau-c1 reporter plasmids in JEG3 cells. In the presence of YAP expression plasmid, TEAD2 or TEAD4 expression plasmid further upregulated transcriptional activity of IFNT2 or IFN-tau-c1 constructs, which were substantially reduced in the absence of the TEAD-binding site on IFNT2 or IFN-tau-c1 promoter region in JEG3 cells. In CT-1 cells, treatment with TEAD2, TEAD4, or YAP small-interfering RNA downregulated endogenous IFNT expression. It should be noted that TEAD2 and TEAD4 were predominantly localized in the nuclei of trophectoderm of Day 17 conceptuses, but nuclear localization appeared to be lower in those cells of conceptuses on days 20 and 22 of pregnancy. Moreover, the binding of TEAD4 to the TEAD-binding site of the IFN-tau-c1 promoter region in day 17 conceptuses was less in day 20 and 22 conceptuses. Furthermore, the level of YAP phosphorylation increased in day 20 and 22 conceptuses. These results indicated that although YAP/TEAD had the ability to up-regulate IFNT gene transcription on day 17, IFNT2 or IFN-tau-c1 was down-regulated following changes in the localization of TEAD2 and TEAD4 from the nucleus to the cytoplasm and increases in phosphorylation and degradation of YAP. These data suggest that TEAD relocation and/or YAP degradation following its phosphorylation down-regulates IFNT gene transcription after conceptus attachment to the uterine endometrium.

HP1BP3, a Chromatin Retention Factor for Co-transcriptional MicroRNA Processing

Recent studies suggest that the microprocessor (Drosha-DGCR8) complex can be recruited to chromatin to catalyze co-transcriptional processing of primary microRNAs (pri-miRNAs) in mammalian cells. However, the molecular mechanism of co-transcriptional miRNA processing is poorly understood. Here we find that HP1BP3, a histone H1-like chromatin protein, specifically associates with the microprocessor and promotes global miRNA biogenesis in human cells. Chromatin immunoprecipitation (ChIP) studies reveal genome-wide co-localization of HP1BP3 and Drosha and HP1BP3-dependent Drosha binding to actively transcribed miRNA loci. Moreover, HP1BP3 specifically binds endogenous pri-miRNAs and facilitates the Drosha/pri-miRNA association in vivo. Knockdown of HP1BP3 compromises pri-miRNA processing by causing premature release of pri-miRNAs from the chromatin. Taken together, these studies suggest that HP1BP3 promotes co-transcriptional miRNA processing via chromatin retention of nascent pri-miRNA transcripts. This work significantly expands the functional repertoire of the H1 family of proteins and suggests the existence of chromatin retention factors for widespread co-transcriptional miRNA processing.

Induction of IFNT-Stimulated Genes by Conceptus-Derived Exosomes during the Attachment Period

Biochemical and/or physical communication between the conceptus and the uterine endometrium is required for conceptus implantation to the maternal endometrium, leading to placentation and the establishment of pregnancy. We previously reported that in vitro co-culture system with bovine trophoblast CT-1 cells, primary uterine endometrial epithelial cells (EECs), and uterine flushings (UFs) mimics in vivo conceptus attachment process. To identify molecules in UFs responsible for this change, we first characterized protein contents of UFs from day 17 cyclic (C17) and pregnant (P17) ewes through the use of two dimensional-Polyacrylamide Gel Electrophoresis (2D-PAGE), followed by Liquid Chromatography-tandem Mass Spectrometry (LC-MS/MS) analysis. These analyses identified 266 proteins specific for P17 UFs, from which 172 proteins were identified as exosomal proteins. Among 172 exosomal proteins, 8 proteins that had been identified as exosomal proteins were chosen for further analysis, including macrophage-capping protein (CAPG), aldo-keto reductase family 1, member B1 protein (AKR1B1), bcl-2-like protein 15 (BCL2L15), carbonic anhydrase 2 (CA2), isocitrate dehydrogenase 2 (IDH2), eukaryotic translation elongation factor 2 (EEF2), moesin (MSN), and ezrin (EZR). CAPG and AKR1B1 were again confirmed in P15 and P17 UFs, and more importantly CAPG and AKR1B1, mRNA and protein, were found only in P15 and P17 conceptuses. Moreover, exosomes were isolated from C15, C17, P15, or P17 UFs. Only P15 and P17 exosomes, originated from the conceptus, contained interferon tau (IFNT) as well as CAPG and AKR1B1, and up-regulated STAT1, STAT2, MX1, MX2, BST2, and ISG15 transcripts in EECs. These observations indicate that in addition to endometrial derived exosomes previously described, conceptus-derived exosomes are present in UFs and could function to modify endometrial response. These results suggest that exosomes secreted from conceptuses as well as endometria are involved in cell to cell interactions for conceptus implantation to the maternal endometrium.

Localization of GATA2 in the nuclear and cytoplasmic regions of ovine conceptuses

GATA transcription factors are emerging as critical regulators in trophoblast development and its gene regulation. The purpose of this study was to examine the expression and cellular localization of GATA2 in ovine conceptuses during the peri-implantation period. In Western blot analyses, GATA2 proteins were found in days 15, 17 and 21 ovine conceptuses (day 0=day of estrus). Using immunohistochemistry and immunofluorescence analyses, we found that GATA2 was localized in days 15, 17 and 21 ovine conceptuses, and more importantly, GATA2 protein was detected in both nuclear and cytoplasmic regions of the trophectoderm. To our knowledge, the present study is the first to demonstrate that GATA2 is localized in two cellular compartments of the trophectoderm in ovine and many other mammalian species, and suggests that the difference in GATA2 location plays a role in the regulation of down-stream genes during the early pregnancy period.

Presence of Transcription Factor OCT4 Limits Interferon-tau Expression during the Pre-attachment Period in Sheep

Interferon-tau (IFNT) is thought to be the conceptus protein that signals maternal recognition of pregnancy in ruminants. We and others have observed that OCT4 expression persists in the trophectoderm of ruminants; thus, both CDX2 and OCT4 coexist during the early stages of conceptus development. The aim of this study was to examine the effect of CDX2 and OCT4 on IFNT gene transcription when evaluated with other transcription factors. Human choriocarcinoma JEG-3 cells were cotransfected with an ovine IFNT (-654-bp)-luciferase reporter (-654-IFNT-Luc) construct and several transcription factor expression plasmids. Cotransfection of the reporter construct with Cdx2, Ets2 and Jun increased transcription of -654-IFNT-Luc by about 12-fold compared with transfection of the construct alone. When cells were initially transfected with Oct4 (0 h) followed by transfection with Cdx2, Ets2 and/or Jun 24 h later, the expression of -654-IFNT-Luc was reduced to control levels. OCT4 also inhibited the stimulatory activity of CDX2 alone, but not when CDX2 was combined with JUN and/or ETS2. Thus, when combined with the other transcription factors, OCT4 exhibited little inhibitory activity towards CDX2. An inhibitor of the transcriptional coactivator CREB binding protein (CREBBP), 12S E1A, reduced CDX2/ETS2/JUN stimulated -654-IFNT-Luc expression by about 40%, indicating that the formation of an appropriate transcription factor complex is required for maximum expression. In conclusion, the presence of OCT4 may initially minimize IFNT expression; however, as elongation proceeds, the increasing expression of CDX2 and formation of the transcription complex leads to greatly increased IFNT expression, resulting in pregnancy establishment in ruminants.

Expression and in situ localization of GATA4, 5 and 6 mRNAs in ovine conceptuses and uterine endometria during the peri-implantation period

In vertebrates, six GATA transcription factors, GATA1 through GATA6, have been identified and GATA1-3 is known to be involved in hematopoietic developments, while GATA4-6 play roles in cardiac and endoderm developments. Recently, we and others have found that GATA2 and GATA3 found in the trophectoderm plays a role in gene expression specific to this cell type, but GATA4-6 have not been well characterized in early embryonic developments. Using quantitative polymerase chain reaction (qPCR) and in situ hybridization, we examined the expression of GATA4, 5 and 6 messenger RNAs (mRNAs) in ovine conceptuses and uteri during the peri-implantation period. In ovine conceptuses, GATA4, 5 and 6 transcripts were present on days 15, 17 and 21 (day 0 = day of mating), and high GATA5 and 6 mRNAs were found on day 21, most of which were localized in the trophectoderm and endoderm. Moreover, minute and substantial GATA4 and 5 mRNAs were found in days 15 and 21 uterine endometria, respectively. Increase in GATA4-6 transcripts in day 21 uteri indicates that in addition to GATA1-3, GATA4-6 may also play a potentially novel role in the development of ovine trophectoderm, endoderm and/or uterine endometria following conceptus attachment to the uterine epithelium.

Transcriptional regulation of two conceptus interferon tau genes expressed in Japanese black cattle during peri-implantation period

Interferon tau (IFNT), produced by the mononuclear trophectoderm, signals the process of maternal recognition of pregnancy in ruminants. However, its expression in vivo and its transcriptional regulation are not yet well characterized. Objectives of this study were to determine conceptus IFNT gene isoforms expressed in the bovine uterus and to identify differences in promoter sequences of IFNT genes that differ in their expression. RNA-seq data analysis of bovine conceptuses on days 17, 20, and 22 (day 0  =  day of estrus) detected the expression of two IFNT transcripts, IFNT1 and IFNTc1, which were indeed classified into the IFNT gene clade. RNA-seq and quantitative RT-PCR analyses also revealed that the expression levels of both IFNT mRNAs were highest on day 17, and then decreased on days 20 and 22. Bovine ear-derived fibroblast (EF) cells, a model system commonly used for bovine IFNT gene transcription study in this laboratory, were cotransfected with luciferase reporter constructs carrying upstream (positions -637 to +51) regions of IFNT1 or IFNTc1 gene and various transcription factor expression plasmids including CDX2, AP-1 (Jun) and ETS2. CDX2, either alone or with the other transcription factors, markedly increased luciferase activity. The upstream regions of IFNT1 and IFNTc1 loci were then serially deleted or point-mutated at potential CDX-, AP-1-, and ETS-binding sites. Compared to the wild-type constructs, deletion or mutation at CDX2 or ETS2 binding sites similarly reduced the luciferase activities of IFNT1- or IFNTc1-promoter constructs. However, with the AP-1 site mutated construct, IFNT1- and IFNTc1-reporters behaved differently. These results suggest that two forms of bovine conceptus IFNT genes are expressed in utero and their transcriptional regulations differ.

Down-regulation of interferon tau gene transcription with a transcription factor, EOMES

Interferon tau (IFNT), produced for a short interval during early pregnancy by the ruminant embryonic trophectoderm, is essential for the maintenance of early pregnancy, but the mechanism by which it is transcriptionally regulated has not been fully determined. To identify a transcription factor(s) involved in the down-regulation of IFNT genes, mRNAs for various known transcription factors were investigated by reverse-transcriptase and real-time PCR in conceptus tissues collected on Days 15, 17, and 21, or Days 17, 20, and 22 of ovine or bovine pregnancy, respectively. In particular, the T-box protein eomesodermin (EOMES) exhibited high mRNA expression in Day 17 or 22 ovine or bovine conceptuses. Interaction between EOMES and the identified transcription factors was studied using transient transfection, revealing that ovine/bovine IFNT-reporter transactivation was down-regulated by EOMES. Transcription factor interactions with EOMES were further studied through immunoprecipitation, demonstrating an association between EOMES and cAMP-response element binding protein (CREB)-binding protein (CREBBP). Uterine flushing media collected from cyclic or early pregnancy animals were added to bovine trophoblast CT-1 cells cultured on type-I collagen (monoculture) or bovine uterine epithelial cells (coculture) in an attempt to regulate EOMES expression. In the coculture, but not the monoculture, addition of uterine flushing from Day 17 pregnant animals resulted in increased EOMES expression in CT-1 cells. These results suggest that as conceptuses attach to the uterine epithelium, IFNT gene transcription is down-regulated by an increase in EOMES expression and EOMES-CREBBP binding in the attached trophoblast cells.

Human placentation from nidation to 5 weeks of gestation. Part II: Tools to model the crucial first days

Human pregnancy is unusual with respect to monthly spontaneous decidualisation as well as the degree of placental invasion and interaction with the decidualised endometrial stroma. This review covers in vivo animal models and in vitro cell culture models that have been used to study the earliest stages of human implantation and placentation from nidation to 5 weeks of gestation. The field has expanded rapidly in recent years due to the generation of human embryonic stem cell lines and the ability of some scientists to culture human blastocysts. These models have enabled researchers to begin to elucidate the interactions involved in human blastocyst apposition, adhesion and implantation. However, we still understand very little about the differentiation processes involved in the formation of the placenta. Continued improvements to current models, including the potential isolation of a human trophoblast stem cell, will significantly enhance our ability to define the molecular and structural events occurring during human implantation and early placental 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.

Expression of mesenchymal-related genes by the bovine trophectoderm following conceptus attachment to the endometrial epithelium

In the course of experiments to identify and characterize the factors that function in bovine conceptuses during peri-attachment periods, various transcripts related to the epithelial-mesenchymal transition (EMT) were found. In this study, RNA was extracted from different sets of days 17, 20, and 22 (day 0=day of estrous) bovine conceptuses and subjected to real-time PCR analysis as well as Western blotting, from which abundances of N-cadherin (CDH2), vimentin, matrix metalloproteinase 2 (gelatinase A, 72 kDa gelatinase, 72 kDa type IV collagenase) (MMP2), and matrix metallopeptidase 9 (gelatinase B, 92 kDa gelatinase, 92 kDa type IV collagenase) (MMP9) mRNAs were determined on day 22, concurrent with (CDH1) mRNA and protein downregulation. Transcription factors in EMT processes were then analyzed and changes in snail homolog 2 (Drosophila) (SNAI), zinc finger E-box binding homeobox 1 (ZEB1), zinc finger E-box binding homeobox 2 (ZEB2), twist homolog 1 (Drosophila) (TWIST1), twist homolog 2 (Drosophila) (TWIST2), and Kruppel-like factor 8 (KLF8) transcripts were found in day 22 conceptuses, while confirming SNAI2 expression by Western blotting. Immunohistochemical analysis revealed that the day 22 trophectoderm expressed the mesenchymal markers N-cadherin and vimentin as well as the epithelial marker cytokeratin. In attempts to identify the molecular mechanisms by which the trophectoderm expressed EMT-related genes, growth factor receptors associated with EMT were analyzed. Upregulation of the growth factor receptor transcripts, fibroblast growth factor receptor 1 (FGFR1), platelet-derived growth factor receptor, alpha polypeptide (PDGFRA), platelet-derived growth factor receptor, beta polypeptide (PDGFRB), and transforming growth factor, beta receptor II (70/80 kDa) (TGFBR2) mRNAs, was found on day 22. The analysis was extended to determine the integrin (ITG) transcripts and found high levels of integrin, alpha 4 (antigen CD49D, alpha 4 subunit of VLA-4 receptor) (ITGA4), integrin, alpha 8 (ITGA8), integrin, beta 3 (platelet glycoprotein IIIa, antigen CD61) (ITGB3), and integrin, beta 5 (ITGB5) mRNAs on day 22. These observations indicate that after the conceptus-endometrium attachment, EMT-related transcripts as well as the epithelial marker cytokeratin were present in the bovine trophectoderm and suggest that the implantation process for noninvasive trophoblasts requires not only extracellular matrix expression but also partial EMT.

Expression of GATA1 in the ovine conceptus and endometrium during the peri-attachment period

The transcription factor GATA1 is known to play an essential role in hematopoiesis, but its other roles have not been well characterized. The purpose of this study was to determine relationships between GATA1 and GATA2 and/or GATA3, and to identify their possible functions in ovine development. GATA1 mRNA was found in ovine conceptuses and endometrial epithelial regions of Day 15 (Day 0=day of estrus) cyclic and Days 15, 17, and 21 pregnant ovine uteri. GATA1 mRNA was strongly expressed in conceptuses on Day 21, when trophoblast attachment to the maternal endometrium progressed. Similarly, GATA1 protein expression was relatively high on Day 21. To localize GATA1 mRNA, ovine conceptuses and pregnant uteri were subjected to in situ hybridization on Days 15, 17, and 21, confirming that GATA1 mRNA was expressed in trophoblasts and uterine endometrial epithelial cells in these gestation days. The presence of GATA1 protein was further confirmed by immunohistochemistry. Because high GATA1 expression appeared to coincide with reduced GATA2/3 expression, a potential role of GATA1 was examined through transfection of a mouse Gata1 expression plasmid into bovine trophoblast F3 cells. This over-expression resulted in the down-regulation of endogenous GATA2 transcripts. These observations indicate that GATA1 exists in the ovine conceptus and uterus during the peri-attachment period, and suggest that GATA1 is integral to conceptus and endometrial development through the regulation of GATA2 and possibly other developmentally important genes.

Regulation of trophoblast-specific factors by GATA2 and GATA3 in bovine trophoblast CT-1 cells

Numerous transcription factors that regulate trophoblast developmental processes have been identified; however, the regulation of trophoblast-specific gene expression has not been definitively characterized. While a new role of Gata3 in trophoblast development was being demonstrated in mice, we examined effects of GATA transcription factors on conceptus interferon tau (IFNT), a major trophectoderm factor in ruminants. In this study, expression patterns of trophoblast ASCL2, CDX2, CSH1, ELF5, HAND1, IFNT, and TKDP1 mRNAs were initially examined, from which ASCL2, CDX2, IFNT, and TKDP1 mRNAs were found to be similar to those of GATA2 and GATA3 in days 17, 20, and 22 (day 0=day of estrus) bovine conceptuses. A chromatin immunoprecipitation (ChIP) assay revealed that endogenous GATA2 and GATA3 occupied GATA binding sites on the upstream regions of CSH1, IFNT, and TKDP1 genes and on the intron 1 region of CDX2 gene in bovine trophoblast CT-1 cells. In transient transfection analyses of the upstream region of bovine CSH1, and IFNT or the intron 1 region of CDX2 gene, over-expression of GATA2 induced transactivation of these trophoblast-specific genes in bovine non-trophoblast ear fibroblast EF cells, but over-expression of GATA3 did not substantially affect their transactivation. In CT-1 cells, endogenous CDX2 and IFNT mRNAs were down-regulated by GATA2 siRNA, while endogenous ASCL2 and CDX2 mRNAs were down-regulated by GATA3 siRNA. Our results indicate that in addition to trophectoderm lineage specification, GATA2 and/or GATA3 are involved in the regulation of trophoblast-specific gene transcription in bovine trophoblast CT-1 cells.