Localization and binding of transforming growth factor-beta isoforms in mouse preimplantation embryos and in delayed and activated blastocysts

Mammalian embryo culture media: now and into the future

For over 70years, since the culture of the first mammalian embryo in vitro , scientists have undertaken studies to devise and optimise media to support the manipulation and culture of gametes and embryos. This area of research became especially active in the late 1970s onwards following the successful birth of the first human in vitro fertilised embryo. This review summarises some of the key advances in mammalian embryo culture media over time based on a greater understanding of the biochemical milieu of the reproductive tract. It highlights how learnings from studies in mice and agricultural species have informed human culture media compositions, in particular the inclusion of albumin, growth factors, cytokines, and antioxidants into contemporary culture media formulations, and how these advances may then in turn help to inform and guide development of in vitro culture systems used in other arenas, in particular agriculture. Additionally, it will highlight how the introduction of new technologies, such as timelapse, can influence current trends in media composition and usage that may see a return to a single step medium.

Maternal MicroRNA Profile Changes When LH Is Added to the Ovarian Stimulation Protocol: A Pilot Study

While the use of follicle-stimulating hormone (FSH) in ovarian stimulation for in vitro fertilization (IVF) is an established practice, the use of luteinizing hormone (LH) remains debatable. MicroRNAs (miRNAs) are short, endogenous, non-coding transcripts that control a variety of cellular functions, such as gonadotrophin production and follicular development. The goal of this pilot study was to investigate whether the employment of recombinant LH (rLH) in ovarian stimulation protocols results in changes in the miRNA profiles in human oocytes. Patients were divided into two groups: seven received recombinant FSH (rFSH, 225 IU), and six received rFSH (150 IU) plus rLH (75 IU). MiRNA predesigned panels and real-time PCR technology were used to analyze the oocytes retrieved from the follicular ovarian retrieval. Among the miRNAs evaluated, a series of them evidenced upregulation or downregulation in their expression in the FSH plus LH group compared to the FSH group. Considering the results obtained from the functional and network analysis, the different maternal miRNA profiles in the two groups revealed a differential modulation of pathways involved in numerous biological functions. Overall, based on the pathways associated with most of these maternal miRNAs, the presence of LH may result in a different modulation of pathways regulating survival under the control of a Tp53-related mechanism. Interestingly, among the miRNAs differentially expressed in oocytes of the two groups, we have found miRNAs already investigated at ovarian, follicular, oocyte, and embryonic levels: hsa-miR-484, hsa-miR-222, hsa-miR-520d-5p, hsa-miRNA-17, hsa-miR-548, and hsa-miR-140. Thus, investigation into the role of these miRNAs in oocyte molecular pathways may help determine how LH affects oocyte competence and eventually leads to the clinical improvement of IVF.

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.

Regulation of Embryonic Signal on Talin1 in Mouse Endometrium

Embryonic signals can affect the spatiotemporal-specific expression of the uterus to establish a successful pregnancy. Our previous study has found that talin1 underwent dynamic changes in the mouse endometrium during peri-implantation period. However, whether talin1 is affected by the embryo signals is not clear. In order to investigate the effect of embryonic signals, especially human chorionic gonadotropin (HCG) on talin1, we have designed mouse models of pseudopregnancy, delayed implantation and activation, and HCG treatment. Using these models, the expression of talin1 in the mouse endometrium was determined by immunohistochemistry and Western blotting. In the pseudopregnancy model, an increased expression of talin1 was found from day 3 to day 5, whereas the talin1 protein was decreased on day 5 in the normal pregnant mice. In the delayed implantation model, a strong cytoplasmic staining of talin1 was found, especially in stromal cells. However, after activation of the implantation, the expression of talin1 decreased (P < .05). Furthermore, a significantly lower expression of talin1 was found at the implantation site when compared to the interimplantation sites (P < .05). In the HCG treatment model, an intrauterine perfusion of 10u HCG significantly reduced the expression of talin1 in both stromal and epithelial cells in pseudopregnant mice (P < .05), although further increase in the HCG concentration did not have additional effect on expression of talin1. Taken together, our data suggest that the presence of embryos can affect expression of talin1 in the mouse endometrium, and a certain concentration of HCG can regulate its expression.

Dynamic Pattern of HOXB9 Protein Localization during Oocyte Maturation and Early Embryonic Development in Mammals

Background

We previously showed that the homeodomain transcription factor HOXB9 is expressed in mammalian oocytes and early embryos. However, a systematic and exhaustive study of the localization of the HOXB9 protein, and HOX proteins in general, during mammalian early embryonic development has so far never been performed.

Results

The distribution of HOXB9 proteins in oocytes and the early embryo was characterized by immunofluorescence from the immature oocyte stage to the peri-gastrulation period in both the mouse and the bovine. HOXB9 was detected at all studied stages with a dynamic expression pattern. Its distribution was well conserved between the two species until the blastocyst stage and was mainly nuclear. From that stage on, trophoblastic cells always showed a strong nuclear staining, while the inner cell mass and the derived cell lines showed important dynamic variations both in staining intensity and in intra-cellular localization. Indeed, HOXB9 appeared to be progressively downregulated in epiblast cells and only reappeared after gastrulation had well progressed. The protein was also detected in the primitive endoderm and its derivatives with a distinctive presence in apical vacuoles of mouse visceral endoderm cells.

Conclusions

Together, these results could suggest the existence of unsuspected functions for HOXB9 during early embryonic development in mammals.

Autocrine embryotropins revisited: how do embryos communicate with each other in vitro when cultured in groups?

In the absence of the maternal genital tract, preimplantation embryos can develop in vitro in culture medium where all communication with the oviduct or uterus is absent. In several mammalian species, it has been observed that embryos cultured in groups thrive better than those cultured singly. Here we argue that group-cultured embryos are able to promote their own development in vitro by the production of autocrine embryotropins that putatively serve as a communication tool. The concept of effective communication implies an origin, a signalling agent, and finally a recipient that is able to decode the message. We illustrate this concept by demonstrating that preimplantation embryos are able to secrete autocrine factors in several ways, including active secretion, passive outflow, or as messengers bound to a molecular vehicle or transported within extracellular vesicles. Likewise, we broaden the traditional view that inter-embryo communication is dictated mainly by growth factors, by discussing a wide range of other biochemical messengers including proteins, lipids, neurotransmitters, saccharides, and microRNAs, all of which can be exchanged among embryos cultured in a group. Finally, we describe how different classes of messenger molecules are decoded by the embryo and influence embryo development by triggering different pathways. When autocrine embryotropins such as insulin-like growth factor-I (IGF-I) or platelet activating factor (PAF) bind to their appropriate receptor, the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) pathway will be activated which is important for embryo survival. On the other hand, the mitogen-activated protein kinase (MAPK) pathway is activated when compounds such as hyaluronic acid and serotonin bind to their respective receptors, thereby acting as growth factors. By activating the peroxisome-proliferator-activated receptor family (PPAR) pathway, lipophilic autocrine factors such as prostaglandins or fatty acids have both survival and anti-apoptotic functions. In conclusion, considering different types of messenger molecules simultaneously will be crucial to understanding more comprehensively how embryos communicate with each other in group-culture systems. This approach will assist in the development of novel media for single-embryo culture.

Defining the three cell lineages of the human blastocyst by single-cell RNA-seq

Here, we provide fundamental insights into early human development by single-cell RNA-sequencing of human and mouse preimplantation embryos. We elucidate conserved transcriptional programs along with those that are human specific. Importantly, we validate our RNA-sequencing findings at the protein level, which further reveals differences in human and mouse embryo gene expression. For example, we identify several genes exclusively expressed in the human pluripotent epiblast, including the transcription factor KLF17. Key components of the TGF-β signalling pathway, including NODAL, GDF3, TGFBR1/ALK5, LEFTY1, SMAD2, SMAD4 and TDGF1, are also enriched in the human epiblast. Intriguingly, inhibition of TGF-β signalling abrogates NANOG expression in human epiblast cells, consistent with a requirement for this pathway in pluripotency. Although the key trophectoderm factors Id2, Elf5 and Eomes are exclusively localized to this lineage in the mouse, the human orthologues are either absent or expressed in alternative lineages. Importantly, we also identify genes with conserved expression dynamics, including Foxa2/FOXA2, which we show is restricted to the primitive endoderm in both human and mouse embryos. Comparison of the human epiblast to existing embryonic stem cells (hESCs) reveals conservation of pluripotency but also additional pathways more enriched in hESCs. Our analysis highlights significant differences in human preimplantation development compared with mouse and provides a molecular blueprint to understand human embryogenesis and its relationship to stem cells.

Summary: Single-cell RNA-sequencing of human and mouse embryos reveals conserved and human-specific transcriptional programmes as well as a functional requirement for TGFβ signalling in human embryos.

Deciphering the molecular basis of uterine receptivity

Uterine receptivity is defined as a limited time period during which the uterus enters into an appropriately differentiated state that is ready for the initiation of implantation by competent blastocysts. Although various cellular aspects and molecular pathways involved in uterine receptivity have been identified by gene expression studies and genetically engineered mouse models, a comprehensive understanding of the window of uterine receptivity is still missing. This review focuses on the recent progress in this area, with particular focus on the molecular basis of stromal-epithelial dialogue and crosstalk between the blastocyst and the uterus during implantation. A better understanding of the underlying mechanisms governing the window of uterine receptivity is hoped to generate new strategies to correct implantation failure and to improve pregnancy rates in women.

Involvement of microRNA lethal-7a in the regulation of embryo implantation in mice

MicroRNAs interact with multiple mRNAs resulting in their degradation and/or translational repression. This report used the delayed implantation model to determine the role of miRNAs in blastocysts. Dormant blastocysts in delayed implanting mice were activated by estradiol. Differential expression of 45 out of 238 miRNAs examined was found between the dormant and the activated blastocysts. Five of the nine members of the microRNA lethal-7 (let-7) family were down-regulated after activation. Human blastocysts also had a low expression of let-7 family. Forced-expression of a family member, let-7a in mouse blastocysts decreased the number of implantation sites (let-7a: 1.1±0.4; control: 3.8±0.4) in vivo, and reduced the percentages of blastocyst that attached (let-7a: 42.0±8.3%; control: 79.0±5.1%) and spreaded (let-7a: 33.5±2.9%; control: 67.3±3.8%) on fibronectin in vitro. Integrin-β3, a known implantation-related molecule, was demonstrated to be a target of let-7a by 3′-untranslated region reporter assay in cervical cancer cells HeLa, and Western blotting in mouse blastocysts. The inhibitory effect of forced-expression of let-7a on blastocyst attachment and outgrowth was partially nullified in vitro and in vivo by forced-expression of integrin-β3. This study provides the first direct evidence that let-7a is involved in regulating the implantation process partly via modulation of the expression of integrin-β3. (200 words).

Accelerated re-epithelialization in Dpr2-deficient mice is associated with enhanced response to TGFβ signaling

Members of the Dapper (Dpr)/Dact protein family are involved in the regulation of distinct signaling pathways, including TGFβ/Nodal, canonical and noncanonical Wnt pathways. Three Dpr genes, Dpr1, Dpr2 and Dpr3, are expressed in mouse embryos and in many adult tissues; however, their in vivo functions have not been reported. In this study, we generated Dpr2-deficient mice using a gene-knockout approach. Homozygous Dpr2 knockout (Dpr2–/–) embryos developed normally and postnatal Dpr2–/– mice grew to adulthood without obvious morphological or behavioral defects. We found that Dpr2 was expressed highly in epidermal keratinocytes and in hair follicles of adult mice, and that Dpr2 deficiency resulted in accelerated re-epithelialization during cutaneous wound healing. Furthermore, we demonstrated that loss of Dpr2 function enhanced the responses of keratinocytes to TGFβ stimulation, and that TGFβ signals promoted adhesion to fibronectin and migration of keratinocytes, by regulating the expression of specific integrin genes. Thus, Dpr2 plays an inhibitory role in the re-epithelialization of adult skin wounds by attenuating TGFβ signaling.

Null mutation in transforming growth factor beta1 disrupts ovarian function and causes oocyte incompetence and early embryo arrest

TGFbeta1 is implicated in regulation of ovarian function and the events of early pregnancy. We have investigated the effect of null mutation in the Tgfbeta1 gene on reproductive function in female mice. The reproductive capacity of TGFbeta1 null mutant females was severely impaired, leading to almost complete infertility. Onset of sexual maturity was delayed, after which ovarian function was disrupted, with extended ovarian cycles, irregular ovulation, and a 40% reduction in oocytes ovulated. Serum FSH and estrogen content were normal, but TGFbeta1 null mutant mice failed to display the characteristic proestrus surge in circulating LH. Ovarian hyperstimulation with exogenous gonadotropins elicited normal ovulation rates in TGFbeta1 null mutant mice. After mating with wild-type stud males, serum progesterone content was reduced by 75% associated with altered ovarian expression of mRNAs encoding steroidogenic enzymes 3beta-hydroxysteroid dehydrogenase-1 and P450 17 alpha-hydroxylase/C17-20-lyase. Embryos recovered from TGFbeta1 null mutant females were developmentally arrested in the morula stage and rarely progressed to blastocysts. Attempts to rescue embryos by exogenous progesterone administration and in vitro culture were unsuccessful, and in vitro fertilization and culture experiments demonstrated that impaired development is unlikely to result from lack of maternal tract TGFbeta1. We conclude that embryo arrest is due to developmental incompetence in oocytes developed in a TGFbeta1-deficient follicular environment. This study demonstrates that TGFbeta1 is a critical determinant of normal ovarian function, operating through regulation of LH activity and generation of oocytes competent for embryonic development and successful initiation of pregnancy.

Temporal and spatial expression of TGF-beta2 in chicken somites during early embryonic development

A multifunctional growth and differentiation factor TGF-beta is expressed at various developmental stages, and its principle role may be involvement in organogenesis. The present study was performed to evaluate the temporal and spatial expression of TGF-beta2 mRNA in developing somites of chicken embryos during their early developmental periods. TGF-betas were expressed in various tissues of the whole embryo obtained at stage 26 (5 days of incubation) as revealed by whole-mount in situ hybridization. TGF-beta2 mRNA was predominantly expressed in somites as well as the head, branchial arch, wing buds, and leg buds. TGF-beta2 mRNA first appeared in the rostral somites on E4, and its expression sites expanded to the middle range of somites at stage 26. At stages 29-31 (6-7 days), expression in the rostral somites disappeared, and it appeared in the caudal somites. TGF-beta2 expression was also analyzed in sections of the embryo by in situ hybridization. The expression sites of TGF-beta2 were clearly observed in the myotomal somite tips as well as the neural tube. RT-PCR analysis showed that TGF-beta2 expression was very low in the blastocyte stage embryo and thereafter increased linearly in the whole trunk until stage 26. These data indicate that TGF-beta2 may be a regulatory factor participating in the somitogenesis of chicken embryos.

TGFbeta/activin/nodal signaling is necessary for the maintenance of pluripotency in human embryonic stem cells

Human embryonic stem cells (hESCs) self-renew indefinitely and give rise to derivatives of all three primary germ layers, yet little is known about the signaling cascades that govern their pluripotent character. Because it plays a prominent role in the early cell fate decisions of embryonic development, we have examined the role of TGFbeta superfamily signaling in hESCs. We found that, in undifferentiated cells, the TGFbeta/activin/nodal branch is activated (through the signal transducer SMAD2/3) while the BMP/GDF branch (SMAD1/5) is only active in isolated mitotic cells. Upon early differentiation, SMAD2/3 signaling is decreased while SMAD1/5 signaling is activated. We next tested the functional role of TGFbeta/activin/nodal signaling in hESCs and found that it is required for the maintenance of markers of the undifferentiated state. We extend these findings to show that SMAD2/3 activation is required downstream of WNT signaling, which we have previously shown to be sufficient to maintain the undifferentiated state of hESCs. Strikingly, we show that in ex vivo mouse blastocyst cultures, SMAD2/3 signaling is also required to maintain the inner cell mass (from which stem cells are derived). These data reveal a crucial role for TGFbeta signaling in the earliest stages of cell fate determination and demonstrate an interconnection between TGFbeta and WNT signaling in these contexts.

Unique and selective effects of five Ets family members, Elf3, Ets1, Ets2, PEA3, and PU.1, on the promoter of the type II transforming growth factor-beta receptor gene

Previous studies have shown that the promoter of the type II TGF-beta receptor gene (TbetaR-II) is strongly stimulated by Elf3, a member of the Ets transcription factor family. The TbetaR-II gene behaves as a tumor suppressor and it is expressed in nearly all cell types, whereas Elf3 is expressed primarily in epithelial cells. Hence, the TbetaR-II gene is likely to be regulated by other Ets proteins in nonepithelial cells. In this study, we examined the effects of four other Ets family members (Ets1, Ets2, PEA3, and PU.1) on TbetaR-II promoter/reporter constructs that contain the two essential ets sites of this gene. These studies employed F9 embryonal carcinoma cells and their differentiated cells, because transcription of the TbetaR-II gene increases after F9 cells differentiate. Here we demonstrate that Ets2, which is expressed in F9-differentiated cells along with Elf3, does not stimulate or bind to the TbetaR-II promoter in these cells. In contrast, PEA3 stimulates the TbetaR-II promoter in F9-differentiated cells, but it inhibits this promoter in F9 cells. Thus, the effects of PEA3 on the TbetaR-II promoter are cell context-dependent. We also show that the effects of Elf3 are cell context-dependent. Elf3 strongly stimulates the TbetaR-II promoter in F9-differentiated cells, but not in F9 cells. In contrast to Elf3 and PEA3, Ets1 strongly stimulates this promoter in both F9 cells and F9-differentiated cells. Finally, we show that PU.1 exerts little or no effect on the activity of the TbetaR-II promoter. Together, our findings indicate that Elf3 is not the only Ets protein capable of stimulating the TbetaR-II promoter. Importantly, our findings also indicate that each of the five Ets proteins influences the TbetaR-II promoter in a unique manner because of important differences in their biochemical properties or their patterns of cellular expression.

Embryonic signals direct the formation of tight junctional permeability barrier in the decidualizing stroma during embryo implantation

The protection of the embryo from the maternal adverse environment during early pregnancy is considered to be achieved by the establishment of a transitory permeability barrier created by decidual cells immediately surrounding the implanting embryo. Normally, the polarized epithelium acts as a barrier by regulating paracellular passage of substances through tight junctions. The expression of tight junction proteins in the uterine luminal epithelium prior to implantation is consistent with this idea. However, limited information is available regarding the nature and regulation of the permeability barrier that is created by decidualizing stromal cells during implantation. We show here that the tight junction proteins, occludin, claudin-1, zonula occludens-1 and zonula occludens-2, are all expressed and physically associated in decidualizing stromal cells of the primary decidual zone forming a barrier surrounding the embryo with the loss of adjacent luminal epithelium. The blastocyst trophectoderm appears to be the stimulus for the creation of this barrier, since isolated inner cell mass or artificial stimuli failed to induce such a barrier. Furthermore, the primary decidual zone induced by the normal blastocyst is impermeable to immunoglobulin molecules. These findings suggest that trophoblast-induced expression of tight junctions forms a temporary barrier in cells of the primary decidual zone that restricts the passage of injurious stimuli such as maternal immunoglobulins to the embryo.

Comparison of oocyte factors and transforming growth factor-beta in the regulation of DNA synthesis in bovine granulosa cells

Oocytes are powerful local modulators of follicular cell functions and many of the activities of oocytes are attributed to members of the transforming growth factor-beta (TGF-beta) superfamily. Whilst in the mouse it is known that members of this family are able to mimic many of the effects of oocytes on follicular cells, the relative importance of any of these factors is unknown in bovine follicles. The objectives of this study were to determine if bovine oocytes express and secrete TGF-beta and to compare oocyte-secreted factor(s) to TGF-beta in terms of their capacities to stimulate mural granulosa cell (MGC) DNA synthesis. Bovine ovaries were collected from an abattoir and RNA was extracted from isolated MGC, cumulus cells, cumulus-oocyte complexes and denuded oocytes (DO). Using RT-PCR, all cell types were found to express TGF-beta1 and TGF-beta2 mRNA transcripts. However, no TGF-beta bioactivity could be detected from DO using a sensitive (40 pg/ml) and specific mink lung fibroblast cell bioassay. MGC were cultured with various combinations and doses of TGF-beta2 and DO for 18 h, followed by a 6-h pulse of [3H]-thymidine as an indicator of cellular DNA synthesis. MGC DNA synthesis was stimulated by both TGF-beta2 and DO. However in response to increasing doses of TGF-beta2, [3H]-thymidine levels plateaued at <2-fold above control levels, whereas levels continued to increase over the dose range of DO tested (up to 3.4-fold). Addition of a TGF-beta pan-specific neutralising antibody to MGC cultures eliminated the TGF-beta2-stimulatory effects on DNA synthesis and the TGF-beta2-suppressive effects on progesterone production, but the antibody was unable to neutralise the same responses when induced by DO. These results support a role for TGF-beta1, TGF-beta2 and DO in paracrine/autocrine regulation of bovine granulosa cell function, but indicate that neither TGF-beta1 nor TGF-beta2 can account for the actions of bovine oocytes on granulosa cells.

Embryos sired by males without accessory sex glands induce failure of uterine support: a study of VEGF, MMP and TGF expression in the golden hamster

To account for reproductive failure induced by surgical deletion of paternal accessory sex glands in the golden hamster in vivo, we studied expression of vegf, FLT-1 (VEGF-R1), FLK-1 (VEGF-R2), MMP and TGF-beta in endometrium of the dam and sired embryos during 5-7 days post coitum by immunohistochemistry, in situ hybridisation, semiquantitative RT-PCR and enzyme-linked immunosorbent assay. Spatiotemporal pattern of vegf expression in the control animals was similar to that reported for intact animals by our group. Removal of paternal ampullary glands did not disturb the normal expression pattern. Removal of ventral prostate glands alone or all accessory sex glands was associated with reduction of vegf transcripts and protein levels in both the embryo and endometrium. FLT-1, FLK-1 and MMP-2 were also reduced. MMP-1 was not changed whereas TGF-beta1 expression was enhanced. There was no expression in endometrium in between implantation sites. Thus the implanted embryos had a trophic effect on growth factor production by the endometrium, and the levels of expression were determined by viability and structural integrity of the conceptus. Based on these findings we concluded that incompetent embryos sired by males without the ventral prostate gland or all accessory sex glands reduced the potential of the uterus to support pregnancy. A negative cycle of events was thus set up and eventually led to premature termination of pregnancies.

Defining the actions of transforming growth factor beta in reproduction

Members of the transforming growth factor beta (TGFbeta) family are pleiotropic cytokines with key roles in tissue morphogenesis and growth. TGFbeta1, TGFbeta2 and TGFbeta3 are abundant in mammalian reproductive tissues, where development and cyclic remodelling continue in post-natal and adult life. Potential roles for TGFbeta have been identified in gonad and secondary sex organ development, spermatogenesis and ovarian function, immunoregulation of pregnancy, embryo implantation and placental development. However, better tools must now be employed to map more precisely essential functions and the regulatory networks governing their activity. Gene ablation and transgenic models are expected to provide novel insights into distinct physiological activities for each TGFbeta isoform in normal reproductive function and reproductive pathologies. It is also necessary to consider the mechanisms controlling TGFbeta activation from latent precursor forms, and receptor and binding protein expression. Smad intracellular signalling circuitry and modulation by environmental stimuli through cross-talk with other signal transduction pathways will further constrain TGFbeta action. This review examines existing evidence for TGFbeta1, TGFbeta2 and TGFbeta3 regulation of male and female reproductive biology, and highlights prospects for future research.

The influence of growth factors on the development of preimplantation mammalian embryos

The development of the preimplantation mammalian embryo from a fertilized egg to a blastocyst capable of implanting in the uterus is a complex process. Cell division must be carefully programmed. The embryonic genome must be activated at the appropriate stage of development, and the pattern of gene expression must be carefully coordinated for the initiation of the correct program of differentiation. Cell fates must be chosen to establish specific cell types such as the inner cell mass and the trophectoderm, which give rise to the embryo proper and the placenta, respectively. This review summarizes recent findings concerning the influence of growth factors on the development of preimplantation mammalian embryos. Maternal factors secreted into the lumen of the female reproductive tract as well as substances synthesized by the developing embryo itself help to regulate this process. Studies of embryos in culture and investigations using homologous recombination to create embryos and animals null for specific genes have enabled the identification of several growth factors that appear essential for preimplantation mammalian embryo development. Some of the factors are required maternal factors; others are embryo-derived autocrine and paracrine factors. Studies using molecular biology are beginning to identify differences in the patterns of genes expressed by naturally derived embryos and those developing in culture. The knowledge gained from studies on growth factors, media, embryonic development, and gene expression should help improve culture conditions for embryos and will provide for safer outcomes from assisted reproductive procedures in human and animal clinics.

Immunohistochemical expression of Smads 1-6 in the 15-day gestation mouse embryo: signaling by BMPs and TGF-betas

The eight mammalian Smad proteins mediate cellular signaling from members of the transforming growth factor-beta (TGF-beta), bone morphogenetic protein (BMP), and activin families. Smads 1, 5, and 8 transmit signals from BMPs, while Smads 2 and 3 transmit signals from TGF-betas and activin. Smad 4 is a common mediator of both pathways, while Smads 6 and 7 inhibit signaling. Signal transduction involves translocation of Smad complexes to the nucleus and subsequent gene activation. Little is known about the expression of endogenous Smad proteins during development. We identified commercially available Smad antibodies that specifically recognize a unique Smad protein and are suitable for immunohistochemistry. Here we compare the localization of Smads 1, 2, 3, 4, 5, and 6 in tissues of the 15-day gestation mouse embryo. Immunoreactive Smad proteins are seen in many tissues with differences in the localization being dependent upon the cell type. All tissues express Smad 4 and at least one each of the BMP-specific and TGF-beta-specific Smads, while expression of Smad 6 is more restricted. Differences are observed in the nuclear versus cytoplasmic localization among the Smads in different cell types or tissues, suggesting selective activation of Smads during this stage of development.

The expression and structure of TGF-beta2 transcripts in rat muscles

The transforming growth factor-beta2 (TGF-beta2) transcripts expressed in various tissues of rat were characterised by RT-PCR and the nucleotide sequence of the cDNAs determined. A transcript with an 84-nucleotide insert in the latency-associated peptide region, the long form, was found. The long form of TGF-beta2 was detected in the aorta, primary bronchus, uterus, heart, skeletal muscle, sciatic nerve and spinal cord but not in the intestine. The 3' untranslated region of TGF-beta2 contained several putative AU-rich elements and multiple polyadenylation sites, indicating post-transcriptional regulation of TGF-beta2 synthesis. The levels of TGF-beta2 transcripts were estimated using semi-quantitative RT-PCR. They were down-regulated during muscle development and up-regulated after denervation. The long form constituted approximately 6% of the total TGF-beta2 messages in skeletal muscle.

Blastocyst H(2) receptor is the target for uterine histamine in implantation in the mouse

The process of implantation is a ‘two-way’ interaction between the blastocyst and uterus. It has long been suspected that histamine is an important mediator in embryo-uterine interactions during implantation, but its source, targets and mechanism of actions remained undefined. We have recently demonstrated that uterine epithelial cells are the source of histamine, which peaks on day 4 of pregnancy (the day of implantation) in the mouse. In searching for its target and site of action, we discovered that preimplantation blastocysts, which express histamine type 2 receptor (H(2)), is the target for histamine action. Using multiple approaches, we demonstrate herein that uterine-derived histamine interacts with embryonic H(2) receptors in a paracrine fashion to initiate the process of implantation.

Expression and regulation of vascular endothelial growth factor in a first trimester trophoblast cell line

Embryo implantation and development are critically dependent upon the spatial and temporal regulation of angiogenesis and localized vascular permeability. A key mediator of these effects is the endothelial cell mitogen vascular endothelial growth factor (VEGF). VEGF has been shown to promote endometrial vascular permeability, fetal vasculogenesis and placental, fetal and maternal angiogenesis. However, the mechanism through which this regulation occurs in the placenta is poorly understood. This study was conducted to determine if the pro-angiogenic cytokines, TNF-alpha and TGF-beta1, affect VEGF expression in human first trimester trophoblasts. Culture of a first trimester trophoblast cell line (HTR-8/SVneo), in the presence of either TNF-alpha or TGF-beta1, resulted in the expression of significant levels of VEGF in culture. The trophoblast cell line also showed a time-dependent and a dose-dependent increase in VEGF mRNA levels when cultured in the presence of either TNF-alpha or TGF-beta1. These results suggest that both TNF-alpha and TGF-beta1 may regulate the production of VEGF in early gestational trophoblasts and may therefore serve to modulate placental vascular permeability and angiogenesis that are necessary for embryo implantation and placentation.

Treatment with all-trans-retinoic acid decreases levels of endogenous TGF-beta(1) in the mesenchyme of the developing mouse inner ear

BACKGROUND

Previous studies have shown that in utero exposure of the mouse embryo to high doses of all-trans-retinoic acid (atRA) produces defects of the developing inner ear and its surrounding cartilaginous capsule, while exposure of cultured periotic mesenchyme plus otic epithelium to high doses of exogenous atRA results in an inhibition of otic capsule chondrogenesis.

METHODS

In this study, we examine the effects of atRA exposure on the endogenous expression of transforming growth factor-beta(1) (TGF-beta(1)), a signaling molecule that mediates the epithelial-mesenchymal interactions that guide the development of the capsule of the inner ear.

RESULTS

Our results demonstrate a marked reduction in immunostaining for TGF-beta(1) in the periotic mesenchyme of atRA-exposed embryos of age E10.5 and E12 days in comparison with control specimens. Consistent with these in vivo findings, high-density cultures of E10.5 periotic mesenchyme plus otic epithelium, treated with doses of atRA that suppress chondrogenesis, showed significantly decreased levels of TGF-beta(1), as compared with TGF-beta(1) levels in untreated control cultures. Furthermore, we demonstrate a rescue of cultured periotic mesenchyme plus otic epithelium from atRA-induced chondrogenic suppression by supplementation of cultures with excess TGF-beta(1).

CONCLUSIONS

Our results support the hypothesis that TGF-beta(1) plays a role in mechanisms of atRA teratogenicity during inner ear development.

Strain dependency of TGFbeta1 function during embryogenesis

There is incomplete penetrance to Tgfb1 knockout phenotypes. About 50% of Tgfb1 homozygous mutant (Tgfb1-/-) and 25% of Tgfb1 heterozygous (Tgfb1+/-) embryos die during embryogenesis. In a mixed NIH/Ola x C57BL/6J/Ola x 129 background partial embryonic lethality of the Tgfb1-/-embryos occurs due to defective yolk sac vasculopoiesis and/or hematopoiesis. We show here that on a predominantly CF-1 genetic background, lack of TGFbeta1 causes a pre-morula lethality in about 50% of the null embryos. This partial lethality is not reversed by transfer of Tgfb1-/- embryos to Tgfb1-/+ hosts. The extent of embryonic lethality in Tgfb1-/- embryos ranges in a background dependent manner from 20% to 100%. Based on these and other studies it is clear that TGFbeta1 acts at two distinct phases of embryogenesis: pre-implantation development and yolk sac vasculogenesis/hematopoiesis. The susceptibility for the pre-implantation lethality depends on a small number of genetic modifiers since a small number of backcrosses onto the high susceptibility strain C57BL/6 leads to complete penetrance of the lethality.

erbB genes in the mouse uterus: cell-specific signaling by epidermal growth factor (EGF) family of growth factors during implantation

We previously described spatiotemporal expression of various epidermal growth factor (EGF)-like ligands and receptor subtypes, ErbB1 and ErbB2, during the peri-implantation period. To better understand the roles of these ligands and their possible signaling schemes in implantation, it is important to define the status of all the ligands and receptor subtypes in the uterus/embryo. No information is available about uterine and embryonic status of ErbB3 or ErbB4 during implantation. We cloned mouse erbB3 and erbB4 cDNAs and examined their expression and bioactivity in the peri-implantation uterus (days 1-8). Two erbB3 (cytoplasmic and extracellular) and three erbB4 (two cytoplasmic and one extracellular) clones were generated. Both forms of the erbB3 clone showed similar transcript profiles, while different transcript profiles were obtained with erbB4 clones. The steady-state levels of erbB3 and erbB4 mRNAs in whole uterine poly(A)+ RNA samples showed little changes during the peri-implantation period, while their unique cell-specific accumulation was noted. erbB3 is predominantly expressed in the epithelial cells, although decidual and embryonic cells also accumulate this mRNA. In contrast, the erbB4 mRNA is primarily expressed in the submyometrial stroma and myometrial connective tissues during this period. Additionally, the extracellular form of the erbB4 clone detected signals in a subpopulation of stromal cells. Autophosphorylation and immunoprecipitation studies provided evidence that uterine ErbB3 and ErbB4 are biologically active. This study provides a comprehensive analysis of possible ligand-receptor signaling schemes for EGF-like ligands in implantation.

Identification of two distinct functions for TGF-beta in early mouse development

In this study the function of transforming growth factor-beta (TGF-beta) in preimplantation mouse embryos was examined. By RT-PCR, mRNA for the signalling type I (T beta R-I) and type II (T beta R-II) receptors for TGF-beta was shown to be present in two distinct time windows: in fertilized oocytes and at the blastocyst stage. The function of TGF-beta at these times was analysed in two ways. Firstly, the TGF-beta signalling pathway was blocked by injecting a DNA construct encoding a truncated T beta R-II, that acts as a dominant-negative receptor, in fertilized oocytes, and the effect on development was determined. Secondly, inner cell masses isolated at the blastocyst stage were cultured in vitro with and without TGF-beta under conditions that favour the outgrowth of parietal endoderm. The results show that TGF-beta signalling mediated by maternally expressed receptors is important for development of preimplantation embryos beyond the two-cell stage, and suggest a regulatory role for TGF-beta in the outgrowth of parietal endoderm.

Cytokines in implantation

Implantation is a complex process which involves the 'invasion' of the maternal endometrium by the trophoblast surrounding the developing blastocyst. In response to this interaction there is a cellular reaction within the endometrium which has some features analogous to invasion by a tumour and some which are more characteristic of an inflammatory response. In addition, and also in common with cancer and inflammation, there is a release of biologically active molecules, including cytokines, at and around the implantation site. The information on cytokines is complex and often contradictory but it is recognised that they play an important role in the successful establishment of pregnancy. The evidence for this role is examined in this review.

Transcriptional activation of the type II transforming growth factor-beta receptor gene upon differentiation of embryonal carcinoma cells

Previously, it has been shown that differentiation of embryonal carcinoma (EC) cells turns on the expression of functional transforming growth factor type-beta receptors. Here, we show that the type II receptor (TbetaR-II) gene is activated at the transcriptional level when EC cells differentiate. We show that the differentiated cells, but not the parental EC cells, express transcripts for TbetaR-II. In addition, the expression of TbetaR-II promoter/reporter gene constructs are elevated dramatically when EC cells differentiate and we identify at least two positive and two negative regulatory regions in the 5' flanking region of the TbetaR-II gene. Moreover, we identify a cAMP response element/activating transcription factor site that acts as a positive cis-regulatory element in the TbetaR-II promoter, and we demonstrate that the transcription factor ATF-1 binds to this site and strongly stimulates the expression of the TbetaR-II promoter/reporter gene constructs when ATF-1 is overexpressed in EC-derived differentiated cells. Equally important, we identify a negative regulatory element in a 53-base pair region that had previously been shown to inhibit strongly the expression of TbetaR-II promoter/reporter gene constructs. Specifically, we demonstrate that this region, which contains an inverted CCAAT box motif, binds the transcription factor complex NF-Y (also referred to as CBF) in vitro. Furthermore, expression of a dominant-negative NF-YA mutant protein, which prevents DNA binding by NF-Y, enhances TbetaR-II promoter expression. Together, these studies suggest that the transcription factors ATF-1 and NF-Y play important roles in the regulation of the TbetaR-II gene.

TGFbeta2 knockout mice have multiple developmental defects that are non-overlapping with other TGFbeta knockout phenotypes

The growth and differentiation factor transforming growth factor-beta2 (TGFbeta2) is thought to play important roles in multiple developmental processes. Targeted disruption of the TGFbeta2 gene was undertaken to determine its essential role in vivo. TGFbeta2-null mice exhibit perinatal mortality and a wide range of developmental defects for a single gene disruption. These include cardiac, lung, craniofacial, limb, spinal column, eye, inner ear and urogenital defects. The developmental processes most commonly involved in the affected tissues include epithelial-mesenchymal interactions, cell growth, extracellular matrix production and tissue remodeling. In addition, many affected tissues have neural crest-derived components and simulate neural crest deficiencies. There is no phenotypic overlap with TGFbeta1- and TGFbeta3-null mice indicating numerous non-compensated functions between the TGFbeta isoforms.

Expression of heparan sulfate proteoglycan (perlecan) in the mouse blastocyst is regulated during normal and delayed implantation

Previous studies have shown that expression of the heparan sulfate proteoglycan, perlecan, on the external trophectodermal cell surfaces of mouse blastocysts increases during acquisition of attachment competence. However, it is not clear if this change in perlecan protein expression also is reflected at the level of perlecan mRNA expression. In the present investigation, the spatial and temporal patterns of perlecan mRNA expression in the mouse embryo during the periimplantation period were examined by in situ hybridization and reverse transcriptase-polymerase chain reaction. In addition, a delayed implantation model was used to determine the expression of perlecan mRNA and protein in dormant and estrogen-activated hatched blastocysts. The results demonstrate that perlecan mRNA expression is low in morulae, but increases in Day 4 blastocysts, attaining maximal expression in Day 4.5 attachment-competent blastocysts. In contrast, perlecan mRNA is detected in both the dormant and estrogen-activated delayed blastocysts; however, within 12 hr of blastocyst activation by estrogen, both perlecan protein and heparan sulfate chain expression markedly increase. Taken together, these results suggest that during normal development perlecan mRNA expression increases with the acquisition of attachment competence. Moreover, perlecan protein expression also is attenuated during delayed implantation and appears to increase in response to nidatory estrogen, perhaps via the increased translation of preexisting perlecan mRNA.

Transcriptional regulation of the TGF-beta 2 gene in choriocarcinoma cells and breast carcinoma cells: differential utilization of Cis-regulatory elements

Previous studies have shown that the transcription of the TGF-beta 2 gene is controlled by at least one negative and two positive regulatory regions in differentiated cells derived from both embryonal carcinoma cells and embryonic stem cells. The use of TGF-beta 2 promoter/reporter gene constructs has also identified a CRE/ATF motif near the TATA box that appears to heavily influence the transcription of the TGF-beta 2 gene. In this study, two choriocarcinoma cell lines, JAR and JEG-3, and the breast cancer cell line, MCF-7, were used to determine whether differences exist in the transcriptional regulation of the TGF-beta 2 gene. We demonstrated that both similarities and differences exist in the transcriptional regulation of this gene. Common to all cells examined to date, the positive regulatory region just upstream of the TATA box contains an essential CRE/ATF motif that binds at least one transcription factor, ATF-1, in gel mobility shift assays. However, we did not detect ATF-2 binding to this site with any of the nuclear extracts used. We also determined that the effect of the region between -187 and -78 (relative to the transcription start site) is cell type dependent. Previous studies have shown that this region acts to reduce the activity of the TGF-beta 2 promoter in differentiated cells derived from embryonal carcinoma cells and embryonic stem cells. In direct contrast, this region acts as a strong positive regulatory region in JAR, JEC-3, and MCF-7 cells. The mechanisms responsible for these differing effects remain to be established. Interestingly, this region does not appear to contain sequence motifs that bind known transcription factors. Thus, this region is likely to bind one or more novel transcription factors or contain novel recognition sites for known transcription factors.

Evidence for the involvement of transforming growth factor-alpha in implantation in the rat

This study was conducted to examine the possibility for participation of transforming growth factor-alpha (TGF-alpha), one of the epidermal growth factor (EGF) family of growth factors, in implantation in the rat. Immunostaining of TGF-alpha in the periimplantation uterus showed distinct staining in the luminal and glandular epithelium and moderate staining in stromal and myometrial cells. After implantation decidual cells and embryos were also positive stained for immunostaining. Immunocytochemistry of EGF receptor showed distinct staining in the luminal and glandular epithelium during the preimplantation period, and after implantation decidua at implantation sites and embryos were stained. Intraluminal injection of anti-TGF-alpha antibodies into uterine horns at 0600 h on day 5 of pregnancy decreased the number of rats showing implantation (blue dye reaction) at 0200 h on day 6 in a dose-dependent manner. Intraluminal injection of 100 pg of TGF-alpha on day 5 of pseudopregnancy elicited a greater decidual response when compared with the vehicle-injected contralateral uterine horn. Intraluminal injection of 20 pg of TGF-alpha into each uterine horn induced implantation in 50% of the ovariectomized progesterone-treated delayed implanting rats. These results suggest that TGF-alpha is involved in the implantation process in the rat.

Immunolocalization of estrogen receptor protein in the mouse blastocyst during normal and delayed implantation

We previously showed that estrogen receptor (ER) mRNA is present in preimplantation mouse embryos. The apparent synthesis of ER mRNA by the blastocyst at the time of implantation when estrogen is required was of special interest. A demonstration of the presence of ER protein would support the idea that estrogen can act directly on the embryo. The mouse embryo at the blastocyst stage is differentiated into two cell types, the trophectoderm and the inner cell mass. To determine whether ER mRNA is translated into ER protein and its cell-specific distribution, immunocytochemical analyses were performed in mouse blastocysts. ER protein was detected in all cell types of the normal, dormant, or activated blastocyst. To trace the fate of ER in these cell types, immunocytochemistry was performed in implanting blastocysts and early egg cylinder stage embryos developed in culture. Again, ER was detected in all cells of the implanting blastocyst. At the early egg cylinder stage, continued expression of ER was observed in cells derived from the inner cell mass or the trophoblast. In trophoblast giant cells, ER was concentrated in small regions of the nucleus, possibly the nucleoli, which was similar to that observed in dormant and activated blastocysts. The embryonic expression of ER at such early stages in a broad array of cells suggests that ER may have a general role during early development.

A phorbol ester that activates protein kinase C mimics the action of estradiol or epidermal growth factor for initiating embryo implantation in the delayed implanting hypophysectomized rat

In rodents an action of estrogen is required for the initiation of implantation of the blastocyst into the endometrium of a progesterone-primed uterus. Thus removal of endogenous estrogen, either directly by ovariectomy or indirectly by hypophysectomy, prevents implantation in the pregnant rat. In the present study, delayed implanting hypophysectomized progesterone-primed rats were used to test the efficacy of cyclic adenosine 3',5'-monophosphate (cAMP), epidermal growth factor (EGF) and insulin-like growth factor-I (IGF-I), which are agents that have been shown to mimic some uterine actions of estradiol, to initiate implantation. In confirmation of previous studies, EGF injected into the uterine lumen plus intravenously was effective at initiating implantation in all animals. IGF-I showed no such activity in this model system. Cyclic AMP, increased via direct activation of adenylyl cyclase by forskolin, or administration of sodium dibutyryl cAMP, did not initiate implantation. However, a ligand for protein kinase C (PKC), phorbol 12-myristate 13-acetate, was effective in augmenting the action of intrauterine EGF, or forskolin, for initiation of implantation. A phorbol ester that does not activate PKC was ineffective. The results provide circumstantial evidence for the requirement of PKC activity in the implantation initiating action of estrogens.

Defective haematopoiesis and vasculogenesis in transforming growth factor-beta 1 knock out mice

Transforming growth factor beta 1 (TGF beta 1) is shown here to be required for yolk sac haematopoiesis and endothelial differentiation. Mice with a targeted mutation in the TGF beta 1 gene were examined to determine the cause of prenatal lethality, which occurs in 50% of homozygous TGF beta 1 null (TGF beta 1−/−) conceptions. 50% of TGF beta 1−/− and 25% of TGF beta 1-+-) conceptions. 50% of TGF beta 1−/− and 25% of TGF beta 1+/− conceptuses were found to die at around 10.5 dpc. The primary defects were restricted to extraembryonic tissues, namely the yolk sac vasculature and haematopoietic system. The embryos per se showed developmental retardation, oedema and necrosis, which were probably secondary to the extraembryonic lesions. The defect in vasculogenesis appeared to affect endothelial differentiation, rather than the initial appearance and outgrowth of endothelial cells. Initial differentiation of yolk sac mesoderm to endothelial cells occurred, but defective differentiation resulted in inadequate capillary tube formation, and weak vessels with reduced cellular adhesiveness. Defective haematopoiesis resulted in a reduced erythroid cell number within the yolk sac. Defective yolk sac vasculogenesis and haematopoiesis were present either together, or in isolation of each other. The phenotypes are consistent with the observation of abundant TGF beta 1 gene expression in both endothelial and haematopoietic precursors. The data indicate that the primary effect of loss of TGF beta 1 function in vivo is not increased haematopoietic or endothelial cell proliferation, which might have been expected by deletion of a negative growth regulator, but defective haematopoiesis and endothelial differentiation.

Cis-regulatory elements and transcription factors involved in the regulation of the transforming growth factor-beta 2 gene

Embryonal carcinoma (EC) cells and embryonic stem (ES) cells provide useful model systems for studying differentiation during early mammalian development. Previous studies have demonstrated that differentiation of two restricted mouse EC cell lines is accompanied by activation of the TGF-beta 2 gene. Moreover, one negative and two positive regulatory regions upstream of the transcription start site were identified, which appear to play key roles in the transcriptional regulation of the human TGF-beta 2 gene. In this report, we demonstrate that the same three regulatory regions strongly influence the activity of the TGF-beta 2 promoter in differentiated cells derived from the multipotent human EC cell line, NT2/D1, and from the murine totipotent ES cell line, CCE. We also determined that the same three regions are active in the regulation of the TGF-beta 2 gene in the murine parietal endoderm-like cell line, PYS-2. However, an additional negative regulatory region appears to contribute to the regulation of the TGF-beta 2 gene in PYS-2 cells. Last, mutation of a CRE/ATF element located just upstream of the transcription start site of the TGF-beta 2 gene reduces significantly the activity of the TGF-beta 2 promoter in the differentiated cells. However, in contrast to our previous findings, our gel mobility shift analyses demonstrate that this CRE/ATF element is bound by similar proteins in nuclear extracts prepared from undifferentiated and differentiated mouse EC cells as well as from undifferentiated human EC cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth factors in reproduction

The changes that occur in the female reproductive tract during the menstrual cycle and in early pregnancy, in preparation for embryo implantation and subsequent placental and fetal development, have long attracted the interest of reproductive biologists. The early embryo expresses growth factors and growth factor receptors that are, in general, temporally expressed. In addition, the oviduct and uterine endometrium also synthesize growth factors and cytokines, and the developing embryo finds itself in a growth-factor-rich milieu during early development. The autocrine, juxtracrine, and paracrine actions of these factors in the development of the early embryo and of the maternal reproductive tract are just beginning to be appreciated, as are their potential roles in cellular proliferation and cell-cell communication within the developing embryo, in the reproductive tract, and at the maternal-trophoblast interface. When detailed mechanisms underlying these interactions are fully understood, it is anticipated that therapies will be rationally designed to treat reproductive disorders associated with abnormal embryonic development and poor placentation.

Transforming growth factor-beta 1 in reproduction and development

Expression patterns of TGF-beta s during embryogenesis and in adult reproductive organs, as well as the activities of these molecules in in vitro assays of biological processes relating to reproduction and development, have suggested that TGF-beta s may play a role in both reproductive function and embryonic development. To investigate the function of TGF-beta 1 in vivo, the murine TGF-beta 1 gene was disrupted by gene targeting, and animals that lacked TGF-beta 1 activity were generated. Homozygous mutant animals were obtained which exhibited a multifocal inflammatory disease. However, the observed numbers of homozygous mutant offspring were less than expected, suggesting the occurrence of some type of prenatal lethality. This paper reviews the proposed role of the TGF-beta s in reproductive and developmental processes and discusses observations obtained from the TGF-beta 1 gene-targeting experiments as they relate to these processes.

Epidermal growth factor--induced implantation and decidualization in the rat

Effects of epidermal growth factor (EGF) on blastocyst implantation and experimentally-induced decidualization were examined in the rat. Intraluminal injection of EGF into each uterine horn induced implantation in the ovariectomized progesterone-treated delayed implanting rat in a dose-dependent manner. This induction was inhibited by indomethacin, an inhibitor of prostaglandin synthesis. Intraluminal injection of EGF on day 5 of pseudopregnancy elicited a greater decidual response when compared to the vehicle-injected contralateral uterine horn. These results suggest that EGF may play important roles in the process of implantation and decidualization in the rat.

Heparin-binding EGF-like growth factor gene is induced in the mouse uterus temporally by the blastocyst solely at the site of its apposition: a possible ligand for interaction with blastocyst EGF-receptor in implantation

Heparin-binding EGF-like growth factor (HB-EGF) is a newly discovered member of the EGF family of growth factors. HB-EGF can bind to two loci on cell surfaces, heparan sulphate proteoglycans and EGF-receptor (EGF-R), and either one or both of these interactions could play a role in cell-cell interactions. In the rodent, increased endometrial vascular permeability at the site of blastocyst apposition is considered to be an earliest discernible prerequisite event in the process of implantation and this event coincides with the initial attachment reaction between the blastocyst trophectoderm and uterine luminal epithelium. This investigation demonstrates that the HB-EGF gene is expressed in the mouse uterine luminal epithelium surrounding the blastocyst 6–7 hours before the attachment reaction that occurs at 2200–2300 hours on day 4 of pregnancy. It was further demonstrated that this gene is not expressed in the luminal epithelium at the site of the blastocyst apposition during the progesterone-maintained delayed implantation, but is readily induced in the luminal epithelium surrounding an activated blastocyst after termination of the delay by an estrogen injection. In vitro studies showed that HB-EGF induced blastocyst EGF-R autophosphorylation, and promoted blastocyst growth, zona-hatching and trophoblast outgrowth. These results suggest possible interactions between the uterine HB-EGF and blastocyst EGF-R very early in the process of implantation, earlier than any other embryo-uterine interactions defined to date at the molecular level.

Expression and role of c-myc protooncogene in murine preimplantation embryonic development

PURPOSE

The present study was conducted to investigate the expression and possible role of the c-myc protooncogene in preimplantation embryos by using reverse-transcriptase/polymerase chain reaction (RT-PCR) technique and microinjection of synthetic antisense c-myc oligonucleotide probe, respectively. Total RNA was extracted from oocytes and two cell-, four cell-, early morula-, late morula-, early blastocyst-, and late blastocyst-stage embryos, and cDNA was constructed using MMLV reverse transcriptase. Sense primer (P1) and antisense primer (P2) used were based on the c-myc gene sequence bp 1609-1629 and bp 3279-3299, respectively, that span a 1.37-kb intron. PCR-amplified products of cDNA from oocyte-, two cell-, four cell-, early and late morula-, and blastocyst-stage embryos demonstrated the expected 313-bp product in Southern blot hybridization using a c-myc specific DNA probe, with an indication of lower levels in oocytes and early morulae.

RESULTS

Cytoplasmic injection of the antisense c-myc oligonucleotide probe (P2) and not the sense probe (P1) into pronuclear-stage zygotes caused a significant (P = 0.02 to 0.0001) inhibition of development to blastocysts in a concentration-dependent manner, with a maximal inhibition at the first cleavage of zygotes to two cell-stage embryos. There was no effect on the P2 antisense injection on pronucleus formation.

CONCLUSION

These results indicate that the c-myc protooncogene is expressed in preimplantation embryos and may have an essential role in normal embryogenesis in mice.