Expression of vascular endothelial growth factor (VEGF) and its corresponding receptors (flt-1 and flk-1) in the bovine oviduct

Pluripotency and Growth Factors in Early Embryonic Development of Mammals: A Comparative Approach

The regulation of early events in mammalian embryonic development is a complex process. In the early stages, pluripotency, cellular differentiation, and growth should occur at specific times and these events are regulated by different genes that are expressed at specific times and locations. The genes related to pluripotency and cellular differentiation, and growth factors that determine successful embryonic development are different (or differentially expressed) among mammalian species. Some genes are fundamental for controlling pluripotency in some species but less fundamental in others, for example, Oct4 is particularly relevant in bovine early embryonic development, whereas Oct4 inhibition does not affect ovine early embryonic development. In addition, some mechanisms that regulate cellular differentiation do not seem to be clear or evolutionarily conserved. After cellular differentiation, growth factors are relevant in early development, and their effects also differ among species, for example, insulin-like growth factor improves the blastocyst development rate in some species but does not have the same effect in mice. Some growth factors influence genes related to pluripotency, and therefore, their role in early embryo development is not limited to cell growth but could also involve the earliest stages of development. In this review, we summarize the differences among mammalian species regarding the regulation of pluripotency, cellular differentiation, and growth factors in the early stages of embryonic development.

Microvascularization and Expression of Fibroblast Growth Factor and Vascular Endothelial Growth Factor and Their Receptors in the Mare Oviduct

Simple Summary

The oviduct provides the ideal conditions for fertilization and early embryonic development. Adequate vascularization is essential for proper oviduct physiological function. In this work on the mare oviduct, differences in the oviductal artery and arterioles and their ramifications in the infundibulum, ampulla and isthmus were examined. Locally, vascularization is modulated by the action of angiogenic factors, mediated by their specific receptors. In the present study, the isthmus presented the largest vascular area and the highest number of vascular structures in the follicular phase. We have also shown that the relative abundance of angiogenic transcripts and proteins, such as fibroblast growth factor 1 (FGF1) and 2 (FGF2) and vascular endothelial growth factor (VEGF), and their respective receptors (FGFR1, FGFR2, VEGFR2 = KDR), were present in all portions of the oviduct throughout the estrous cycle. There was an increase in the transcripts of angiogenic receptors FGF1 and FGFR1 in the ampulla and isthmus, and of FGF2 and KDR in the isthmus. This was also observed in the isthmus, where the relative abundance of proteins FGFR1 and KDR was the highest. This study shows that the equine oviduct presents differences in microvascular density in its portions. The angiogenic factors VEGF, FGF1, FGF2 and their respective receptors are expressed in all studied regions of the mare oviduct, in agreement with microvascular patterns.

Abstract

The oviduct presents the ideal conditions for fertilization and early embryonic development. In this study, (i) vascularization pattern; (ii) microvascular density; (iii) transcripts of angiogenic factors (FGF1, FGF2, VEGF) and their receptors—FGFR1, FGFR2, KDR, respectively, and (iv) the relative protein abundance of those receptors were assessed in cyclic mares’ oviducts. The oviductal artery, arterioles and their ramifications, viewed by means of vascular injection-corrosion, differed in the infundibulum, ampulla and isthmus. The isthmus, immunostained with CD31, presented the largest vascular area and the highest number of vascular structures in the follicular phase. Transcripts (qPCR) and relative protein abundance (Western blot) of angiogenic factors fibroblast growth factor 1 (FGF1) and 2 (FGF2) and vascular endothelial growth factor (VEGF), and their respective receptors (FGFR1, FGFR2, VEGFR2 = KDR), were present in all oviduct portions throughout the estrous cycle. Upregulation of the transcripts of angiogenic receptors FGF1 and FGFR1 in the ampulla and isthmus and of FGF2 and KDR in the isthmus were noted. Furthermore, in the isthmus, the relative protein abundance of FGFR1 and KDR was the highest. This study shows that the equine oviduct presents differences in microvascular density in its three portions. The angiogenic factors VEGF, FGF1, FGF2 and their respective receptors are expressed in all studied regions of the mare oviduct, in agreement with microvascular patterns.

The urokinase plasminogen activator system components are regulated by vascular endothelial growth factor D in bovine oviduct

SummaryThe mammalian oviduct plays a pivotal role in the success of early reproductive events. The urokinase plasminogen activator system (uPAS) is present in the bovine oviduct and is involved in extracellular matrix remodelling through plasmin generation. This system can be regulated by several members of the vascular endothelial growth factors (VEGF) and their receptors. In this study, the VEGF-D effect on the regulation of uPAS was evaluated. First, RT-polymerase chain reaction (PCR) analyses were used to evidence the expression of VEGF-D and its receptors in oviductal epithelial cells (BOEC). VEGF-D, VEGFR2 and VEGFR3 transcripts were found in ex vivo and in vitro BOEC, while only VEGFR2 mRNA was present after in vitro conditions. VEGF-D showed a regulatory effect on uPAS gene expression in a dose-dependent manner, inducing an increase in the expression of both uPA and its receptor (uPAR) at 24 h post-induction and decreases in the expression of its inhibitor (PAI-1). In addition, the regulation of cell migration induced by VEGF-D and uPA in BOEC monolayer cultures was analyzed. The wound areas of monolayer cultures incubated with VEGF-D 10 ng/ml or uPA 10 nM were modified and significant differences were found at 24 h for both stimulations. These results indicated that uPAS and VEGF-D systems can modify the arrangement of the bovine oviductal epithelium and contribute to the correct maintenance of the oviductal microenvironment.

Immunolocalization of angiogenic growth factors in the ovine uterus during the oestrus cycle and in response to Steroids

The vascular changes associated with endometrial maturation in preparation for embryo implantation depend on numerous growth factors, known to regulate key angiogenic events. Primarily, the vascular endothelial growth factor (VEGF) family promotes vascular growth, whilst the angiopoietins maintain blood vessel integrity. The aim was to analyse protein levels of VEGFA ligand and receptors, Angiopoietin-1 and 2 (ANG1/2) and endothelial cell receptor tyrosine kinase (TIE-2) in the ovine endometrium in the follicular and luteal phases of the oestrus cycle and in response to ovarian steroids. VEGFA and its receptors were localized in both vascular cells and non-vascular epithelium (glandular and luminal epithelium) and stroma cells. VEGFA and VEGFR2 proteins were elevated in vascular cells in follicular phase endometrium, compared to luteal phase, most significantly in response to oestradiol. VEGFR1 was expressed by epithelial cells and endothelial cells and was stimulated in response to oestradiol. In contrast, Ang-1 and Ang-2 proteins were elevated in luteal phase endometrium compared to follicular phase, and in response to progesterone, evident in vascular smooth muscle cells and glands which surround TIE-2-expressing blood vessels. Our findings indicate that VEGFA is stimulated by oestradiol, most predominantly in follicular phase endometrium, and Ang-1 and 2 are stimulated by progesterone and were increased during the luteal phase of the oestrus cycle, during the time of vascular maturation.

Spatial differences in gene expression in the bovine oviduct

The aim of this study was to compare the transcriptome of the oviductal isthmus of pregnant heifers with that of cyclic heifers as well as to investigate spatial differences between the transcriptome of the isthmus and ampulla of the oviduct in pregnant heifers. After synchronizing crossbred beef heifers, those in standing oestrus (=Day 0) were randomly assigned to cyclic (non-bred, n=6) or pregnant (artificially inseminated, n=11) groups. They were slaughtered on Day 3 and both oviducts from each animal were isolated and cut in half to separate ampulla and isthmus. Each portion was flushed to confirm the presence of an oocyte/embryo and was then opened longitudinally and scraped to obtain epithelial cells which were snap-frozen. Oocytes and embryos were located in the isthmus of the oviduct ipsilateral to the corpus luteum Microarray analysis of oviductal cells revealed that proximity to the corpus luteum did not affect the transcriptome of the isthmus, irrespective of pregnancy status. However, 2287 genes were differentially expressed (P<0.01) between the ampulla and isthmus of the oviduct ipsilateral to the corpus luteum in pregnant animals. Gene ontology revealed that the main biological processes overrepresented in the isthmus were synthesis of nitrogen, lipids, nucleotides, steroids and cholesterol as well as vesicle-mediated transport, cell cycle, apoptosis, endocytosis and exocytosis, whereas cell motion, motility and migration, DNA repair, calcium ion homeostasis, carbohydrate biosynthesis, and regulation of cilium movement and beat frequency were overrepresented in the ampulla. In conclusion, large differences in gene expression were observed between the isthmus and ampulla of pregnant animals at Day 3 after oestrus.

Influence of vascular endothelial growth factor and Cysteamine on in vitro bovine oocyte maturation and subsequent embryo development

The objective of this study was to investigate the effect of VEGF and Cysteamine during in vitro maturation (IVM) of bovine oocytes on GSH content and developmental competence. For this purpose, experiments were designed to evaluate the effect of 0, 100, 300, and 500 ng/mL VEGF in IVM medium on: GSH content in oocytes and cumulus cells (Exp. 1) and subsequent embryo development (Exp. 2). Also, influence of adding 500 ng/mL VEGF and 100 μM Cysteamine to IVM medium on GSH content in oocytes and cumulus cells (Exp. 3) and oocyte developmental capacity (Exp. 4) were evaluated. Oocytes were matured in: a) Control; b) VEGF 0-3 h; c) Cysteamine 4-24 h; d) VEGF 0-3 h + Cysteamine 4-24 h; and e) VEGF + Cysteamine 24 h. The results showed that: i) VEGF did not alter GSH content in oocytes and cumulus cells; (ii) supplementation of 300 and 500 ng/mL VEGF increased blastocyst yield; (iii) the presence of VEGF + Cysteamine simultaneously during 24 h improved GSH content but not embryo development; and (iv) the presence of VEGF during the first 3 h + Cysteamine from 4 to 24 h increased GSH concentrations and subsequent embryo development. In conclusion, the addition of VEGF and Cysteamine in two sequential steps to maturation medium result in an improvement of cytoplasmic maturation, with a positive impact on oocyte developmental capacity by increasing the efficiency of in vitro blastocyst production. However, the effect was detrimental when both VEGF and Cysteamine were present during 24 of IVM.

Steroids in the equine oviduct: synthesis, local concentrations and receptor expression

Steroids play an important role in mammalian reproduction and early pregnancy. Although systemic changes in steroid concentrations have been well documented, it is not clear how these correlate with local steroid concentrations in the genital tract. We hypothesised that, in the horse, the preimplantation embryo may be subjected to high local steroid concentrations for several days. Therefore, we measured progesterone, 17-hydroxyprogesterone, 17?-oestradiol, testosterone and 17?-testosterone concentrations in equine oviductal tissue by ultra-HPLC coupled with tandem mass spectrometry, and progesterone, 17?-oestradiol, oestrone and testosterone concentrations in oviduct fluid by radioimmunoassay, with reference to cycle stage and side of ovulation. Progesterone concentrations were high in oviductal tissue and fluid ipsilateral to the ovulation side during dioestrus, whereas other steroid hormone concentrations were not influenced by the side of ovulation. These results suggest that the high ipsilateral progesterone concentration is caused by: (1) contributions from the follicular fluid in the oviduct and diffusion of follicular fluid steroids after ovulation; (2) local transfer of steroids via blood or lymph; (3) local synthesis of progesterone in the oviduct, as evidenced by the expression of steroidogenic enzymes; and (4) a paracrine contribution from follicular cells. These data provide a basis for the study of the importance of endocrine and paracrine signalling during early embryonic development in the horse.

Expression of the vascular endothelial growth factor receptor system in porcine oviducts after induction of ovulation and superovulation

This study was performed to determine the influence of insemination as well as treatment with human chorionic gonadotropin (hCG) and equine chorionic gonadotropin (eCG) on expression of the vascular endothelial growth factor (VEGF) system in porcine oviducts. In the first experiment, 10 gilts were assigned to 2 groups: cyclic (treated with phosphate-buffered saline; n = 5) and inseminated (n = 5). In experiment II, 15 gilts were assigned to 3 groups: inseminated (control; n = 5), induced ovulation and inseminated (750 IU eCG, 500 IU hCG; n = 5), and superovulated and inseminated (1500 IU eCG, 1000 IU hCG; n = 5). Oviducts (isthmus and ampulla) were collected 3 days after phosphate-buffered saline treatment (experiment I) or insemination. Blood samples were collected during slaughter for E2 (estradiol) and P4 (progesterone) analysis. Levels of messenger RNA (mRNA) of the VEGF system were analyzed by real-time polymerase chain reaction and protein by Western blot and E2 and P4 using radioimmunoassays. Insemination by itself decreased VEGF120 mRNA expression and VEGF-A protein level in the oviductal isthmus (P < 0.05) but did not alter VEGF164 mRNA. Expression of Flt-1 (c-fms-like tyrosine kinase VEGFR-1) mRNA increased in the isthmus of inseminated relative to cyclic gilts (P < 0.05), whereas KDR (fetal liver kinase-1 VEGFR-2) mRNA levels decreased in both the oviductal isthmus (P < 0.05) and ampulla (P < 0.001). Superovulation decreased VEGF120 and VEGF164 mRNA expression in the isthmus compared with the inseminated group (P < 0.05), and lowered protein levels of VEGF-A in the isthmus of both stimulated groups (P < 0.001). Expression of Flt-1 mRNA was affected by hCG and eCG treatment in both gonadotropin-stimulated groups in the isthmus as well as in the ampulla (P < 0.001) and protein levels in the ampulla of superovulated gilts (P < 0.05). Protein levels of KDR were reduced in the oviductal ampulla of gilts in both the induced ovulation and superovulated groups (P < 0.05). The concentrations of both E2 and P4 increased significantly in superovulated group of gilts (P < 0.01 and P < 0.05 for E2 and P4, respectively). Our study showed that insemination alone as well as ovarian stimulation affected the mRNA and protein profiles of the VEGF system in the porcine oviduct. Disrupted VEGF system expression may be crucial to many events occurring during the periovulatory period and consequently could lead to deprivation of VEGF-dependent factors that are necessary for proper fertilization, gamete transport, and embryo development.

Equine oviduct explant culture: a basic model to decipher embryo–maternal communication

Equine embryos remain for 6 days in the oviduct and thus there is a need for an in vitro model to study embryo–oviductal interactions in the horse, since this subtle way of communication is very difficult to analyse in vivo. Until now, no equine oviduct explant culture model has been characterised both morphologically and functionally. Therefore, we established a culture system for equine oviduct explants that maintained epithelial morphology during 6 days of culture, as revealed by light microscopy and transmission electron microscopy. We demonstrated the presence of highly differentiated, tall columnar, pseudostratified epithelium with basal nuclei, numerous nucleoli, secretory granules and apical cilia, which is very similar to the in vivo situation. Both epithelium and stromal cells originating from the lamina propria are represented in the explants. Moreover, at least 98% of the cells remained membrane intact and fewer than 2% of the cells were apoptotic after 6 days of culture. Although dark-cell degeneration, which is a hypoxia-related type of cell death, was observed in the centre of the explants, quantitative real-time PCR failed to detect upregulation of the hypoxia-related marker genes HIF1A, VEGFA, uPA, GLUT1 and PAI1. Since the explants remained morphologically and functionally intact and since the system is easy to set up, it appears to be an excellent tool for proteome, transcriptome and miRNome analysis in order to unravel embryo–maternal interactions in the horse.

Does seminal plasma affect angiogenesis in the porcine oviduct?

In the present study we examined the effect of seminal plasma (SP) on angiogenesis in the porcine oviduct. Gene expressions of vascular endothelial growth factor (VEGF) and its two receptors (Flt-1: fms-like tyrosine kinase and Flk-1/KDR: fetal liver kinase-1/kinase insert domain-containing receptor) as well as fibroblast growth factors (FGF-1 and 2) and von Willenbrand factor (VWF) were determined in the oviduct of SP-treated and control (PBS-treated) gilts. Moreover, vascular density (VD) indicated by endothelial cell area immunolocalized by VWF staining, was assessed in the oviducts. Real-time PCR revealed significantly higher expression of FGF-2 and VWF on day 1 (p<0.05) after SP administration in comparison to control animals. In contrast, Flt-1 mRNA level on day 1 was lower in SP-treated gilts compared to controls (p<0.05). In the examined oviductal sections, VD did not differ between control and SP-treated animals. However, in SP-treated animals VD was higher on day 5 than on day 1 (p<0.05) or 3 (p<0.01). SP had no significant effect on VEGF, Flk-1/KDR and FGF-1 mRNA expression. In conclusion, our results suggest that SP affects the vascular network by changing the expression of factors contributing to angiogenesis.

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

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

Dexamethasone-induced eosinopenia is associated with lower progesterone production in cattle

Eosinophilic cells accumulate in the capillaries of the bovine Graafian follicle shortly before ovulation and in the early developing corpus luteum (CL). Suppressing the migration of these eosinophilic cells by dexamethasone allowed us to evaluate their possible function in the CL development. Brown Swiss cows (n = 10) were randomly subdivided into two groups (n = 5). Every group was used once as control group and once as experimental group with two oestrous cycles between each treatment. Eighteen hours (h) after oestrus synchronization, dexamethasone or saline was given. Ovulation was induced 24 h later with gonadotropin-releasing hormone. Another injection of dexamethasone or saline was given 12 h later. Eosinophilic cells in the blood were counted daily until day 7 after the first dexamethasone injection. The collection of ovaries took place at days 1, 2 and 5. Gene expression, protein concentration and location of angiogenic factors, chemokines, insulin-like growth factor 1 (IGF1) and eosinophilic cells were studied. No eosinophilic cells were found in the CL of the treatment group. Blood progesterone decreased significantly in the dexamethasone group from day 8 to 17. The protein concentration of FGF2 increased significantly in CL tissue at day 2 and VEGFA decreased. Local IGF1 gene expression in the CL was not regulated. We assume from our data that the migration of eosinophilic cells into the early CL is not an essential, but an important stimulus for angiogenesis during early CL development in cattle.

Mechanisms for the establishment of pregnancy in the pig

Establishment of pregnancy in pigs requires continuous function of corpora lutea and endometrial preparation for embryo implantation. Progesterone regulates expression of many proteins necessary for endometrial remodelling and embryo-maternal communications. Attaining the uterine receptivity involves progesterone priming and loss of progesterone receptors in the uterine epithelium before days 10-12 after oestrus. Spermatozoa and oocytes in oviduct alter secretion of specific proteins that exert beneficial effect on gametes and embryos. Moreover, an appropriate leucocyte activation and maintenance of delicate cytokine balance within the oviduct and uterus are important for early pregnancy. This early local immune response is rather mediated by seminal plasma components. These components also influence prostaglandin (PG) synthesis in the oviduct that is important for gamete and embryo transport. Pregnancy establishment requires the biphasic pattern of oestrogen secretion by conceptuses on days 11-12 and 15-30. Conceptus affects lipid signalling system consisting of prostaglandins and lysophosphatic acid. PG synthesis is changed by conceptus signals in favour of luteoprotective PGE(2) . Additionally, existence of PGE(2) positive feedback loop in the endometrium contributes to increased PGE(2) /PGF(2α) ratio during the peri-implantation period. PGE(2) through endometrial PGE(2) receptor (PTGER2) elevates the expression of enzymes involved in PGE(2) synthesis. Higher PGE(2) secretion in uterine lumen coincides with the elevated expression of HOXA10 transcription factor critical for implantation. A stable adhesion between conceptus and endometrium requires reduction in mucin-1 on the apical surface of epithelium and integrin activation by extracellular matrix proteins. Furthermore, growth factors, cytokines and its receptors are involved in embryo-maternal interactions.

Immunohistochemical assessment of intrinsic and extrinsic markers of hypoxia in reproductive tissue: differential expression of HIF1α and HIF2α in rat oviduct and endometrium

Hypoxia is thought to be critical in regulating physiological processes within the female reproductive system, including ovulation, composition of the fluid in the oviductal/uterine lumens and ovarian follicle development. This study examined the localisation of exogenous (pimonidazole) and endogenous [hypoxia inducible factor 1α and 2α (HIF1α, -2α), glucose transporter type 1 (GLUT1) and carbonic anhydrase 9 (CAIX)] hypoxia-related antigens within the oviduct and uterus of the rat reproductive tract. The extent to which each endogenous antigen co-compartmentalised with pimonidazole was also assessed. Female Wistar Furth rats (n = 10) were injected intraperitoneally with pimonidazole (60 mg/kg) 1 h prior to death. Reproductive tissues were removed immediately following death and fixed in 4% paraformaldehyde before being embedded in paraffin. Serial sections were cut (6-7 μm thick) and antigens of interest identified using standard immunohistochemical procedures. The mucosal epithelia of the ampulla, isthmus and uterus were immunopositive for pimonidazole in most sections. Co-compartmentalisation of pimonidazole with HIF1α was only expressed in the mucosa of the uterus whilst co-compartmentalisation with HIF2α was observed in the mucosa of the ampulla, isthmus and uterus. Both GLUT1 and CAIX were co-compartmentalised with pimonidazole in mucosa of the isthmus and uterus. This study confirms that mucosal regions of the rat oviduct and uterus frequently experience severe hypoxia and there are compartment specific variations in expression of endogenous hypoxia-related antigens, including the HIF isoforms. The latter observation may relate to target gene specificity of HIF isoforms or perhaps HIF2α's responsiveness to non-hypoxic stimuli such as hypoglycaemia independently of HIF1α.

The expression of vascular endothelial growth factor and its receptors (flt1/fms, flk1/KDR, flt4) and vascular endothelial growth inhibitor in the bovine uterus during the sexual cycle and their correlation with serum sex steroids

The present study was conducted to demonstrate of the immunohistochemical localization of vascular endothelial growth factor (VEGF) and its receptors (flt1/fms, flk1/KDR and flt4) as well as vascular endothelial growth inhibitor (VEGI) and to determine the correlation of VEGF and its receptors and VEGI with serum sex steroids (estrogen and progesterone) in the bovine uterus during the sexual cycle. The stage of the estrous cycle in 30 Holstein cattle was assessed based on the gross and histological appearance of the ovaries and uterus and on blood steroid hormone levels. Tissue samples obtained from the uterus were fixed in 10% formaldehyde for routine histological processing. During both follicular and luteal phases, positive cytoplasmic and membrane staining was achieved for VEGF and its receptors (flt1/fms, flk1/KDR and flt4) as well as VEGI in the luminal and glandular epithelial cells, the connective tissue and smooth muscle cells, and the vascular endothelial cells and smooth muscle cells in the uterus. The intensity, proportional and total scores determined for VEGF and its receptors (flt1/fms and flt4) as well as VEGI were greater in the luminal and glandular epithelial cells compared to the connective tissue and smooth muscle cells (P < 0.05). Furthermore, the number and intensity of the flk1/KDR positive cells were greater among the connective tissue cells compared to the luminal and glandular epithelial cells (P < 0.05). As a result, it was determined that the expression of VEGF and its receptors as well as VEGI in the bovine uterus during the follicular and luteal phases varied with different cell types. This suggests that depending on the stage of the sexual cycle, these factors may mediate the establishment of an appropriate environment for the nutritional supply and implantation of the embryo primarily due to the stimulation of angiogenesis but also through the increase in the secretory activity of the epithelial cells in the uterus. Furthermore, this indicates that ovarian steroid hormones play a significant role in regulating the expression of VEGF and its receptors as well as VEGI.

Gamete/embryo – oviduct interactions: implications onin vitroculture

Fertilization and development of mouse embryos occur in the oviduct. Accumulating data suggested that embryo-maternal communication exists in the preimplantation period, with the female reproductive tract providing the optimal microenvironment conducive to the development of embryos. Signals produced from the developing embryos not only affect their own transport in the oviduct, but the physiology and gene expression patterns of the oviduct. As a step towards understanding the action of embryos on oviductal physiology, both genomics and proteomics approaches are being used to unveil the underlying mechanism of embryo-maternal interaction at the preimplantation stage. Results from recent studies allow us to better understand the roles and the use of oviductal secretory proteins or factors that affect embryo development in vivo and in vitro. It has been shown that in vitro culture alters gene expression of the cultured embryos and may predispose the embryo to certain disease. Therefore, the interaction between gamete/embryo and oviduct in vitro and in vivo, and the long-term effects of embryo culture on foetal development warrant further investigation.

Vascular endothelial growth factor stimulates the primary to secondary follicle transition in bovine follicles in vitro

Little is known about the mechanisms regulating the growth of early preantral follicles, especially in nonrodent mammalian species. To test the hypothesis that vascular endothelial growth factor (VEGF) promotes the primary to secondary follicle transition, pieces of bovine fetal ovarian cortex were cultured with VEGF (0, 1, 10, or 100 ng/ml) for 0 or 10 days, followed by morphometric analysis. On day 0, cortical pieces contained mostly primordial follicles, but after 10 days in vitro most primordial follicles had activated, differentiating into primary follicles. VEGF had no effect on the numbers of primordial or primary follicles, compared with untreated controls, but all doses increased the number of secondary follicles. In the second experiment, a range of lower doses of VEGF (0.1-10 ng/ml) increased the number of secondary follicles in a dose-dependent manner. Analysis of VEGF transcripts by RT-PCR showed expression of mRNA for three isoforms of VEGF (VEGF121, 165, and 189) in fetal bovine ovarian cortex, with VEGF121 and 165 expressed predominantly and levels of mRNA for VEGF121 and 189 increasing after day 211 of gestation, when the first secondary follicles appear. Expression of mRNA for both VEGF receptors (flt-1 and flk-1) was also detected, but did not change with the development of fetal ovaries. Immunohistochemistry revealed positive staining for VEGF in blood vessels and in follicle cells of secondary follicles, consistent with Western blot analyses showing increases in VEGF protein as ovarian development progressed. Taken together, the results provide support for a role for VEGF in the primary to secondary follicle transition.

Vascular endothelial growth factor plays more than an angiogenic role in the female reproductive system

Although the most well-known function of vascular endothelial growth factor is its angiogenic activity, it plays more than a simple angiogenic role in the female reproductive system as it is involved in a number of key events in the course of the ovulatory cycle. The modulation of vascular endothelial growth factor expression varies in different reproductive tissues, probably related to its various functions at these different sites.

Demilune cell and parotid protein from murine oviductal epithelium stimulates preimplantation embryo development

In mammals, fertilization and early preimplantation embryo development occur in the oviduct. We hypothesized that interaction exists between the developing embryos and the maternal genital tract, such that the embryos modulate the physiology and gene expression of the oviduct so that it is conducive to their development. By comparing the gene expression patterns in mouse oviducts containing transferred preimplantation embryos with those of oviducts containing oocytes, we report here the characterization of demilune cell and parotid protein (Dcpp), which was up-regulated in the embryo-containing oviduct. Dcpp mRNA was highly expressed in the oviductal epithelium at the estrus stage. The Dcpp gene codes for a protein of 150 amino acids and contains a signal peptide suggestive of secretory function. The Dcpp mRNA level was maintained in the oviductal epithelium of pregnant females but decreased continuously in those of pseudopregnant mice. Exogenous estrogen stimulated the expression of Dcpp mRNA and protein in ovariectomized mice. The effect was abolished by an estrogen antagonist, ICI 182,780. Dcpp protein was present in mouse oviductal fluid but not in uterine fluid. More importantly, Dcpp immunoreactivity was found in embryos recovered from the oviduct but not in mature oocytes from the ovary. Supplementation of Dcpp to culture medium stimulated the development of mouse embryos to the blastocyst stage. Anti-Dcpp antibody decreased the beneficial effect of Dcpp on implantation of two-cell mouse embryos transferred to the oviducts of the foster mothers. In summary, our data demonstrated that Dcpp is highly expressed in the oviductal lumen in the presence of preimplantation embryos. It stimulates the growth of preimplantation embryos and may play an important role in embryo-maternal dialogue.

Vascular endothelial growth factor system in the cow oviduct: A possible involvement in the regulation of oviductal motility and embryo transport

Vascular endothelial growth factor (VEGF) is a potent angiogenic and permeability enhancing factor, which shows the highest activity in the oviduct during the periovulatory period of the estrous cycle in cattle. It has also been shown that the contraction activity of oviduct is highest during the periovulatory period. The present study therefore focused on the possible involvement of VEGF in the regulation of biosynthesis and secretion of contraction-relaxation-related substances in the cow oviduct. Possible autonomous VEGF system in the oviduct as well as its endocrine control was also studied. Bovine oviductal epithelial cells (BOEC) in the second passage were cultured with VEGF (1 ng/ml) alone or with luteinizing hormone (LH; 10 ng/ml), estradiol 17-beta (E2; 1 ng/ml), and/or progesterone (P4; 1 ng/ml). The levels of prostaglandins (PGs), endothelin-1 (ET-1), and angiotensin II (Ang II) in the medium were measured using second antibody enzymeimmunoassay (EIA). The mRNA expressions for cycloxygenase-2 (Cox-2), prostaglandin F synthase (PGFS), prostaglandin E synthase (PGES), prepro-ET-1, endothelin converting enzyme-1 (Ece-1), angiotensin converting enzyme-1 (Ace-1), VEGF and its receptors were investigated using real-time RT-PCR. The results indicate that, (1) VEGF dose-dependently stimulated the release of prostaglandin E2 (PGE2), prostaglandin F2alpha (PGF2alpha), and ET-1, but not Ang II. VEGF and VEGF with LH, E2, and P4 upregulated mRNA expression for biosynthesis cascade of PG, ET-1 as well as their release. However, only the combination of VEGF with LH, E2, and P4 upregulated mRNA for Ace-1 and Ang II release, but not VEGF alone. (2) Treatments of LH, with E2 and/or P4 increased the mRNA expression for VEGF, Flk-1 and Flt-1, and (3) VEGF itself downregulated the expression of mRNA for VEGF, and LH, E2, and P4 enhanced this downregulatory effect. The results of the present study provide the first evidence that (1) VEGF directly stimulates the biosynthesis and release of PGE2, PGF2alpha, and ET-1 in the bovine oviduct, (2) LH stimulates the oviductal VEGF system, and (3) VEGF downregulates the oviductal VEGF system and this downregulation was further intensified in the presence of LH. The data suggest that the preovulatory LH-surge, together with increasing E2 secretion from the Graffian follicle and basal P4 levels from the regressing corpus luteum (CL), upregulates the oviductal VEGF system, inducing the maximum oviductal production of contraction-relaxation-related substances for active oviduct contraction and rapid transport of gametes to the fertilization site. However, the oviductal VEGF elevation caused by the LH-surge, appears to downregulate the oviductal VEGF system immediately after ovulation thereby may contribute to suppress oviductal contraction to secure slow transport of the embryo to the uterus at the optimal time.

The effect of exogenous estradiol treatment on the mRNA expression of vascular endothelial growth factor and its receptors in cultured human oviduct mucosal cells

PURPOSE

To evaluate the responses of cultured oviduct mucosal cells to exogenous estradiol treatment in regulating the mRNA expression of vascular endothelial growth factor (VEGF) and its receptors.

METHODS

The mucosal layer of the ampullary regions of the human oviduct was isolated and cultured with (study groups) or without (control group) the addition of exogenous estradiol in five different concentrations. Semiquantitative reverse-transcriptase-polymerase chain reaction was performed on the oviduct mucosal cells before and after the 6-day culture.

RESULTS

There were no significant differences in the mRNA expression of VEGF and its receptors, both KDR and flt-1, between the five study groups and the control group.

CONCLUSIONS

The mRNA expression of VEGF and its receptors is not altered by exogenous estradiol treatment in cultured oviduct. This helps to explain the mechanism of temporal regulation of VEGF in human oviduct, which reaches the peak level in the peri-ovulatory stage when both the serum estradiol and gonadotropins concentrations are high.

New blood vessel formation and expression of VEGF receptors after implantation of platelet growth factor-enriched biodegradable nanocrystalline hydroxyapatite

Vascular endothelial growth factor (VEGF) plays a key role for the interaction of osteoblasts and endothelial cells and, therefore, is an important factor for the osteointegration of bone substitutes. The aim of the current work was to study the effects of platelet growth factors (PLF) on new blood vessel formation and VEGF-receptors expression pattern in bone defects filled with nanocrystalline hydroxyapatite (HA) paste in miniature-pigs. Conventional histology, RT-PCR for VEGF and receptors mRNA, Western blot analysis, immunohistochemical staining and quantitative assessment of newly formed vessels was performed. HA enriched with platelet growth factor (HA/PLF+) led to an up-regulation of VEGF-R1 synthesis, a slightly enhanced number of newly formed vessels with higher sprouting activity compared with HA without PLF (HA/PLF-) filling defects. These observation are most likely attributable to a stimulating effect of TGF-ss from the platelet factor on VEGF expression in osteoblasts.

Expression pattern of fibroblast growth factor (FGF) and vascular endothelial growth factor (VEGF) system members in bovine corpus luteum endothelial cells during treatment with FGF-2, VEGF or oestradiol

The development of the corpus luteum (CL) is accompanied by very active angiogenesis. We hypothesize that during this process endothelial cells (EC) are under the control of several angiogenic factors and steroids. The aim of this study was to examine the expression of the angiogenic growth factor systems - fibroblast growth factor (FGF) and vascular endothelial growth factor (VEGF) - in EC derived from the bovine CL. Endothelial cells were cultured in serum-free medium and treated for 24 h with different concentrations of oestradiol (range from 10(-13) to 10(-5) mol/l), VEGF or FGF-2 (1, 10 and 100 ng/ml, respectively) and compared with untreated controls. Cells were harvested, total RNA extracted and subjected to semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Treatment with oestradiol or FGF-2 stimulated the expression of FGF-2, but VEGF treatment showed no effect on the FGF-2 expression. FGF-2 or VEGF treatment resulted in an up-regulation of the FGF receptor (FGFR) mRNA. However, no FGF-1 expression was detected in EC. For the VEGF system, treatment with FGF-2, VEGF or oestradiol did not affect VEGF expression. However, the presence of FGF-2 in the medium up-regulated the expression of both VEGF receptors (VEGFR-1 and VEGFR-2), whereas oestradiol or VEGF treatment showed no effect on the expression of these receptors. Our results reveal that functional angiogenic growth factor systems were expressed in vitro in bovine EC derived from the CL. This suggests that the angiogenic FGF and VEGF system members were regulated by FGF or VEGF, but not by oestradiol-17beta.

N-acetylglucosaminyltransferase I activity of bovine oviduct epithelial cells: stimulation by luteinizing hormone, vascular endothelial growth factor and tumor necrosis factor alpha

N-acetylglucosaminyltransferase I (GnT I; EC 2.4.1.101), which catalyzes the first step in the conversion of oligomannose to complex or hybrid N-glycans of glycoproteins, was found in media cultured with bovine oviduct epithelial cells (BOEC) obtained from non-pregnant cows during the follicular phase. Combined treatment with specific hormones increased GnT I release from BOEC. Luteinizing hormone (LH; 10 ng/ml) alone slightly, but together with 17beta-estradiol (E2; 1 ng/ml), synergistically increased GnT I activity. Vascular endothelial growth factor (VEGF) and tumor necrosis factor (TNF) alpha, which have been shown to have their highest activities in the bovine oviduct during the periovulatory period, also increased in GnT I activity. This study provides the first evidence of an increase of GnT I release from BOEC in vitro, and shows that endocrine as well as local factors such as LH, VEGF and TNFalpha increase this activity. The results suggest that GnT I activity in the bovine oviduct may contribute to the induction of glycosylation and thereby contributing to the provision of the optimal microenvironment for fertilization and early development of the embryos.

Regulation of the immunoexpression of aquaporin 9 by ovarian hormones in the rat oviductal epithelium

The volume of oviductal fluid fluctuates during the estrous cycle, suggesting that water availability is under hormonal control. It has been postulated that sex-steroid hormones may regulate aquaporin (AQP) channels involved in water movement across cell membranes. Using a functional assay (oocytes of Xenopus laevis), we demonstrated that the rat oviductal epithelium contains mRNAs coding for water channels, and we identified by RT-PCR the mRNAs for AQP5, -8, and -9, but not for AQP2 and -3. The immunoreactivity for AQP5, -8, and -9 was localized only in epithelial cells of the oviduct. The distribution of AQP5 and -8 was mainly cytoplasmic, whereas we confirmed, by confocal microscopy, that AQP9 localized to the apical plasma membrane. Staining of AQP5, -8, and -9 was lost after ovariectomy, and only AQP9 immunoreactivity was restored after estradiol and/or progesterone treatments. The recovery of AQP9 reactivity after ovariectomy correlated with increased mRNA and protein levels after treatment with estradiol alone or progesterone administration after estradiol priming. Interestingly, progesterone administration after progesterone priming also induced AQP9 expression but without a change in mRNA levels. Levels of AQP9 varied along the estrous cycle with their highest levels during proestrus and estrus. These results indicate that steroid hormones regulate AQP9 expression at the mRNA and protein level and that other ovarian signals are involved in the expression of AQP5 and -8. Thus hormonal regulation of the type and quantity of water channels in this epithelium might control water transport in the oviductal lumen.

Phospholipid transfer protein (PLTP) mRNA expression is stimulated by developing embryos in the oviduct

In mammal, fertilization and early preimplantation embryo development occurs in the oviduct. Evidence is accumulating that the oviductal epithelia secrete various biomolecules to the lumen during the secretory phase of the estrus cycle to enhance embryo development. This secretory activity of the oviduct is under the regulation of steroid hormones. Observations also suggested that the gametes and embryos modulate the physiology and gene-expressing pattern of the oviduct. However, the underlying molecular changes remain elusive. We hypothesize that the developing embryos interact with the surrounding environment and affect the gene expression patterns of the oviduct, thereby modulating the oviductal secretory activity conducive to the preimplantation embryo development. To test this hypothesis, suppression subtractive hybridization (SSH) was used to compare the gene expressions in mouse oviduct containing transferred in vitro cultured preimplantation embryos with that of oviduct containing oocytes during the preimplantation period. We reported here the identification and characterization of phospholipids transfer protein (PLTP), which is highly expressed in the embryo-containing oviduct and localized at the oviductal epithelium by in situ hybridization. PLTP contains signal peptide putative for secretory function. More importantly, PLTP mRNA increases in the oviductal epithelia of pregnant, but not pseudo-pregnant mice when assayed by real-time PCR. Taken together, our data suggested that PLTP may play important role(s) during in vivo preimplantation embryo development. This molecule would be a target to delineate the mechanisms and the roles of oviductal secretory proteins on early embryonic development.

Upregulation of mRNA expression of vascular endothelial growth factor and its receptors by exogenous human chorionic gonadotropin in cultured oviduct mucosal cells

The mucosal cells were isolated from the ampullary regions of 20 human oviducts and cultured with or without hCG in five different concentrations (1-100 ng/mL). As analyzed by the semiquantitative reverse-transcriptase polymerase chain reaction, hCG treatment significantly increased mRNA expression of vascular endothelial growth factor and its receptor flt-1 in the cultured mucosal cells in a dose-dependent manner but had no effect on the expression of another receptor, KDR.

Vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) expression during induced luteolysis in the bovine corpus luteum

Angiogenic factors, like vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF), and their receptors, are strongly regulated during the development of bovine corpus luteum (CL). The aim of this study was to investigate real-time changes of these factors in luteal tissue of cows (n = 4-5 per group) in the mid-luteal phase (day 8-12) after intramuscular injection of the PGF2alpha-analog Cloprostenol. Before (control) and 2, 4, 12, 48, and 64 hr after prostaglandin (PG) injection, CL were collected by transvaginal ovariectomy. RT-PCR for VEGF, VEGF-receptor type 1 (VEGF-R1), VEGF-R2, acidic FGF (FGF-1), basic FGF (FGF-2), and FGF-receptor (FGF-R) was performed. Additionally, the protein concentration for VEGF was determined. The mRNA expression of VEGF and its two receptors (VEGF-R1 and -R2) was significantly downregulated during structural luteolysis (after 12 hr). VEGF protein concentration already significantly declined 2 hr after PGF2alpha. Surprisingly FGF-1 and FGF-2 were significantly and maximally upregulated during functional luteolysis (until 12 hr). Furthermore, FGF-R mRNA was significantly upregulated at 2 hr after PGF2alpha, when compared with the control group. During structural luteolysis, the expression of FGFs and their receptors was not significantly different from control, except FGF-2 mRNA, which was downregulated at 64 hr. We conclude that the cessation of VEGF-support for the CL plays a role during structural luteolysis, whereas FGFs seem to have a major impact on functional luteolysis. The possible role of these growth factors could be a transient counter-regulation of luteolysis, but also an involvement in preventing inflammatory reactions during luteal regression.

In vivo regulation of mRNA expression of vascular endothelial growth factor receptors (KDR and flt-1) in the human oviduct

OBJECTIVE

To examine the localization of vascular endothelial growth factor receptors (VEGF-R) and the changes in VEGF-R messenger ribonucleic acid (mRNA) expression in various regions of the oviduct from fertile women throughout the ovulatory cycle.

DESIGN

Prospective observational study.

SETTING

University-based obstetrics and gynecology department.

PATIENT(S)

Twenty-two women who underwent laparoscopic tubal sterilization or hysterectomy for a benign gynecological condition.

INTERVENTION(S)

The mucosal layer was isolated from the oviduct tissue. Immunohistochemistry and a semiquantitative reverse-transcriptase-polymerase chain reaction (RT-PCR) was performed.

MAIN OUTCOME MEASURE(S)

Immunohistochemical localization of VEGF-R proteins in oviduct tissue, and the differences of VEGF-R mRNA expression in the various regions of the oviduct and in the various stages of the ovulatory cycle.

RESULT(S)

Immunohistochemical study localized VEGF-R, both KDR and flt-1, in the oviduct luminal epithelium, smooth muscle cells as well as blood vessels within the oviduct. Messenger RNA expression of KDR, but not flt-1, was significantly higher in the ampullary and infundibular regions than in the isthmus. Messenger RNA expression of flt-1, but not KDR, varied significantly in the oviduct along the course of an ovulatory cycle, with the highest level in the periovulatory stage.

CONCLUSION(S)

These results suggest that the two VEGF receptors may have different roles in the oviduct. Our data support a role for KDR in oviduct angiogenesis whereas flt-1 appears to be important in the temporal regulation of oviductal secretion.

Embryo-maternal communication in bovine - strategies for deciphering a complex cross-talk

Early embryonic development, implantation and maintenance of a pregnancy are critically dependent on an intact embryo-maternal communication. So far, only few signals involved in this dialogue have been identified. In bovine and other ruminants, interferon tau is the predominant embryonic pregnancy recognition signal, exhibiting antiluteolytic activity. However, this is just one aspect of the complex process of embryo-maternal signalling, and a number of other systems are more likely to be involved. To gain a more comprehensive understanding of these important mechanisms, integrated projects involving specialists in embryology, reproductive biotechnology and functional genome research are necessary to perform a systematic analysis of interactions between pre-implantation stage embryos and oviduct or uterine epithelial cells, respectively. State-of-the-art transcriptomic and proteomic technologies will identify reciprocal signals between embryos and their maternal environment and the respective downstream reaction cascades. For in vivo studies, the use of monozygotic twins as recipient animals provides elegant model systems, thus eliminating genetic variability as a cause of differential gene expression. In addition, suitable systems for the co-culture of oviduct epithelial or endometrium cells with the respective embryonic stages need to be established for functional validation of candidate genes potentially involved in the dialogue between embryos and their maternal environment. The knowledge of these mechanisms should help to increase the pregnancy rate following embryo transfer and to avoid embryonic losses. Candidate genes involved in embryo-maternal communication will also be used to define new quality criteria for the selection of embryos for transfer to recipients. Another application is the supplementation of embryotrophic factors or components of embryo-maternal signalling in optimized formulations, such as bioartificial matrices. As a long-term goal, signalling mechanisms identified in bovine will also be functionally evaluated in other species, including the human.

Vascular endothelial growth factor in the human oviduct: localization and regulation of messenger RNA expression in vivo

In this study, we examined the localization of vascular endothelial growth factor (VEGF) and the changes in VEGF mRNA expression in various regions of the oviduct in fertile women throughout the ovulatory cycle. Oviduct tissue was collected from 22 women undergoing laparoscopic tubal sterilization or hysterectomy for a benign gynecological condition. Oviduct sections were divided into isthmus, ampullary, and infundibular regions. Serial cross sections were analyzed for the presence of VEGF by specific immunohistochemical staining. The mucosal layer was isolated, and a semiquantitative reverse transcription polymerase chain reaction was performed. Immunohistochemical study revealed VEGF in the oviduct luminal epithelium, smooth muscle cells, and blood vessels within the oviduct. VEGF mRNA expression in oviduct was the highest during the periovulatory stage, and the expression in the ampullary and infundibular regions was higher than that in the isthmus. There was a significant positive correlation between serum FSH and LH concentrations and VEGF mRNA expression. There was no significant correlation between serum estradiol and progesterone concentrations and VEGF mRNA expression. These results suggest that VEGF in human oviduct may play an important role related the early reproductive events, which occur predominantly in the ampulla during the periovulatory phase when serum FSH and LH concentrations are high.

Vascular endothelial growth factor (VEGF) promotes the early development of bovine embryo in the presence of cumulus cells

Three experiments were conducted to determine the effect of Vascular Endothelial Growth Factor (VEGF) on bovine embryonic development in vitro. Human recombinant VEGF(165) was employed at 5 ng/ml in modified synthetic oviduct fluid. In Exp. 1, bovine cumulus oocyte complexes were matured with or without VEGF for 22 hr, inseminated without VEGF for 6 hr, then cultured with or without VEGF for 42 hr. The cleavage rate and the development rate to 4- to 8-cell were higher (P<0.05) in groups with VEGF during in vitro maturation (IVM, 71.4% and 59.6%), in vitro culture (IVC, 70.3% and 62.3%), and both IVM and IVC (75.9% and 67.8%) than in the group cultured thoroughly without VEGF (49.9% and 38.4%, respectively). In Exp. 2, 4- to 8-cell embryos produced in vitro without VEGF were removed from cumulus cells at 48 hr post-insemination (Pi) and cultured with or without VEGF for 144 hr. The development rates to blastocyst at 96 hr (D6), 120 hr (D7) and 144 hr (D8) were similar (P>0.05) in both groups. In Exp. 3, cumulus cells were removed from presumptive embryos produced by IVM and IVF without VEGF at 10 hr Pi. Denuded embryos were cultured with or without VEGF for 38 hr or 182 hr. The cleavage rate and the development rates to 4- to 8-cell at 48 hr Pi and to blastocyst on D6, D7 and D8 were similar (P>0.05) in all groups. These results suggest that VEGF has a beneficial effect on the initial development of bovine embryo through surrounding cumulus cells.

Effect of vascular endothelial growth factor on maturation, fertilization and developmental competence of bovine oocytes

To examine the effect of Vascular Endothelial Growth Factor (VEGF) on the maturation of bovine oocytes, human recombinant VEGF(165) was used in 3 experiments. In Exp. 1, bovine cumulus oocyte complexes (COCs) were matured for 22 hr in modified Synthetic Oviduct Fluid (m-SOF) supplemented with 0 (control) or 5 ng/ml of VEGF. Maturation rate increased (P<0.05) from 78.2% in the control to 90.5% in the VEGF treated group. In Exp. 2, bovine COCs were matured in m-SOF and co-incubated with sperm in modified BO medium, each supplemented with or without 5 ng/ml VEGF. Normal fertilization rate was improved (P<0.05) from 63.0% (control) to 79.8% or 82.3% with VEGF during maturation or both maturation and fertilization. In Exp. 3, bovine COCs were matured the same way as in Exp. 1, then co-incubated with sperm for 6 hr and cultured for 162 hr in m-SOF without VEGF. Cleavage rate and development rate to the 4- to 8-cell stage were examined at 42 hr post-co-incubation and development rate to blastocyst was examined at 162 hr post-co-incubation. Cleavage, the development to the 4- to 8-cell stage and blastocyst rates (82.0%, 70.3% and 45.1%, respectively) were significantly higher (P<0.05) in the VEGF group than those in the control (67.3%, 52.5% and 33.3%, respectively). These results indicate that VEGF has a beneficial effect on the maturation of bovine oocytes.

Expression of the vascular endothelial growth factor and its receptors and effects of VEGF during in vitro maturation of bovine cumulus-oocyte complexes (COC)

A complete VEGF system consisting of the ligand and two of its receptors has been detected for the first time in the bovine cumulus-oocyte-complex (COC). In the course of a 24 hr in vitro maturation procedure (IVM), expression of the smaller VEGF transcripts and their specific receptors flt and flk changed remarkably in a time-dependent manner as observed by RT-PCR. The transcript concentrations of VEGF declined within 24 hr of culture, whereas both receptor mRNAs were found enriched between 6 and 12 hr of IVM. In the follicular fluid of growing ovarian follicles, immunoreactive VEGF, measured by RIA, increased significantly, reaching highest concentrations immediately before ovulation of the oocyte. The immunohistochemical localization of VEGF in bovine COCs revealed strong signals within the cumulus cell complex clearly extending beyond the oocyte cytoplasm at the beginning of in vitro maturation. After 24 hr, IVM immunoreactive VEGF disappeared remarkably from cumulus cells and the oocyte cytoplasm. An exogenous application of VEGF at the beginning of a 24 hr IVM significantly improved cleavage rates of zygotes and their development into bovine embryos showing obvious synergistic effects in combination with FSH, when compared with untreated control embryos. In addition, the number of blastomeres in deriving blastocysts increased after VEGF supplementation. These results indicate a functional VEGF system controlling important events beside the known angiogenetic effect during in vivo and in vitro maturation of the bovine COC, possibly affecting the early embryonic viability.

Early developing embryos affect the gene expression patterns in the mouse oviduct

Fertilization and development of mouse embryos occur in the ampullae of oviduct. We hypothesize that fetal-maternal communication exists in the preimplantation period, allowing optimal development of embryos. It is known that embryotrophic factors from oviduct affect the development of embryos. Although embryos affect their own transport in the oviduct, the mechanism of action is unknown. As a step toward understanding the action of embryos on oviductal physiology, we adopted suppression subtractive hybridization (SSH) to compare the gene expression in the mouse oviduct containing early embryos with that of oviduct containing oocytes. Ten to twelve 1-cell mouse embryos were transferred to one oviduct of a foster mother and similar number of oocytes were transferred to the contralateral oviduct. The animals were sacrificed after 48 h and their oviducts were excised for mRNA study. Using SSH, we screened out 250 putative positive clones from the subtracted embryo-containing oviduct library and 97 of them were screened positive by reverse dot-blot analysis. DNA sequence analysis identified genes that shared high homology with sequences in GenBank/EMBL database with unknown functions. Overall, 13 of the 90 high-quality sequences (14%) were homologous to 6 different genes previously described. Reverse Northern analysis confirmed that the expression of these genes were higher in the embryo-containing oviduct than in the oocyte-containing oviduct. About 12% of these clones (11/90) were novel. This article is the first to report identification of genes in the oviduct that are upregulated in the presence of embryos during the preimplantation period.

Expression and localization of IGF family members in bovine antral follicles during final growth and in luteal tissue during different stages of estrous cycle and pregnancy

The objectives of the study were to monitor the detailed pattern for mRNA expression (RT-PCR and RPA) of IGFs, IGFR-1, IGFBPs, GHR and localization of protein (immunohistochemistry) for IGF-1 and IGFR-1 in bovine follicle classes during final maturation and different corpus luteum (CL) stages during estrous cycle and during pregnancy. A relative high expression of IGF-1 in theca interna (TI) was observed before selection (E<0.5ng/mL). In GC, mRNA expression increased after selection. In contrast, IGF-2 was mainly expressed in the TI. The IGFR-1 mRNA was present in the TI and GC with increasing levels during final development. The expression results were confirmed by localization of IGF-1 and IGFR-1 proteins in GC and TI. There is clear evidence for the local expression of IGFBPs in TI and GC compartment with clear regulatory differences. In CL, the highest mRNA expression of IGF-1, IGF-2 and IGFR-1 was observed during early luteal phase, followed by a decrease, and then by a tendency of an increase during the mid and late luteal phases of the cyclic CL. This level remained low during pregnancy. Intense immunostaining for IGFR-1 in CL was observed mainly in large luteal cells. Evidence for a mRNA for all six IGFBPs were obtained with distinct differences for BP-3, -4 and -5. In conclusion, this comprehensive study gives clear evidence for an important role of the IGFs and IGFBPs in bovine follicular development and CL function. The relative amounts of IGFBPs may ultimately determine ovarian IGF action.

Suppression subtractive hybridization identifies genes expressed in oviduct during mouse preimplantation period

Fertilization and development of mouse embryos occur in the ampullae of oviduct. Various growth factors and embryotrophic factors produced by the oviductal cells have been demonstrated to enhance embryo development in vitro. As a step towards understanding the genetic changes of mouse oviduct during mouse embryos preimplantation period, we adopted suppression subtractive hybridization (SSH) to establish four subtracted cDNA libraries to identify (1) oviduct-expressing genes, and (2) genes that may support embryo development in vivo. Using this method, we isolated 82, 88, 99, and 109 clones from four mouse libraries prepared from 0 (day 0), 24 (day 1), 48 (day 2), and 72 h (day 3) post-human chorionic gonadotropin (hCG) treated mice. Reverse dot-blot analysis confirmed that 25 (day 0), 24 (day 1), 40 (day 2), and 29 (day 3) clones were highly expressed in mouse oviduct when compared to other tissues. DNA sequence analysis identified genes encoding mouse oviduct-specific glycoprotein (MOGP), actin-binding protein 280, and several viral genes. Northern analysis confirmed that the genes were mainly expressed in oviduct, with some viral genes also expressed in uterus. About 9% of these oviduct expressing clones (11/118) were novel. We further demonstrated that one of the novel clones ODEG0-17 was expressed in the oviduct during early embryo preimplantation period and rarely in other tissues by RT-PCR. Our results show that SSH is a powerful method applicable to identifying tissue-specific transcripts on fertilization and development.

Expression and tissue concentration of vascular endothelial growth factor, its receptors, and localization in the bovine corpus luteum during estrous cycle and pregnancy

The presence of vascular endothelial growth factor (VEGF) in the ovary has been reported in a number of species. The objective of the present study was to demonstrate the expression of VEGF, VEGF receptor (R)-1, and VEGFR-2 in detail by different methodological approaches in bovine corpora lutea (CL) obtained from different stages of the estrous cycle and during pregnancy. VEGF and VEGF receptor transcripts were analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and ribonuclease protection assay. All components of the VEGF system were found in the bovine CL during the estrous cycle and pregnancy. Analysis of VEGF transcript by RT-PCR shows that CL tissues expressed predominantly the smallest isoforms (VEGF(121) and VEGF(165)). The highest mRNA expression for VEGF and VEGFR-2 mRNA was detected during the early luteal phase, followed by a significant decrease of expression during the mid and late luteal phase and a further decrease of VEGF mRNA after regression. During pregnancy, high levels of expression were always present. In contrast, no significant change in VEGFR-1 mRNA expression during the estrous cycle and pregnancy was found. The VEGF protein concentration in CL tissue was significantly higher (20.9-23.4 ng/g wet weight) during the early luteal phase (Days 1-7), followed by a decrease at the late luteal phase (14.3-18.7 ng/g wet weight) and, especially, after CL regression (2.8 ng/g wet weight). However, relatively high levels were found during pregnancy (10.1 ng/g wet weight). As achieved by immunohistochemistry, VEGF protein was localized predominantly in luteal cells. High VEGF protein and transcript concentrations and increased VEGFR-2 expression during the early luteal phase coincided with luteal vascularization. These results suggest an important role of VEGF in angiogenesis of the newly formed CL. The high VEGF mRNA expression and protein levels during matured vasculature in the mid-stage CL and pregnancy also suggest also a survival function for endothelial cells.