In situ localization of messenger ribonucleic acid for an oviduct-specific glycoprotein during various hormonal conditions in the golden hamster

The role of oviduct-specific glycoprotein (OVGP1) in modulating biological functions of gametes and embryos

Diverse lines of evidence indicate that the mammalian oviduct makes important contributions to the complex process of reproduction other than being simply a conduit for the transport of gametes and embryos. The cumulative synthesis and transport of proteins secreted by oviductal secretory cells into the oviductal lumen create a microenvironment supporting important reproductive events, including sperm capacitation, fertilization, and early embryo development. Among the components that have been identified in the oviductal fluid is a family of glycosylated proteins known collectively as oviduct-specific glycoprotein (OVGP1) or oviductin. OVGP1 has been identified in several mammalian species, including humans. The present review summarizes the work carried out, in various mammalian species, by many research groups revealing the synthesis and secretion of OVGP1, its fate in the female reproductive tract upon secretion by the oviductal epithelium, and its role in modulating biological functions of gametes and embryos. The production and functions of recombinant human OVGP1 and recombinant OVGP1 of other mammalian species are also discussed. Some of the findings obtained with immunocytochemistry will be highlighted in the present review. It is hoped that the findings obtained from recent studies carried out with recombinant OVGP1 from various species will rekindle researchers’ interest in pursuing further the role of the oviductal microenvironment, of which OVGP1 is a major component, in contributing to the successful occurrence of early reproductive events, and the potential use of OVGP1 in improving the current assisted reproductive technology in alleviating infertility.

A Comparative View on the Oviductal Environment during the Periconception Period

The oviduct plays important roles in reproductive events: sperm reservoir formation, final gamete maturation, fertilization and early embryo development. It is well known that the oviductal environment affects gametes and embryos and, ultimately, the health of offspring, so that in vivo embryos are better in terms of morphology, cryotolerance, pregnancy rates or epigenetic profile than those obtained in vitro. The deciphering of embryo-maternal interaction in the oviduct may provide a better understanding of the embryo needs during the periconception period to improve reproductive efficiency. Here, we perform a comparative analysis among species of oviductal gene expression related to embryonic development during its journey through the oviduct, as described to date. Cross-talk communication between the oviduct environment and embryo will be studied by analyses of the secreted or exosomal proteins of the oviduct and the presence of receptors in the membrane of the embryo blastomeres. Finally, we review the data that are available to date on the expression and characterization of the most abundant protein in the oviduct, oviductin (OVGP1), highlighting its fundamental role in fertilization and embryonic development.

Effects of recombinant OVGP1 protein on in vitro bovine embryo development

Previously, our group demonstrated that recombinant porcine oviductin (pOVGP1) binds to the zona pellucida (ZP) of in vitro-matured (IVM) porcine oocytes with a positive effect on in vitro fertilization (IVF). The fact that pOVGP1 was detected inside IVM oocytes suggested that this protein had a biological role during embryo development. The aim of this study was to evaluate the effects of pOVGP1 on bovine in vitro embryo development. We applied 10 or 50 µg/ml of pOVGP1 during IVF, embryonic in vitro culture (IVC), or both, to evaluate cleavage and embryo development. Blastocyst quality was assessed by analyzing the expression of important developmental genes and the survival rates after vitrification/warming. pOVGP1 was detected in the ZP, perivitelline space, and plasma membrane of blastocysts. No significant differences (P > 0.05) were found in cleavage or blastocyst yield when 10 or 50 µg/ml of pOVGP1 was used during IVF or IVC. However, when 50 µg/ml pOVGP1 was used during IVF + IVC, the number of blastocysts obtained was half that obtained with the control and 10 µg/ml pOVGP1 groups. The survival rates after vitrification/warming of expanded blastocysts cultured with pOVGP1 showed no significant differences between groups (P > 0.05). The use of pOVGP1 during IVF, IVC, or both, increased the relative abundance of mRNA of DSC2, ATF4, AQP3, and DNMT3A, the marker-genes of embryo quality. In conclusion, the use of pOVGP1 during bovine embryo in vitro culture does not affect embryo developmental rates but produces embryos of better quality in terms of the relative abundance of specific genes.

Expression and localization of gonadotropin-releasing hormone receptor in the rat oviduct during pregnancy

A recent study from our laboratory has shown cellular and ultrastructural distribution of the gonadotropin-releasing hormone (GnRH) and the relative expression of its mRNA in the rat oviduct during the postimplantation period of pregnancy (days 7, 9, 16, and 20). To determine the possible autocrine/paracrine involvement of the oviductal GnRH during pregnancy in rats, the present investigation aims at the study of the relative expression of GnRH receptor (GnRHR) mRNA by real-time PCR followed by immunolocalization of the peptide in the oviduct during pregnancy. Semiquantitative analysis of the oviductal GnRHR expression by Western blot was done by densitometry of the signal intensity. Our results indicate the expression of GnRHR mRNA in the rat oviduct throughout the postimplantation period of pregnancy with no significant difference in expression between the selected time points. Immunoreactive GnRHR peptide was localized predominantly in the cytoplasm of the luminal epithelial cells, with less expression in the cytoplasm of the stromal cells and the smooth muscles throughout the oviduct. Signal intensity of GnRHR was significantly lower during day 16 when compared to days 7 and 20. These results, for the first time, support the transcription of GnRHR mRNA and its translation to protein in the rat oviduct throughout the postimplantation period of pregnancy. The lower protein content of GnRHR by day 16 may be indicative of ligand-induced downregulation of the receptor expression. The present investigation thus strengthens our previously postulated hypothesis regarding the receptor-mediated autocrine/paracrine role of oviductal GnRH during pregnancy in rats.

Localization of immunoreactive gonadotropin-releasing hormone and relative expression of its mRNA in the oviduct during pregnancy in rats

This study was designed to determine the cellular and ultrastructural distribution of the gonadotropin-releasing hormone (GnRH) and the relative expression of its mRNA in the oviduct of rats during different time points (days 7, 9, 16, and 20) of pregnancy. Immunofluorescent localization and confocal microscopic techniques were used to determine the cellular distribution of GnRH in the oviduct. Immunogold electron microscopy indicated its localization at the ultrastructural level, and real-time PCR was used to study the expression pattern of GnRH mRNA in the oviduct during pregnancy. In general, GnRH was localized within the epithelial cells lining the oviductal lumen at each selected time point. A strong correlation between the fluorescence intensity of GnRH-immunoreactive cells and the relative expression of GnRH mRNA was noted on days 7 and 16, followed by a plateau by day 20. At the ultrastructural level, uniform labeling of colloidal gold particles was observed in secretory vesicles and lamella of the luminal epithelium as well as the lumen of the oviduct. Collectively, these results demonstrate for the first time that the oviductal epithelium synthesizes and secretes the decapeptide GnRH during pregnancy in rats, which may have a possible role in postimplantation embryonic development and the maintenance of pregnancy.

Characterization of an immortalized oviduct cell line from the cynomolgus monkey (Macaca fascicularis)

To establish reproductive biological techniques in mammals, it is important to understand the growth environment of the embryo. Oviduct epithelial cells are in close proximity to the embryo during pre-implantation development. We, therefore, established an immortalized oviduct epithelial cell line from the cynomolgus monkey, evaluated the usefulness of these cells as feeder cells for embryo culture, and investigated the gene expression of several growth factors and cytokines in the cells. The immortalized cells were positive for the anti-cytokeratin antibody, as determined by immunocytochemistry, indicating that they are epithelial. They also expressed oviductin, which is specific to oviduct epithelial cells, glyceraldehyde-3-phosphate dehydrogenase (control), leukemia inhibitory factor, vascular endothelial growth factor, epidermal growth factor, insulin-like growth factor 1, transforming growth factor beta-2, and interleukin 4. Mouse embryo development was improved when the immortalized cells were used as feeder cells. This cell line is also useful for studying the factors secreted by oviduct epithelial cells.

Evidence for the Regulation of Glycosylation of Golden Hamster (Mesocricetus auratus) Oviductin During the Estrous Cycle1

The oviduct contributes to the reproductive environment by secreting various factors, including a family of glycoproteins termed oviductins. Although many studies have demonstrated that ovarian hormones modulate oviductin gene expression in several mammalian species, there has been controversy surrounding the regulation of golden hamster oviductin. The current study was undertaken to investigate the transcriptional and translational modifications of hamster oviductin during the estrous cycle. First, we verified that hamster oviductin mRNA expression remains constant throughout the estrous cycle by semiquantitative reverse transcription polymerase chain reaction. We then developed a polyclonal antibody against recombinant hamster oviductin (rhaOvm). The anti-rhaOvm antibody was subsequently used in conjunction with quantitative immunocytochemistry to investigate the oviductin levels in the hamster oviduct during the estrous cycle. Quantification of immunolabeling revealed a high, consistent level of glycoprotein throughout the estrous cycle. Therefore, it appears that the production of oviductin is not regulated differentially during the estrous cycle. Size variations in hamster oviductin expression were also investigated by Western blot analysis. The oviduct contains several forms of oviductin at each stage of the estrous cycle, the native glycosylated form(s) of 160-350 kDa, and several precursor forms of 70-100 kDa. Although variations in the intensities of the polydispersed band were not evident during the estrous cycle, additional bands ranging from 90 to 100 kDa were detected in the estrus, metestrus, and diestrus 1 stages. The results from the present investigations suggest that whereas ovarian hormones do not appear to influence the hamster oviductin mRNA and protein expressions, glycosylation of hamster oviductin appears to be differentially regulated during the estrous cycle.

Effect of a null mutation of the oviduct-specific glycoprotein gene on mouse fertilization

The mammalian fertilization process takes place in a complex microenvironment within the female genital tract. A member of the chitinase protein family, oviduct-specific glycoprotein (OGP), has been identified in oviductal fluid from various mammalian species, including humans. Although OGP is widely believed to be involved in the process of mammalian fertilization, including spermatozoon function and gamete interactions, based on experimental results obtained in vitro, its physiological significance remains controversial. The present study established OGP gene-null ( ogp (-/-)) mice, and primarily characterized their reproductive properties to study the physiological function(s) of OGP. Results obtained from studies using an in vivo or in vitro system showed that the fertility of ogp (-/-) females was within normal limits. These results indicate that OGP is not essential for the process of in vivo fertilization, at least in mice.

Overexpression of monkey oviductal protein: purification and characterization of recombinant protein and its antibodies

The secretory cells lining the lumen of the mammalian oviduct synthesize and secrete high molecular weight glycoprotein (OGP). Molecular cDNA cloning of most of the mammalian OGP has been accomplished. The nucleotide and deduced amino acid sequences show a remarkable homology across species and also to chitinase protein. Even though OGP has been shown to interact with gametes and the early embryo, the protein's direct function has not yet been established. A prerequisite for such studies is the availability of well-characterized protein in bulk. We used recombinant DNA technology to obtain OGP (rOGP). An authentic partial cDNA clone encoding bonnet monkey (Macaca radiata) OGP (accession number AF132 215) was recloned into expression vector pET20b. Overexpression of the protein could be demonstrated after induction with isopropylthio-beta-galactopyranoside. Recombinant protein was purified by gel filtration of Escherichia coli lysate through Sephadex G75. The protein migrated with a molecular weight of approximately 14 kDa on SDS-PAGE. The molecular weight as assessed by matrix-assisted laser adsorption time-of-flight was 14 439 daltons. With Western blot procedures the protein could be immunostained with antibodies to human OGP, baboon OGP, and antipeptide antibodies generated against a well-conserved region of mammalian OGP. The monospecificity of rabbit antibodies generated against rOGP was established by its ability to immunostain human OGP (100-110 kDa) isolated from hydrosalpinx by Western blot analysis, and the antibody immunostained epithelial cells that secrete OGP in human fallopian tubes. OGP binding sites on the head and tail region of monkey sperm could be demonstrated by using antibody against rOGP.

Variable expression of oviductin mRNA at different stages of human reproductive cycle

PURPOSE

To examine the in vivo expression of oviductin mRNA at different stages of the human female reproductive cycle including pregnancy and after menopause.

METHODS

Oviducts were obtained from 25 women in normal menstrual cycle, 5 in early pregnancy, 5 undergoing postpartum sterilization, and 4 menopausal women. The oviductal mucosal tissue was isolated and oviductin mRNA was assessed using reverse-transriptase-polymerase chain reaction (RT-PCR); its correlation with various hormones was assessed.

RESULTS

Oviductin mRNA was detected throughout the menstrual cycle, highest in the periovulatory period. It continued to be expressed in early pregnancy but was absent in the postpartum period and after menopause.

CONCLUSIONS

The production and function of oviductin at different stages of human reproductive cycle including pregnancy is not well known. Its highest expression at the time of ovulation is consistent with a supportive role in fertilization and early embryo development.

Organization of a gene coding for an oviduct-specific glycoprotein (oviductin) in the hamster

Hamster oviductin, a high molecular weight glycoprotein secreted by the oviducts, is believed to participate in fertilization and protection of the tubal epithelium. Expression of the oviductin gene is confined strictly to nonciliated secretory cells of the oviduct and is regulated by hormones. The objective of this study was to characterize the genomic organization and to identify potential regulatory elements implicated in the control of transcription of the oviductin gene. Polymerase chain reaction was performed on hamster genomic DNA, yielding 2.2 kb of the 5' flanking region as well as 13.6 kb of genomic sequence comprising the entire coding sequence of the oviductin gene distributed in 11 exons. Sequencing of the 5' flanking region revealed, among other elements, an almost perfect estrogen-responsive element (GGTCACTGTGACT), an atypical TATA box (TATTAA), and a perfect inverted Sp1 site located between the transcription start site and the atypical TATA box. Primer extension analyses indicated that the hamster oviductin transcript possesses an unusually short 5' untranslated region of only 14 nucleotides. The distinct organization of the hamster oviductin gene in the vicinity of the transcription start site provides an interesting ground for further functional studies.

Rat zona pellucida glycoproteins: molecular cloning and characterization of the three major components

The zona pellucida (ZP), the extracellular glycocalyx that surrounds the oocyte, is well known to mediate homologous gamete interaction. In a previous study from our laboratories, we reported the qualitative characterization of the rat ZP. The ZP in this species, like the mouse, hamster, and human, was found to contain three glycoproteins, namely rZP1, rZP2, and rZP3 (Araki et al. [1992] Biol Reprod 46:912-919). In this study, cDNAs encoding whole rat ZP major components have been isolated and characterized. A rat ovary cDNA library was screened with the mouse ZP3 and ZP2 cDNA probes, respectively. For rZP1 cDNA cloning, cDNAs generated using reverse transcriptase-polymerase chain reaction and rapid amplification of 5' and 3' cDNA ends, were isolated and sequenced. The rZP3 cDNA showed 1338 bp with a coding region containing 1272 bp, that translates into 424 amino acids. The total translation of rZP3 peptide has a molecular weight of 45,820, containing six potential N-glycosylation sites and 75 Ser/Thr residues, possible O-glycosylation sites. The amino acid sequence derived from the cDNA sequence shares high sequence homologies to mouse (90%), hamster (78%), and human (65%) ZP3 (ZPC) glycoproteins, indicating that the rat and mouse ZP3 have quite a conserved amino acid sequence, including the potential glycosylation sites. The total transcript of the rZP2 was 2154 nucleotides and the largest open reading frame was 695 amino acids. This would translate into a protein of 78.4 kDa. In the case of rZP1, the cDNA clone consisted of 1960 bp, and the coding region contained 1851 bp translating into 617 amino acids. Significant homologies were observed between rZP2 and ZPA family from various mammalian species. The rZP1 also showed a sequence homology to mouse ZP1, known as a mouse orthologue of ZPB family, suggesting that the rZP2 and rZP1 are members of ZPA and ZPB families, respectively. The message distributions for each zona components were limited within the ovary and the signal was detectable in the growing oocytes. The present results will further our understanding of the structure of rat zona components and lead to a better understanding of species-specificity observed during sperm-egg interaction.

A novel regulation of the oviductal glycoprotein gene expression by luteinizing hormone in bovine tubal epithelial cells

The hypothesis that bovine oviductal epithelial cells contain luteinizing hormone (LH)/human chorionic gonadotropin (hCG) receptors and LH may regulate the oviductal glycoprotein (OGP) gene expression was tested. The results showed that bovine oviductal epithelial cells contain an 80 kDa LH/hCG receptor protein which can bind [(125)I]hCG. Culturing these cells with highly purified hCG, used as a surrogate hormone for LH, resulted in a dose and time dependent increase in a 95 kDa protein and a 2.3 kb transcript of OGP. The maximal increase of 100% was obtained with 10 ng/ml hCG and after three days of culture. LH, but not other hormones in the glycoprotein hormone family, isolated subunits of hCG, estradiol-17beta or progesterone, mimicked hCG, suggesting that the effect is hormone specific and requires the conformation of native hormone. The increase in steady state OGP mRNA levels by hCG is not due to an increase in the transcription rate of the gene. It is rather due to a significant increase in the half-life of OGP transcripts from 23 h in the control to 28 h after treatment with hCG. In summary, we conclude that LH and hCG can increase the synthesis of OGP by decreasing the degradation of its transcripts in bovine oviductal epithelial cells. Since OGP may play important roles in fertilization and growth and development of early embryo, higher LH levels present during the periovulatory period may directly participate in the early pregnancy events through increasing the synthesis of OGP.