Fate of hamster oviductin in the oviduct and uterus during early gestation

The fluid factor OVGP1 provides a significant oviductal microenvironment for the reproductive process in golden hamster†

The mammalian oviductal lumen is a specialized chamber that provides an environment that strictly regulates fertilization and early embryogenesis, but the regulatory mechanisms to gametes and zygotes are unclear. We evaluated the oviductal regulation of early embryonic development using Ovgp1 (encoding an oviductal humoral factor, OVGP1)-knockout golden hamsters. The experimental results revealed the following: (1) female Ovgp1-knockout hamsters failed to produce litters; (2) in the oviducts of Ovgp1-knockout animals, fertilized eggs were sometimes identified, but their morphology showed abnormal features; (3) the number of implantations in the Ovgp1-knockout females was low; (4) even if implantations occurred, the embryos developed abnormally and eventually died; and (5) Ovgp1-knockout female ovaries transferred to wild-type females resulted in the production of Ovgp1-knockout egg-derived OVGP1-null litters, but the reverse experiment did not. These results suggest that OVGP1-mediated physiological events are crucial for reproductive process in vivo, from fertilization to early embryonic development. This animal model shows that the fate of the zygote is determined not only genetically, but also by the surrounding oviductal microenvironment.

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.

Oviductal glycoprotein 1 (OVGP1) is expressed by endometrial epithelium that regulates receptivity and trophoblast adhesion

PURPOSE

To study the regulation and functions of oviductal glycoprotein 1 (OVGP1) in endometrial epithelial cells.

METHODS

Expression of OVGP1 in mouse endometrium during pregnancy and in the endometrial epithelial cell line (Ishikawa) was studied by immunofluorescence, Western blotting, and RT-PCR. Regulation of OVGP1 in response to ovarian steroids and human chorionic gonadotropin (hCG) was studied by real-time RT-PCR. OVGP1 expression was knockdown in Ishikawa cells by shRNA, and expression of receptivity associated genes was studied by real-time RT-PCR. Adhesion of trophoblast cell line (JAr) was studied by in vitro adhesion assays.

RESULTS

OVGP1 was localized exclusively in the luminal epithelial cells of mouse endometrium at the time of embryo implantation. Along with estrogen and progesterone, hCG induced the expression of OVGP1 in Ishikawa cells. Knockdown of OVGP1 in Ishikawa cells reduced mRNA expression of ITGAV, ITGB3, ITGA5, HOXA10, LIF, and IL15; it increased the expression of HOXA11, MMP9, TIMP1, and TIMP3. Supernatants derived from OVGP1 knockdown Ishikawa cells reduced the adhesiveness of JAr cells in vitro. Expression of OVGP1 mRNA was found to be significantly lowered in the endometrium of women with recurrent implantation failure.

CONCLUSION

OVGP1 is specifically induced in the luminal epithelium at the time of embryo implantation where it regulates receptivity-related genes and aids in trophoblast adhesion.

Detection of nascent and/or mature forms of oviductin in the female reproductive tract and post-ovulatory oocytes by use of a polyclonal antibody against recombinant hamster oviductin

Oviductins belong to a family of glycoproteins that have been suggested to play several roles during the early processes of reproduction. Recently, a polyclonal antibody was raised against recombinant hamster oviductin (rhaOv(m)). Here the anti-rhaOv(m) antibody was used to investigate the sites of localization of oviductin in the female golden hamster. In the hamster oviduct, immunolabeling was restricted to the content of the Golgi saccules and secretory granules of the non-ciliated oviduct cells. After its release into the lumen, oviductin becomes associated with the zona pellucida of post-ovulatory oocytes. In unfertilized oocytes, oviductin was also detected in membrane invaginations along the oolemma and in some vesicles within the ooplasm. Furthermore, oviductin was detected over the microvilli and within multivesicular bodies of uterine epithelial cells. Western blotting analysis revealed the presence of oviductin in the hamster oviduct but not in the uterus or ovary. In the oviduct, the anti-rhaOv(m) antibody detected a polydispersed band corresponding to native oviductin (160-350 kD) and several lower molecular weight bands (<100 kD) corresponding to nascent and partially glycosylated forms of oviductin. The anti-rhaOv(m) antibody provides an additional tool for investigation into the cytochemical and biochemical properties of different forms of hamster oviductin in the female reproductive tract.

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.

Mammalian chitinase-like proteins

Mammals express genes coding for proteins that show significant similarity to chitinases of family 18 glycosyl hydrolases. These chitinase-like proteins have no chitinase activity due to changes in critical residues in the putative active center. One of these is oviductin, a high molecular weight glycoprotein most likely involved in fertilization and protection of the tubal epithelium owing to its mucin character. Another is YKL-40 (HCgp39) produced in association with tissue remodeling. Such proteins could have a general function in morphogenesis.

Immunohistochemical localization of oviductin in the endometrial lining of the golden hamster (Mesocricetus auratus) during the estrous cycle and early gestation

Oviductal non-ciliated secretory epithelial cells, under hormonal stimulation, synthesize and secrete a family of glycoproteins referred to as oviductins. These glycoproteins are found in oviductal fluid in several mammalian species, and have been localized in the oviduct, and in the zona pellucida of ovulated oocytes. In the golden hamster, this glycoprotein is named hamster oviductin-I. Recently, an immunofluorescent study on hamster uterine tissue has revealed the presence of the glycoprotein in luminal epithelial cells in a heterogeneous labelling pattern during the estrous cycle. The mechanism of endometrial epithelial cell receptivity to hamster oviductin-1 is not known. In this study, immunohistochemical studies were performed using a monoclonal antibody against the oviductin in conjunction with silver enhancement technique, in an attempt to determine further the factors playing a role in uterine receptivity to oviductin-1. Paraffin sections of hamster uterus obtained from different stages of the estrous cycle and from days 1-6 of gestation, and paraffin sections of hamster oviduct obtained from days 1-6 of gestation were used in this study. The results we obtained using the silver enhancement technique show that hamster uterus luminal epithelial cells exhibit a homogeneous, high intensity immunolabelling pattern throughout the estrous cycle, whereas, during gestation, labelling intensity decreases as the period for blastocyst implantation approaches. Oviduct epithelial cells revealed no definite fluctuating pattern in immunolabelling intensities during gestation, indicating no change in synthesis and secretion of the glycoprotein during this period. It is speculated that receptors for hamster oviductin-1 are present at the apical cell surface of endometrial cells and that implantation of the developing blastocyst into the uterine wall is possible only following downregulation of these receptors. The use of the silver enhancement technique proves to be an effective tool in immunohistochemical studies at the light microscope level, as seen through this study.