Immunological detection of an oviductal glycoprotein in the rat

Modelling oviduct fluid formation in vitro

Oviduct fluid is the microenvironment that supports early reproductive processes including fertilisation, embryo cleavage, and genome activation. However, the composition and regulation of this critical environment remains rather poorly defined. This study uses an in vitro preparation of the bovine oviduct epithelium, to investigate the formation and composition of in vitro derived oviduct fluid (ivDOF) within a controlled environment. We confirm the presence of oviduct specific glycoprotein 1 in ivDOF and show that the amino acid and carbohydrate content resembles that of previously reported in vivo data. In parallel, using a different culture system, a panel of oviduct epithelial solute carrier genes, and the corresponding flux of amino acids within ivDOF in response to steroid hormones were investigated. We next incorporated fibroblasts directly beneath the epithelium. This dual culture arrangement represents more faithfully the in vivo environment and impacts on ivDOF composition. Lastly, physiological and pathophysiological endocrine states were modelled and their impact on the in vitro oviduct preparation evaluated. These experiments help clarify the dynamic function of the oviduct in vitro and suggest a number of future research avenues, such as investigating epithelial-fibroblast interactions, probing the molecular aetiologies of subfertility, and optimising embryo culture media.

In vivo versus in vitro oviductal glycoprotein (OGP) association with the zona pellucida (ZP) in the hamster and baboon

The goal of this study was to determine if differences exist between in vivo vs. in vitro OGP association with the ZP and to quantitate those differences. Ovarian oocytes were harvested 12.5 or 27 hr post-hCG from hyperstimulated hamsters or baboons, respectively. Hamster and baboon ovarian oocytes were incubated in vitro in media +/- homologous OGP (100 or 200 microg/100 microl) or in some studies with 100 microl oviductal fluid for 3, 6, or 24 hr at 37 degrees C. Some of the baboon ovarian oocytes were transferred immediately after harvesting to the ampulla of both oviducts using a tom cat catheter and retrieved after a 3 hr in situ incubation. Hamster oviductal oocytes were collected 3, 6, and 24 hr following ovulation. After incubation or oocyte retrieval from the oviduct, cumulus cells were removed, oocytes were washed extensively and binding of OGP to the ZP was examined by immunofluorescence. Fluorescence intensity was quantified using densitometric scanning of photographic negatives with the background of each negative as an internal control. In all studies, OGP association with the ZP was significantly greater in vivo than in vitro (P < 0.05). In vitro OGP association with the ZP did not significantly increase with incubation time or OGP concentration; however, a small nonsignificant increase in OGP association with the ZP in the oviduct was detected over time. Differences did not appear to be due to depletion of OGP from the in vitro incubation media, since Western blot analysis of the media showed that OGP was still present. Although OGP concentration in vivo is unknown, Western blots showed similar intensity comparing 100 microg of OGP media and oviductal fluid. Immunolocalization of OGP using laser confocal microscopy showed regional differences in OGP binding. The outer half of the zona pellucida had significantly more OGP bound than the inner half on oviductal oocytes. No regional differences were detected for in vitro incubated oocytes. In conclusion, OGP association with the ZP is greater in vivo vs. in vitro, suggesting that one must be cautious in designing and evaluating in vitro studies of OGP function.

Sialomucin complex (Muc4) expression in the rat female reproductive tract

Previous studies in our laboratory demonstrated the presence of sialomucin complex (SMC)/Muc4 covering the rat uterine luminal epithelium. SMC/Muc4 expression in the uterus is regulated by estrogen and progesterone and lost at the time of receptivity. In contrast to this hormonal regulation at the uterine luminal surface, SMC/Muc4 in the uterine glandular epithelium, oviduct, cervix, and vagina was constitutively expressed at all stages of the estrous cycle. Furthermore, SMC was expressed in the cervix and vagina of the ovariectomized rat, even though it is not found in the uterine luminal epithelium. Both soluble and membrane-bound forms of SMC were present in these tissues. Immunohistochemical analyses showed distinctive localization patterns of SMC in the various tissues during the estrous cycle. Moreover, the previously unreported expression of SMC/Muc4 in the isthmus, ampulla, and infundibulum of the oviduct suggests potential functions in gamete development. These results indicate that SMC/Muc4 is expressed in most tissues of the female reproductive tract, in which it may have multiple functions. However, hormonal regulation appears to be restricted to the uterine luminal epithelium.

cDNA sequence and deduced amino acid sequence of bovine oviductal fluid catalase

A bovine oviductal fluid catalase (OFC) which preferentially binds to the acrosome surface of some mammalian spermatozoa has recently been purified. The objectives of this study were to clone the OFC, obtain the full-length cDNA and protein sequence and determine which characteristics of the proteins are associated with the binding of the enzyme to sperm surface. Northern blot analysis revealed low levels of catalase mRNA in bovine oviducts and uterus compared to the liver and kidney. Screening of a cDNA library from the cow oviduct permit to obtain a full-length cDNA of 2282 bp, with an open reading frame of 1581 bp coding for a deduced protein of 526 amino acids (59,789 Da). The deduced protein contained four potential N-glycosylation sites and many potential O-glycosylation sites. The OFC protein exhibited high identity with catalase from other bovine tissues, likewise with catalases from human fibroblast and kidney, and with rat liver catalase. The homology of amino acid sequence of OFC with bovine liver catalase was about 99%. However the OFC possess an extended carboxyl terminus of 20 amino acids not present on the liver catalase. This result is supported by a lower mobility of the OFC compared to the liver catalase when both proteins are submitted on SDS-PAGE.

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.

Bovine oviduct-specific glycoprotein: a potent factor for maintenance of viability and motility of bovine spermatozoa in vitro

In the cow, a specific glycoprotein--bovine oviduct-specific glycoprotein (BOGP)--is secreted by the epithelial cells of the oviduct at the follicular stage of the estrous cycle. In this study, we examined the effects of purified BOGP on the viability and motility of bovine spermatozoa in culture in vitro. Frozen-thawed bovine spermatozoa were incubated in modified Tyrode's solution (TALP) that contained purified BOGP (TALP-BOGP). In TALP-BOGP, both the viability and motility of bovine spermatozoa were more effectively maintained than in the control medium without any added protein. The increases in both the viability and motility of spermatozoa were dose-dependent. Spermatozoa were also incubated in TALP medium supplemented with bovine serum albumin, egg albumin, lactalbumin, or gastric mucin, and their viability and motility in these media were compared with that in TALP-BOGP. Both the viability and motility of spermatozoa were more effectively maintained in TALP-BOGP throughout a 12-hr incubation than in other media tested. An immunolabeling study demonstrated that a monoclonal antibody specific for BOGP reacted with the posterior region of the head, the middle portion, and the tail of spermatozoa that had been incubated with TALP-BOGP, suggesting that BOGP becomes specifically associated with particular regions of the spermatozoon. These results suggest that BOGP is a potent factor for maintenance of the viability and motility of sperm. On the basis of the present results, we also propose that BOGP may play an important role in sperm functions during the reproductive process.

Oviductins possess chitinase- and mucin-like domains: a lead in the search for the biological function of these oviduct-specific ZP-associating glycoproteins

Over the last 10 years considerable progress has been made in the immunological and biochemical characterization of oviduct-specific glycoproteins. It is now well established that a subclass of these secretory products, designated as oviductins, associate with the zona pellucida of the ovulated oocyte and with the early embryo. Recent reports on the cloning of cDNAs of oviductins from various species, including that of golden hamster (Mesocricetus auratus) oviductin by our laboratory, allowed us to compare their deduced amino acid sequences with those of other proteins. Optimal alignment analysis showed that oviductins contain regions of significant similarity with catalytically inactive mammalian members of the bacterial and microfilarial chitinase protein family. Most importantly, a close examination of the hamster and human deduced amino acid sequences revealed that both glycoproteins possess contiguous Ser/Thr rich repeated units, clustered in their carboxy-terminal portions. These mucin-type motifs are similar in the hamster and human glycoprotein, although hamster oviductin contains more of these complete units. This striking feature might indicate that these molecules play a similar role to mucin-type glycoproteins, e.g., in protecting the oocyte and early embryo against attacks from their environment. We propose a model whereby oviductins are targeted to the oocyte via the interaction of their chitinase-like domains with specific oligosaccharide moieties of the zona pellucida. Once localized to this structure, oviductin molecules would act as a protective shield around the oocyte and early embryo by virtue of their densely glycosylated mucin-type domains.

Regional variations in the ultrastructural features of secretory cells in the rat oviductal epithelium

BACKGROUND

In mammals, the oviductal secretory cells and their secretions play important roles in reproductive and developmental events. Therefore, many electron microscopic studies of mammalian oviductal epithelial cells have been performed.

METHODS

The secretory cells in various regions of the rat oviduct during the estrous cycle were examined by transmission electron microscopy.

RESULTS

In the fimbriae, the secretory cells contained small secretory granules with moderately electron-dense matrices and many large bodies that resembled lipid droplets. In the ampullar cells, small secretory granules with moderately electron-dense matrices were observed in the apical cytoplasm. In the isthmus, the secretory cells contained numerous secretory granules with moderately electron-dense matrices. Electron-dense areas were frequently observed in many of the granules of the isthmic cells. Vesicles, partially filled with a dense substance, frequently were observed in the isthmic cells and occasionally in the ampullar cells. Very long stereocilia projected from the surfaces of the isthmic secretory cells into the lumen. Exocytosis of the secretory granules was observed. In addition, there was evidence to suggest the release of the bodies that resembled lipid droplet occurred. Cysts and ciliated vacuoles that appeared to be intraepithelial were frequently observed in the fimbrial and ampullar epithelia. No dramatic changes in the relative numbers of ciliated and secretory cells in any oviductal segment were observed during the estrous cycle.

CONCLUSIONS

Our ultrastructural observations of the rat oviduct revealed marked regional variations in the morphological features of secretory cells. These results may provide insight into regional and cellular differences in the function of the rat oviduct.