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.
Purpose To investigate the effects of recombinant human oviduct–specific glycoprotein (rHuOVGP1) alone and in combination with progesterone (P4) on intracellular Ca2+ concentration [Ca2+]i and to investigate if rHuOVGP1 in combination with P4 can further enhance tyrosine phosphorylation (pY) of sperm proteins during human sperm capacitation. Methods Fluorometric flow cytometry was performed to examine the effects of rHuOVGP1 on [Ca2+]i in human sperm during capacitation. Confocal microscopy was used in conjunction with live cell imaging to analyze the influence of rHuOVGP1 and P4 on [Ca2+]i in the sperm tail and to examine the involvement of CatSper channels in their effect on [Ca2+]i. Western blot analysis was performed to assess the protein levels of p105, a major tyrosine-phosphorylated sperm protein. Results rHuOVGP1 increases [Ca2+]i in human sperm at the beginning of capacitation and further increases and sustains the level of [Ca2+]i in the sperm tail following the addition of P4. Inhibition of CatSper channels impedes the effects of rHuOVGP1 on [Ca2+]i in the sperm tail. P4 alone can increase pY of a major human sperm protein, p105, yet yields a further increase when used in combination with rHuOVGP1. Conclusion The present study revealed that rHuOVGP1 may work with P4 to upregulate [Ca2+]i at the beginning of capacitation in part through CatSper channels which, in turn, leads to the downstream event of pY of sperm proteins and enhancement of sperm capacitation.
Worldwide, around 15% of couples who seek to conceive suffer from infertility. Assisted reproductive technology (ART) would have never been possible without research endeavors. However, to further improve the fertilization rates of ART procedures, there is still more to be done. The mammalian oviductal cells synthesize and secrete a major glycoprotein know as oviductin, or oviduct-specific glycoprotein (OVGP1). This protein has been implicated in enhancing sperm capacitation, sperm motility, sperm penetration and fertilization. Our lab has successfully produced recombinant human oviductin (rHuOVGP1), which has been shown to enhance tyrosine phosphorylation of sperm proteins, a biochemical hallmark of capacitation that takes place in the sperm tail. Additionally, the sex hormone progesterone (P4) has been implicated in increasing the influx of calcium ions through the CatSper channel which is similarly located in the sperm tail and is an important aspect of capacitation. Here we performed a study in the hope of gaining a better understanding of the mechanism of sperm capacitation by examining if rHuOVGP1 works synergistically with P4 to regulate tyrosine phosphorylation of sperm proteins during capacitation. Fresh sperm samples were processed and capacitated at different time points in the absence or presence of rHuOVGP1 (50 mg/mL) with or without P4. The results obtained indicate that both rHuOVGP1 and P4 can enhance tyrosine phosphorylation of sperm proteins, however, the best result was obtained when rHuOVGP1 was used in combination with P4. The addition of rHuOVGP1 with P4 to the capacitation medium may improve the fertilization rates of ART procedures.
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