The effects of an ovine oviductal estrus-associated glycoprotein on early embryo development

Recombinant human OVGP1 increases intracellular calcium and further potentiates the effects of progesterone on human sperm

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.

Supplementary information

The online version contains supplementary material available at 10.1007/s10815-022-02591-0.

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.

Investigation of the oviductal glycoprotein 1 (OVGP1) gene associated with embryo survival and development in the rabbit

An association study was performed in rabbits between early embryo survival and development, and the nonconservative SNP 12944C>G located in exon 11 and the triallellic microsatellite [(GT)(15)T(G)(5), (GT)(14)T(G)(5), and (GT)(11)T(G)(7))] located in the promoter region of the oviductal glycoprotein 1 (OVGP1) gene. We analyzed an F(2) cross of 2 lines of rabbits divergently selected for uterine capacity. A total of 172 and 159 females were slaughtered at 48 and 72 h of gestation, respectively, to determine whether OVGP1 influences ovulation rate, fertilization rate, early embryo survival, and embryonic stage of development. The results of the SNP indicated that all genotypes showed similar early embryo survival and a similar embryonic stage of development at 48 h of gestation. However, at 72 h of gestation, the GG genotype showed greater early embryo survival than the CC genotype (0.56 embryos) and their embryos presented less embryonic development. Analysis of the microsatellite was performed to ascertain the presence or absence of the allele (GT)(14)T(G)(5). At both stages of gestation, the (GT)(14)T(G)(5)/(GT)(14)T(G)(5) genotype showed greater early embryo survival (0.94 and 1.54 embryos at 48 and 72 h of gestation, respectively) and less embryonic development than the homozygous genotypes without the allele (GT)(14)T(G)(5).

In vitro maturation of bitch oocytes from advanced preantral follicles in synthetic oviduct fluid medium: serum is not essential

The ability of oocytes from preantral follicles to mature in vitro was assessed using a synthetic oviduct fluid (SOF) medium. Advanced preantral follicles (approximately 210 microm diameter) were isolated from the ovaries of domestic bitches and assigned to one of four treatment groups: (1) SOF (n = 230); (2) SOF + 3 mg/ml bovine serum albumin (+BSA, n = 220); (3) SOF + 20% fetal bovine serum (+FBS, n = 227); or (4) SOF + 3 mg/ml BSA + 20% FBS (+BSA+FBS, n = 232), then cultured for up to 72 h. A group of control follicles was not cultured (n = 103). The percentages of oocytes reaching metaphase I to metaphase II stages (MI to MII) did not differ between treatments at each culture period. Within treatments, the percentages of oocytes at MI to MII stages did not differ with duration of culture. However, when compared to the control group (0.97%) the percentages of oocytes at MI to MII increased (P < 0.05) in the SOF group after 48 h (10.0%) and 72 h (12.2%) of culture. In the +BSA (10.1%) and +FBS (9.7%) groups, the percentages of oocytes at MI to MII increased (P < 0.05) above control values only after 72 h of culture. The percentage of oocytes at MI to MII did not significantly increase in the +BSA+FBS group (3.9,6.6 and 7.6% at 24,48 and 72 h of culture, respectively) compared to the control group. These results indicate that under the described conditions supplementation of culture medium with BSA or FBS is not essential, and the simple medium SOF can support nuclear maturation of a small proportion of bitch oocytes in vitro.

Production of sheep embryos in vitro and development of progeny following single and twin embryo transfers

An in vitro culture system for producing ovine embryos is described, in which heat inactivated sheep serum was used as a protein source for maturation, fertilization and 7-d culture phases. Ovaries obtained from a commercial abattoir were used as the source of mature ewe (285) and lamb oocytes (356), which were subsequently cultured in this system to yield similar mean cleavage rates of 91 and 92%, respectively, but significantly different (P < 0.025) proportions for blastocysts/cleaved oocytes (46 and 18%). At Days 7 or 8 of culture, embryos from each source were transferred, either singly (ewe-derived) or in pairs (ewe- and lamb-derived), to hormonally synchronized recipient ewes, resulting in the birth of lambs ranging in weight from 2.5 to 8.8 kg for singletons and 2.6 to 8.0 kg for twins. Mean gestation length of 153.4 +/- 0.5 d (range 151 to 160) was slightly longer than the expected norm of about 150 d. The pregnancy rate was significantly higher after the transfer of embryo pairs (64%) than single (39%) embryos, while survival of lambs to weaning was greater for singleton (80%) than for twin lambs (43%). Some factor(s) in the culture media, such as growth factors in the sera, may have a mitogenic effect on embryonic cells, or it may alter the distribution of cells to the trophectoderm and inner cell mass, resulting in enhanced body growth rates.

Influence of ovine oviducal amino acid concentrations and an ovine oestrus-associated glycoprotein on development and viability of bovine embryos

This study examined the effects of incorporating an ovine oviducal oestrus-associated glycoprotein (oEGP) and amino acids, at the concentrations present in the ovine oviduct around the time of oestrus, on in vitro production and subsequent viability of bovine embryos. The first experiment compared the influence of ovine oviducal concentrations of amino acids with MEM and BME amino acids. There was no treatment effect on cleavage rate (74.9% vs. 75.5%), but there was a higher (P < 0.05) blastocyst yield (30.4 vs. 25.2) and a shorter time (P < 0.05) to blastocyst formation (7.16 +/- 0.64 vs. 7.27 +/- 0.56 days) following use of oviducal concentrations of amino acids. Experiment 2 examined the influence of oEGP in combination with each of the amino acid treatments. oEGP had no effect on cleavage or blastocyst yield within amino acid treatments. Day of blastocyst formation significantly influenced nuclei numbers (P < 0.001) with higher numbers being obtained on day 7 than on either day 6 or day 8. There was also a significant (P < 0.01) interaction between day of blastocyst formation and amino acid treatment on blastocyst nuclei numbers. The third experiment studied the effects of the amino acid treatments on embryo viability. There was no effect of amino acid treatment of embryos on pregnancy rates (34.5 vs. 44.4%) following transfer of days 6 and 7 blastocysts to synchronized recipients. oEGP did not influence any of the parameters of bovine embryo development that were measured, suggesting that effects of this protein observed on ovine embryos are species specific. It is concluded that ovine oviducal amino acid concentrations are beneficial to blastocyst development in vitro but do not have any further beneficial effect following transfer of blastocysts to recipients.