Modifications of surface carbohydrates on bovine spermatozoa mediated by oviductal fluid: a flow cytometric study using lectins

Mannosylated glycoconjugates on the surface of activated sperm in the giant freshwater prawn are crucial for sperm binding with the egg vitelline envelop

The unusual morphology and poorly defined acrosome-like structure in the mature sperm of the giant freshwater prawn Macrobrachium rosenbergii has led to difficulties in identifying the state of sperm activation. Mature distal vas deferens sperm (dVSp) can be activated by the calcium ionophore A23187 to show acrosome reaction-like enzymatic activities that increase their binding and penetration capabilities. However, these short-lived enzymatic activities limit their usefulness as a marker of sperm activation for further qualitative and quantitative analyses, leading to our examining the alterations in the exposure of sperm surface glycoconjugates both as markers of sperm activation and for their role in gamete interaction. Our results showed that after A23187 treatment, there was an increased exposure of mannosylated glycoconjugates on the sperm surface revealed by significant Concanavalin A (Con A) staining. Furthermore, sodium metaperiodate pre-treatment, Con A pre-incubation, or co-incubation with α-mannose monosaccharides all significantly reduced A23187-induced dVSp binding to the egg vitelline envelop, demonstrating the importance of sperm surface mannosylated glycoconjugates in the binding process. These same pre-treatments of sperm also resulted in the inhibition of the binding of soluble vitelline envelop proteins (MrVE) to both the sperm surface and to mannosylated dVSp protein bands. Therefore, the present study demonstrated the importance of the exposure of mannosylated glycoconjugates on the surface of activated dVSp, both as a reliable marker of sperm activation and as a binding factor in the gamete interaction process. Furthermore, these findings allow for a better understanding of the surface glycoconjugate-mediated interaction process between gametes in this species of prawn.

Seminal plasma and cryopreservation alter ram sperm surface carbohydrates and interactions with neutrophils

Spermatozoa deposited vaginally must navigate the physical, chemical and immune barriers of the cervix to reach the site of fertilisation. Characteristics that favour successful cervical transit remain largely unknown beyond the obvious factors of motility and viability. Epididymal and cryopreserved ram spermatozoa demonstrate poor cervical transit, for unknown reasons. We hypothesised that seminal plasma exposure and cryopreservation alter the surface sugars of these sperm populations and, consequently, their interaction with immune cells, both potential factors for successful cervical transit. The carbohydrate profiles of epididymal, ejaculated and frozen–thawed ram spermatozoa were assessed by flow cytometry and western blotting using lectins for galactose, sialic acid, N-acetylglucosamine and mannose. Seminal plasma exposure and cryopreservation caused significant changes to the relative amounts of surface sugars detected by flow cytometry and lectin blotting. Immune cell interaction was characterised using a neutrophil-binding assay. Seminal plasma acted as a robust protective mechanism, limiting binding of spermatozoa, whereas the media used for cryopreservation caused a significant disruption to opsonin-mediated binding. We were unable to demonstrate a link between changes to surface sugars and neutrophil susceptibility. Seminal plasma and cryopreservation clearly alter the sperm glycocalyx, as well as the interaction of spermatozoa with immune cells.

Epididymal α-l-fucosidase and its possible role in remodelling the surface of bull spermatozoa

The mammalian epididymis provides an appropriate environment for sperm maturation. During the epididymal transit, spermatozoa undergo biochemical and morphological changes that lead to the acquisition of the fertilizing capacity. In this study we analysed the fucosylation status of membrane glycoproteins in the spermatozoa obtained from different regions of the bull epididymis. High amounts of fucose were detected on caput spermatozoa (R.F.I. = 1010 ± 20.35), mostly located in the post-acrosome zone. A significant decrease in the fucose levels was detected toward the cauda (R.F.I. = 540.5 ± 49.93) (P < 0.05). This decrease was in line with the increased activity of α-l-fucosidase in the cauda fluid. In sperm from the cauda, the defucosylation occurred in some proteins, whereas others showed higher fucosylation rates. A significant decrease of fucose in the gametes was observed upon incubation of crude cauda fluid with caput spermatozoa (from R.F.I. = 1.45 ± 0.08 to 1.06 ± 0.03) (P < 0.05) indicating that the α-l-fucosidase present in the epididymal fluid is active on spermatozoa. Moreover, this effect was blocked with specific enzyme inhibitors. These results provide direct evidence that the α-l-fucosidase from epididymal fluid participates in the fucose removal from spermatozoa, as a step of sperm maturation in the bull epididymis.

Effects on glycocalyx structures of frozen-thawed bovine sperm induced by flow cytometry and artificial capacitation

Sperm sorting by flow cytometry is a useful technology in the bovine industry, but the conception rates after artificial insemination using sex-sorted sperm are lower than when using the un-sorted sperm. In this study, we have investigated the causes for these low conception rates. We have focused on changes caused by flow cytometry to the glycocalyx, which forms the outermost surface of the sperm membrane. We have also evaluated the effects of capacitation on the glycocalyx since capacitation involves a redistribution of the sperm membrane that is vital for successful fertilization and conception. Lectin histochemistry was used to visualize the structure of the sperm glycocalyx. Lectin-staining sites were examined in non-treated sperm, sex-sorted sperm, and capacitated sperm. We have detected six different staining patterns related to different labeling regions of the sperm. Phaseolus vulgaris–erythroagglutinin (PHA-E) lectin-staining patterns of non-treated sperm were very different from those observed for sex-sorted sperm or capacitated sperm, suggesting that both, sex sorting by flow cytometry and the capacitation process affected the glycocalyx structures in the sperm. In addition, the total tyrosine-phosphorylation level in sex-sorted sperm was significantly higher than that in the non-treated sperm. Therefore, we concluded that the unexpected capacitation of bovine sperm during flow cytometry is associated with changes in the glycocalyx. Since premature capacitation leads to low conception rates, this unexpected capacitation could be a cause of low conception rates after artificial insemination using sex-sorted sperm.

Glycosidases in porcine follicular fluid and their effect on zona pellucida-AWN 1 spermadhesin interaction

Oligosaccharide moieties on the surface of the oocyte belong to the key molecules that direct the course of fertilization and are subjected to changes during oocyte maturation in the follicle. In our study, we focused on the activities of five glycosidases in the fluids from porcine secondary and preovulatory follicles (α-l-fucosidase, α-d-galactosidase, β-d-galactosidase, β-D-N-acetylhexosaminidase, and α-d-mannosidase). All of them were detected active at neutral and acidic pH. However, changes in their activities associated with follicle development were observed only in the case of α-d-mannosidase, which was increased (P < 0.001), and β-d-galactosidase, which was decreased (P < 0.001) at neutral pH, and of α-d-galactosidase and β-N-acetylhexosaminidase, which were decreased (P < 0.0001) at the acidic pH. The comparison of glycosidases from follicular fluid and from blood plasma using red native electrophoresis revealed that most of the glycosidases are present in more than one isoenzyme form; some of them were detected mainly in the follicular fluid. Finally, we tested the effect of glycosidases on the interaction between zona pellucida and AWN 1 spermadhesin (putative sperm receptor of zona pellucida) and demonstrated that the effect of both β-d-galactosidase and to a lesser degree α-d-mannosidase led to a decrease in this interaction. We can hypothesize that these two glycosidases modulate the amount of zona pellucida oligosaccharide moieties and/or their structures for an optimal sperm binding in pigs.

Improved bovine embryo production in an oviduct-on-a-chip system: prevention of poly-spermic fertilization and parthenogenic activation

The oviduct provides the natural micro-environment for gamete interaction, fertilization and early embryo development in mammals, such as the cow. In conventional culture systems, bovine oviduct epithelial cells (BOEC) undergo a rapid loss of essential differentiated cell properties; we aimed to develop a more physiological in vitro oviduct culture system capable of supporting fertilization. U-shaped chambers were produced using stereo-lithography and mounted with polycarbonate membranes, which were used as culture inserts for primary BOECs. Cells were grown to confluence and cultured at an air-liquid interface for 4 to 6 weeks and subsequently either fixed for immune staining, incubated with sperm cells for live-cell imaging, or used in an oocyte penetration study. Confluent BOEC cultures maintained polarization and differentiation status for at least 6 weeks. When sperm and oocytes were introduced into the system, the BOECs supported oocyte penetration in the absence of artificial sperm capacitation factors while also preventing polyspermy and parthenogenic activation, both of which occur in classical in vitro fertilization systems. Moreover, this "oviduct-on-a-chip" allowed live imaging of sperm-oviduct epithelium binding and release. Taken together, we describe for the first time the use of 3D-printing as a step further on bio-mimicking the oviduct, with polarized and differentiated BOECs in a tubular shape that can be perfused or manipulated, which is suitable for live imaging and supports in vitro fertilization.

The activity of three glycosidases (β-Ν-acetyloglucosaminidase, α-mannosidase, and β-galactosidase) in the follicular fluid and in the maturation medium affects bovine oocyte maturation

We studied the role of follicular fluid's (FF) glycosidase (α-mannosidase [α-ΜΑΝ], β-Ν-acetyloglucosaminidase [NAGASE], β-galactosidase [β-GAL]) activity during IVM of bovine oocytes. Oocytes were allocated into two groups according to the follicular size (small follicle [SF]: 2-5 mm, large follicle [LF]: >5-8 mm). In experiment 1, cumulus-oocyte complexes (COCs) quality was evaluated according to morphologic criteria (grades A, B-C, D); oocyte (n = 801) nuclear maturation was assessed after 24 hours of incubation. Bovine embryos were produced in vitro in groups (experiment 2, n = 1503 oocytes) or individually (experiment 3, n = 50 oocytes). More grade-A and -BC COCs were collected from SF and LF groups, respectively (P < 0.05). Maturation rate (experiment 1) and cleavage rate (experiments 2 and 3) were similar in SF and LF groups. Activity of all glycosidases in FF was higher (P < 0.05) in SF group than in LF group, whereas in maturation medium of SF group it was, overall, significantly lower than in that of LF (experiments 2 and 3). In FF of SF group, NAGASE positively associated with grade-A oocytes and negatively with BC oocytes; increased β-GAL was associated with degenerated oocytes. Cleavage rate in LF group, related negatively to NAGASE and positively to α-MAN in maturation medium. These results indicate that during maturation, COCs release NAGASE and consume β-GAL, but differences probably exist between individual and group maturation.

Lectin staining and flow cytometry reveals female-induced sperm acrosome reaction and surface carbohydrate reorganization

All cells are covered by glycans, an individually unique layer of oligo- and polysaccharides that are critical moderators of self-recognition and other cellular-level interactions (e.g. fertilization). The functional similarity between these processes suggests that gamete surface glycans may also have an important, but currently overlooked, role in sexual selection. Here we develop a user-friendly methodological approach designed to facilitate future tests of this possibility. Our proposed method is based on flow cytometric quantification of female-induced sperm acrosome reaction and sperm surface glycan modifications in the Mediterranean mussel Mytilus galloprovincialis. In this species, as with many other taxa, eggs release water-soluble factors that attract conspecific sperm (chemoattraction) and promote potentially measurable changes in sperm behavior and physiology. We demonstrate that flow cytometry is able to identify sperm from other seawater particles as well as accurately measure both acrosome reaction and structural modifications in sperm glycans. This methodological approach can increase our understanding of chemically-moderated gamete-level interactions and individual-specific gamete recognition in Mytilus sp. and other taxa with similar, easily identifiable acrosome structure. Our approach is also likely to be applicable to several other species, since carbohydrate-mediated cellular-level interactions between gametes are universal among externally and internally fertilizing species.

Oviductal secretion and gamete interaction

Experimental evidence from the last 30 years supports the fact that the oviduct is involved in the modulation of the reproductive process in eutherian mammals. Oviductal secretion contains molecules that contribute to regulation of gamete function, gamete interaction, and the early stages of embryo development. The oviductal environment would act as a sperm reservoir, maintaining sperm viability, and modulating the subpopulation of spermatozoa that initiates the capacitation process. It could also contribute to prevent the premature acrosome reaction and to reduce polyspermy. Many studies have reported the beneficial effects of the oviductal environment on fertilization and on the first stages of embryo development. Some oviductal factors have been identified in different mammalian species. The effects of oviductal secretion on the reproductive process could be thought to result from the dynamic combined action (inhibitory or stimulatory) of multiple factors present in the oviductal lumen at different stages of the ovulatory cycle and in the presence of gametes or embryos. It could be hypothesized that the absence of a given molecule would not affect fertility as its action could be compensated by another factor with similar functions. However, any alteration in this balance could affect certain events of the reproductive process and could perhaps impair fertility. Thus, the complexity of the reproductive process warrants a continuous research effort to unveil the mechanisms and factors behind its regulation in the oviductal microenvironment.

Glycosidase determination in bovine oviducal fluid at the follicular and luteal phases of the oestrous cycle

Gamete recognition and binding of spermatozoa to the oviduct are carbohydrate-mediated processes in which several glycosidases are thought to have a role, although this has not been demonstrated unequivocally. Oviducal fluid is the biological milieu in which fertilisation and early embryo development take place, but the enzyme composition of oviducal fluid is largely unknown. The aim of the present study was to determine glycosidase activity and protein content in bovine oviducal fluid (bOF) and the volume of fluid collected per oviduct. Oviducts obtained from a slaughterhouse were classified as either in the follicular or luteal phase on the basis of ovarian luteal morphology. Oviducal fluid was aspirated, centrifuged and the volume determined. Samples were then frozen until assay. Substrates conjugated to 4-methylumbelliferyl were used to screen for the activity of seven glycosidases at pH 7.2. The results indicate that bOF has alpha-l-fucosidase, beta-N-acetyl-glucosaminidase, beta-d-galactosidase, alpha-D-mannosidase and beta-N-acetyl-galactosaminidase activity during both phases of the cycle, with the specific activity of the latter two enzymes being higher during the follicular phase. There was no N-acetyl-neuraminidase or alpha-d-galactosidase activity detected in bOF at either phase of the oestrous cycle at pH 7.2, but activity for both glycosidases was detected at pH 4.4. There were no differences in protein concentration or the volume of bOF collected between the two phases of the cycle. These findings indicate that oviducal fluid exhibits glycosidase activity, with specific variations throughout the oestrous cycle, suggesting that these enzymes play a role in carbohydrate-mediated events.

Determination of glycosidase activity in porcine oviductal fluid at the different phases of the estrous cycle

Sperm-oocyte binding and gamete-oviductal epithelium interactions are carbohydrate-mediated events occurring in the oviductal fluid (OF). Thus, knowledge about the activities of glycosidases (enzymes catalyzing hydrolytic cleavage of terminal sugar residues) in this milieu would help us understand the molecular mechanisms involved in these events. This work was carried out to investigate the glycosidase activity, protein content, and volume of OF collected from gilts and sows. Oviducts were classified into four phases of the estrous cycle (early follicular, late follicular, early luteal, and late luteal) based on the appearance of the ovaries. OF was aspirated, centrifuged, measured for volume, and frozen until assay. Substrates conjugated to 4-methylumbelliferyl were used to screen the activities of seven different glycosidases at physiological pH (7.2). alpha-L-Fucosidase and beta-N-acetyl-glucosaminidase activities increased at the late follicular phase to decrease after ovulation. beta-D-Galactosidase, alpha-D-mannosidase, and beta-N-acetyl-galactosaminidase showed higher activities at the early follicular phase, which decreased after ovulation. N-Acetyl-neuraminidase and alpha-D-galactosidase did not show activity at any phase of estrous cycle neither in sows nor in gilts at pH 7.2, although it did at acidic pH (4.4) in the follicular and luteal phase samples. Total protein also changed during the cycle showing the maximum secretion at the late follicular phase (2118.6+/-200.7 microg/oviduct). The highest volumes of OF were collected from the oviducts at the late follicular phase (50.7+/-1.3 microl/oviduct). These results indicate that OF from sows and gilts shows glycosidase activity varying throughout the estrous cycle suggesting a role of these enzymes in carbohydrate-mediated events.