In vitro penetration of zona pellucida of salt-stored bovine oocytes before and after maturation by frozen-thawed spermatozoa

Effect of Mare Age on Transcript Abundance of Connexins-37 and -43, Zona Pellucida Proteins, and Sperm Binding

Zona pellucida (ZP) proteins are important for fertilization and sperm binding and are closely associated with cumulus cells. Communication between cumulus and oocytes is facilitated by intracellular membrane channels composed of connexins. The extent aging impacts potential differences in fertilization and reductions in fertility is not well understood. This study characterized age-related differences in transcript abundance of ZP proteins and connexins in cells from ovarian follicles. Additionally, differences in sperm binding to oocytes from old and young mares was evaluated. For experiment 1, oocytes, corona radiata, cumulus, and granulosa cells were collected from mares classified as young (4-12 years) or old (> 20 years). Transcript abundance was evaluated for connexins -37 (GJA4) and -43 (GJA1); zona pellucida glycoproteins 1, 2, 3, and 4 (ZP1, ZP2, ZP3, ZP4); Tubulin (TUBA1A), and equine chorionic gonadotropin β. For experiment 2, oocytes that failed to cleave following intracytoplasmic sperm injection (ICSI) were stored in salt solution for up to 4 years and used for sperm binding assays. Transcript abundance for GJA1 was decreased in oocytes, corona radiata, and granulosa cells while GJA4 was decreased in cumulus cells from old compared to young mares. Additionally, ZP1 tended to be decreased in corona radiata and cumulus cells from old mares. Oocytes from old mares tended to bind less spermatozoa compared young mares. Oocytes that failed to cleave following ICSI can be used for sperm binding studies for up to 2 years without losses in sperm binding. Our findings suggest that maternal age may contribute to changes in cellular communication and the ZP that could impact sperm binding.

Preservation of sperm within the mouse cauda epididymidis in salt or sugars at room temperature

The development of preservation techniques for male gametes at room temperature might allow us to store them in a simple and cost-effective manner. In this study, we studied the use of pure salt or sugar to preserve the whole cauda epididymidis, because it is known that food can be preserved in this way at room temperature for long periods. Mouse epididymides were placed directly in powdered salt (NaCl) or sugars (glucose or raffinose) for 1 day to 1 year at room temperature. Spermatozoa were recovered from the preserved organs after being rehydrated with medium and then isolated sperm heads were microinjected into fresh oocytes. Importantly, the oocyte activation capacity of spermatozoa was maintained after epididymal storage in NaCl for 1 year, whereas most untreated spermatozoa failed to activate oocytes within 1 month of storage. Pronuclear morphology, the rate of extrusion of a second polar body and the methylation status of histone H3 lysine 9 (H3K9me3) in those zygotes were similar to those of zygotes fertilized with fresh spermatozoa. However, the developmental ability of the zygotes decreased within 1 day of sperm storage. This effect led to nuclear fragmentation at the 2-cell embryo stage, irrespective of the storage method used. Thus, although the preserved sperm failed to allow embryo development, their oocyte activation factors were maintained by salt storage of the epididymis for up to 1 year at room temperature.

Evaluation of the function of fresh and frozen - thawed sex-sorted and non-sorted stallion spermatozoa using a heterologous oocyte binding assay

The aim of the present study was to evaluate the potential oocyte binding ability and functional integrity of fresh or frozen–thawed, sex-sorted or non-sorted stallion spermatozoa. In the absence of effective IVF procedures in the horse, a heterologous sperm-binding assay was used as an indicator of fertilising capacity to assess differences in the ability of stallion spermatozoa to bind to bovine oocytes. The functional integrity of four treatment groups was assessed: (1) fresh non-sorted spermatozoa; (2) fresh sex-sorted spermatozoa; (3) frozen–thawed non-sorted spermatozoa; and (4) frozen–thawed sex-sorted spermatozoa. Spermatozoa found in association with the zona pellucida of the bovine oocytes were deemed ‘attached’ or ‘bound’ depending on their characterisation as either acrosome intact or acrosome reacted, respectively. Significantly less frozen–thawed spermatozoa were found attached to the oocytes compared with fresh spermatozoa. No significant differences were identified between the number of attached sex-sorted and non-sorted frozen–thawed spermatozoa. However, significantly more sex-sorted than non-sorted fresh spermatozoa were found attached to the oocytes after 1 h coincubation, although after 3 h coincubation this difference was no longer apparent. In conclusion, sex-sorted fresh and frozen–thawed stallion spermatozoa are functionally capable of attaching and binding to bovine oocytes in vitro. Furthermore, fresh sex-sorted spermatozoa attach better than non-sorted spermatozoa, suggesting that they have a more advanced capacitation-like status.

Importance of sperm-binding assays for fertility prognosis of porcine spermatozoa

There has been a considerable effort to establish correlations between the outcome of in vitro sperm-binding assays and the fertility achieved by individual males under conditions of commercial AI. During passage through the oviduct, a fertilizing spermatozoon has to bind to and interact with several targets. Generally, it is assumed that these interactions can be mimicked by in vitro binding assays. However, there is little evidence that assays based on zona binding, zona penetration, or IVF: (a) have been adequately validated; (b) provide data with a high degree of correlation to a boar of average fertility; (c) provide accurate predictions as to pregnancy rate and litter size from a given boar when used for commercial AI. This is due partly to the variability in measurements of pregnancy rate and litter size in a commercial setting and partly to the fact that sperm fertility is multifactorial. A recently developed in vitro test is based on the fact that spermatozoa bind in vivo to oviduct epithelium, creating a functional sperm reservoir, and that fertilization-competent spermatozoa are released in a time-dependent manner from these cells. Mating or insemination occurs usually hours before ovulation thus rendering such temporary sperm binding to the epithelial cells, a prerequisite for successful sperm-oocyte interaction. In vitro binding of porcine spermatozoa to explants derived from fresh oviduct epithelium may provide a useful test system to predict fertility, although detailed validation has not been published. The sperm-oviduct-binding assay tests for multifunctional characteristics of the plasma membrane and may be a valuable in vitro test to identify subfertile boars. We believe that boar subfertility might be indicated in vitro by reduced capacity of his spermatozoa to bind to oviductal cells and that this may provide information as to whether an adequate sperm reservoir will presumably be established in vivo from the sperm population that successfully has passed the barriers of the utero-tubal junction.

Gonadotropin exposure, salt storage and storage duration affect penetration of domestic cat oocytes by homologous spermatozoa

Salt-stored domestic cat oocytes are routinely used to study sperm function in domestic and nondomestic felids. Our objectives were to assess the effects of in vitro maturation (IVM), salt storage and storage duration on penetration of domestic cat oocytes by homologous spermatozoa. In Experiment 1, domestic cat spermatozoa were coincubated with fresh immature oocytes, salt-stored (2-3 weeks) immature oocytes, or salt-stored (2-3 weeks) IVM oocytes matured in Minimum Essential Medium containing 0.1IU FSH and 0.1IU LH/ml (IVM1) or 0.5IU FSH and 2.2IULH/ml (IVM2). In Experiment 2, all oocytes were matured (IVM2) and inseminated fresh or after salt storage for 2-3 weeks, 2-3 months or 9 months. In Experiment 1, penetration of the outer zona pellucida (OZP) was greater (P<0.05) in salt-stored IVM2 oocytes than in salt-stored immature oocytes, whereas penetration of salt-stored IVM1 oocytes was intermediate (P>0.05). In Experiment 2, penetration of the OZP and inner zona pellucida (IZP) was higher (P<0.05) in fresh IVM2 oocytes than in salt-stored oocytes, and a higher (P<0.05) proportion of oocytes had IZP sperm after 2-3 weeks of storage than after 2-3 months. Penetration of the perivitelline space was higher (P<0.05) in fresh IVM2 oocytes than in oocytes stored for 2-3 weeks or 2-3 months. These results suggest that oocyte penetration is improved by IVM, but is impaired by exposure to salt-storage solution and prolonged storage duration.

The effects of oocyte storage and cumulus cell presence on canine zona penetration by domestic dog spermatozoa

Zona penetration assays (ZPAs) have been developed in numerous species to evaluate sperm fertilizing potential. Preservation methods to stockpile oocytes would be beneficial because of the difficulty in obtaining sufficient numbers of fresh oocytes. Using a canine ZPA, the objectives of this study were to evaluate: (1) two methods of storing canine oocytes (salt storage and intrafollicular cooling) and (2) the effects of cumulus cells on oocyte penetration. In experiment 1. oocytes from fresh ovaries were assigned at random to 3 categories: fresh control (FRE), salt storage in solution 1 (1.5 M MgCl2.6H2O; SS1) and salt storage in solution 2 (0.5 M (NH4)2SO4, 0.75 M MgCl2.6H2O, 0.2 mM ZnCl2; SS2). Each category was subdivided into two treatments: cumulus cells intact (intact) and cumulus cells removed (denuded), resulting in a total of six treatments with n > 15 oocytes per treatment for each ejaculate. Fresh (FRE) intact oocytes demonstrated greater sperm-oocyte interaction than other treatments, including FRE denuded oocytes (11.7 +/- 0.6 versus <4.1 +/- 0.5 sperm-oocyte and 94.9 versus <55.6% penetration; P < 0.01). Poor sperm-oocyte interaction was demonstrated with all salt-stored oocytes (< or = 1.6 +/- 0.2 sperm-oocyte and < 51% penetration), but was further attenuated in the absence of cumulus cells. In experiment 2, oocytes obtained from fresh (FRESH) or cooled (24 h COOL, 48 h COOL) ovaries were used with cumulus cells intact for a total of three treatments with n > 15 oocytes per treatment for each ejaculate. No significant difference was observed in sperm interaction between oocytes from fresh, 24 and 48 h COOL ovaries ( 12.3 +/- 0.5 to 13.1 +/- 0.4 sperm-oocyte and 92.2-97.7% penetration; P > 0.01). These results indicate that salt storage may cause damage to canine oocytes, subsequently impairing sperm penetration, whereas short-term intrafollicular cooling does not affect the oocyte's penetrability. Furthermore, greater sperm interaction in oocytes with an intact cumulus suggests a possible role for cumulus cells in canine gamete interaction.

Can we use in vitro fertilization tests to predict semen fertility?

This presentation deals with assays based on in vitro fertilization (IVF) and related techniques such as zona pellucida (ZP) binding assays and oocyte penetration tests. These types of assays have been developed for several species of domestic animals. A description of the assays and how they have been performed in domestic animals, as well as data on the correlation between the results of assays and actual in vivo fertility are presented. Used either as single tests or in combination with other tests, this type of assay can provide valuable information about a semen donor, an insemination dose or a method of semen preservation.

Estrous sheep serum as a potent agent for ovine IVF: Effect on cholesterol efflux from spermatozoa and the acrosome reaction

The aim of the present study was to evaluate the effect of heat-inactivated estrous sheep serum (ESS) on sheep IVF. When the capacitation and the fertilization media contained 20% ESS, a fertilization rate of 85% was achieved. The beneficial effect of ESS on sheep IVF was further demonstrated since the fertilization rate was null when ESS was omitted during sperm capacitation and fertilization. Estrous sheep serum supported both sperm capacitation and fertilization as shown by the results of experiments in which it was omitted during one of these steps: sperm capacitation in serum-free medium resulted in delayed sperm-oocyte penetration, while fertilization in serum-free medium significantly decreased the percentage of fertilized oocytes. To investigate the influence of serum on sperm ability to undergo the acrosome reaction, salt-stored follicular sheep oocytes were inseminated, and the acrosomal status of spermatozoa attached to zonae was examined by electron microscopy after a 4-h period of coincubation. Quantitative analysis on thin sections demonstrated that fewer acrosome-reacted spermatozoa were observed when the capacitation and insemination steps were carried out in DM-H medium without serum than in DM-H-SS supplemented with 20% ESS (0.08, [0; 0.34], (median, range)/100 microm zona vs 1.32, [0.90; 2.28]/100 microm zona; P<0.01). Since a higher number of spermatozoa attached to the zona surface in DM-H medium, the proportion of acrosome-reacted spermatozoa was much lower (0.7%, [0%; 2.2%], (median, range) vs 54%, [25%; 100%]; P<0.01) in the absence of serum. These results indicate that in our IVF system the development of the acrosome reaction depended on serum. Sperm cholesterol efflux during in vitro capacitation was measured on [3H] cholesterol labeled spermatozoa resuspended in DM-H or DM-H-SS medium. A time-dependent cholesterol removal was observed in the presence of serum (60+/-5%, mean+/-SD, after 5 h), whereas it was limited to 14+/-3% in DM-H medium; hence addition of serum to the capacitation medium efficiently supports cholesterol efflux, which is thought to be a key-event in the capacitation process.

Penetration by bull spermatozoa into the zona pellucida of dead bovine oocytes recovered from frozen-thawed ovaries

The present study was carried out to determine if the zona pellucida of dead bovine oocytes obtained from ovaries stored at -196 degrees C could be used to assess penetrability of capacitated bull spermatozoa. Follicular oocytes were recovered from bovine ovaries which were frozen slowly in a box containing dry ice, plunged into liquid nitrogen, and thawed at 37 degrees C. The dead oocytes were inseminated with various concentrations of spermatozoa preincubated for 0 to 4 h. Sperm penetration rates of the dead oocytes were significantly altered by sperm concentration and preincubation time. Dead and living oocytes matured in vitro (control) gave similar patterns of penetrability based on sperm preincubation time. When sperm concentration was increased, the rate of multiple sperm penetration into the dead oocytes also increased significantly, but the rate of penetration into living oocytes did not alter significantly. All dead oocytes from ovaries stored at -196 degrees C for 1 d to 3 mo were penetrated at similar rates by spermatozoa preincubated for 1-h. Thus, we conclude that dead follicular oocytes recovered from frozen ovaries are useful for the assessment of sperm capacitation and/or the acrosome reaction in cattle.

Moderate heat treatment increases the penetrability of zonae pellucidae of salt-stored mammalian oocytes by spermatozoa

The zona pellucida of mammalian oocytes stored in highly concentrated solutions of neutral salts is known to retain its biological and biochemical properties. However, the zona may become resistant to sperm penetration as the storage period is increased. In cattle and hamsters, the penetrability of zonae of salt-stored oocytes was restored or increased by treating the oocytes with moderate heat without altering the gross morphology of the zona. Although this technique did not work for salt-stored human ova, this may have been due to the use of so-called inseminated-unfertilised ova which (1) may have been fertilised but failed to activate, or (2) were not fertilised because of functionally defective zonae.