In vitro fertilization of bovine oocytes in a chemically defined, protein-free medium varying the bicarbonate concentration

Effect of bicarbonate and polyvinyl alcohol on in vitro capacitation and fertilization ability of cryopreserved equine spermatozoa

BACKGROUND

Factors contributing to the limited success of in vitro fertilization in horses remain to be studied. In this work, we elucidated the effect of different essential capacitation media components, bicarbonate, and bovine serum albumin or polyvinyl-alcohol, and the incubation microenvironment on sperm parameters associated with capacitation, acrosome reaction, and their ability to activate oocytes via heterologous intracytoplasmic spermatozoa injection in equine cryopreserved spermatozoa.

METHODS

Frozen-thawed spermatozoa underwent incubation at different time intervals in either Tyrode's albumin lactate pyruvate medium (non-capacitating; NC) or Tyrode's albumin lactate pyruvate supplemented with bicarbonate, bicarbonate and polyvinyl-alcohol, bicarbonate and bovine serum albumin, polyvinyl-alcohol and bovine serum albumin alone. Protein kinase A-phosphorylated substrates and tyrosine phosphorylation levels, sperm motility, and acrosome reaction percentages were evaluated. After determining the best condition media (capacitating; CAP), heterologous intracytoplasmic spermatozoa injection on pig oocytes was performed and the phospholipase C zeta sperm localization pattern was evaluated.

RESULTS

Incubation of frozen-thawed equine spermatozoa with bicarbonate and polyvinyl-alcohol in atmospheric air for 45 min induced an increase in protein kinase A-phosphorylated substrates and tyrosine phosphorylation levels compared to NC condition. Sperm incubation in bicarbonate and polyvinyl-alcohol medium showed an increase in total motility and progressive motility with respect to NC (p ≤ 0.05). Interestingly, three parameters associated with sperm hyperactivation were modulated under bicarbonate and polyvinyl-alcohol conditions. The kinematic parameters curvilinear velocity and amplitude of lateral head displacement significantly increased, while straightness significantly diminished (curvilinear velocity: bicarbonate and polyvinyl-alcohol = 120.9 ± 2.9 vs. NC = 76.91 ± 6.9 µm/s) (amplitude of lateral head displacement: bicarbonate and polyvinyl-alcohol = 1.15 ± 0.02 vs. NC = 0.77 ± 0.03 µm) (straightness: bicarbonate and polyvinyl-alcohol = 0.76 ± 0.01 vs. NC = 0.87 ± 0.02) (p ≤ 0.05). Moreover, the spontaneous acrosome reaction significantly increased in spermatozoa incubated in this condition. Finally, bicarbonate and polyvinyl-alcohol medium was established as CAP medium. Although no differences were found in phospholipase C zeta localization pattern in spermatozoa incubated under CAP, equine spermatozoa pre-incubated in CAP condition for 45 min showed higher fertilization rates when injected into matured pig oocytes (NC: 47.6% vs. CAP 76.5%; p ≤ 0.05).

CONCLUSION

These findings underscore the importance of bicarbonate and polyvinyl-alcohol in supporting critical events associated with in vitro sperm capacitation in the horse, resulting in higher oocyte activation percentages following heterologous intracytoplasmic spermatozoa injection. This protocol could have an impact on reproductive efficiency in the equine breeding industry.

Effect of genistein added to bull semen after thawing on pronuclear and sperm quality

The aim of this research was to study the effect of different genistein treatments on bull sperm after thawing on pronuclear formation after in vitro fertilization (IVF) and on different sperm quality variables. Three experiments were performed. In Experiment 1, three treatments (Control, sperm incubation for 1h at 37 °C with or without genistein) and two sperm concentrations during IVF (1 or 3 × 10(6)sperm/mL) were evaluated to study the influence of genistein on pronuclear formation (PNF). Sperm incubation for 1h before IVF reduced PNF regardless of sperm concentration. However, after sperm incubation and with 3 × 10(6)sperm/mL in IVF, the genistein treatment group had greater fertilization rates than the untreated group. In Experiment 2, six treatments plus the control group were performed to study the effect of genistein (presence or not) and incubation conditions (30 min at 37 °C, 1h at 27 °C or at 37 °C) on PNF using 3 × 10(6)sperm/mL for IVF. When incubation time was reduced to 30 min, PNF rate from the genistein treatment group was no different from either the control group or in the group in which incubation occurred for 1h at 27 °C. In Experiment 3, the effect of several genistein treatments (control; genistein treatment for 30 min of incubation at 37 °C; genistein treatment for 1h of incubation at 27 °C) on sperm motility, viability and DNA fragmentation were evaluated. Genistein did not improve sperm motility and, depending on the experimental group or time, it either reduced or had no effect on sperm motility. Genistein treatment did not improve sperm viability after 5h of incubation. However, genistein treatment for 1h at 27 °C decreased sperm DNA fragmentation compared with the control group after 5h of sperm incubation. In conclusion, the treatment of bull sperm with genistein for 1h at 27 °C could decrease sperm DNA fragmentation, although PNF rate after IVF and sperm motility were reduced.

Effects of different concentrations of aflatoxin B on ram epididymal and ejaculatory sperm viability and motility in vitro

The present study was carried to observe the effect of aflatoxin on ovine sperm in vitro. Ram epididymal and ejaculatory sperm cells were added into media containing different concentrations of aflatoxin B1. When ram epididymal sperm were put in different concentrations of aflatoxin, one-hour post incubation in control group, 81.25% of sperm cells were alive of which, 82.88% were motile. Significantly (p < 0.05) higher than medium with 31.25 ppb and higher concentration. The lowest motility (15.93%) was observed in 62.5 ppb aflatoxin. Sperm viability did not significantly changed after 2nd and 3rd h incubation but significantly decreased in 4th and 5th h post incubation. However, motility was not altered in the 2nd, 3rd, 4th and 5th h post incubation. In ejaculatory sperm, one hour post-incubation, in control group, 83.24% of sperm were alive of which 93.98% were motile, significantly (p < 0.05) higher than motility in medium with 7.81 ppb and higher concentrations of aflatoxin but not different with 1.96 ppb aflatoxin. In 62.5 ppb aflatoxin, the lowest motility was observed (18.9%). Sperm motility patterns for both epididymal and ejaculatory sperm cells were different after incubation in different concentrations of aflatoxin. The results of the present experiment showed that aflatoxin could decrease sperm motility obtained from ejaculation or epididymis.

Heparin and dermatan sulphate induced capacitation of frozen-thawed bull spermatozoa measured by merocyanine-540

Glycosaminoglycans (GAGs) are present in the oviduct in which the major part of sperm capacitation occurs. In this study we have tested how capacitation of frozen-thawed bull spermatozoa is effected by exposure to different GAGs detectable or possibly present in oviductal fluid; i.e. heparin, hyaluronan, heparan sulphate, dermatan sulphate and chondroitin sulphate. Following exposure of different duration, the spermatozoa were stained with either Chlortetracycline (CTC) or merocyanine-540 and evaluated with epifluorescent light microscopy or flow cytometry, respectively. Heparin elicited a significant increase in the number of alive, capacitated spermatozoa, either expressed as higher merocyanine-540 fluorescence (p < 0.0001) or as B-pattern (p = 0.0021) in the CTC assay, during 4 h of incubation. When comparing the different GAG treatments one by one to the negative control in the flow cytometric study, only heparin and dermatan sulphate were significant (p < 0.0001) higher than the control at 0–30 min of incubation. Duration of incubation did not affect the proportion of capacitated spermatozoa when measured as merocyanine-540 fluorescence or CTC B-pattern, but the length of the incubation did affect the number of dead (Yo-PRO 1 positive) spermatozoa (p < 0.0001). Exposure to zona pellucida proteins significantly increased the proportion of acrosome reacted spermatozoa (p = 0.016). Both heparin and dermatan sulphate induce capacitation of frozen-thawed bull spermatozoa in vitro.

In vitrocapacitation of bull spermatozoa by oviductal fluid and its components

Sperm capacitation is crucial for fertilization. However, debate continues on exactly how, where and when capacitation is elicited in the bovine female genital tract. In this study we used merocyanine-540 and the chlortetracycline (CTC) assay to test how capacitation of bull spermatozoa is affectedin vitroby exposure to oviductal fluid (ODF) collectedin vivo, various glycosaminoglycans (GAGs) or bicarbonate. Following different durations of exposure, spermatozoa were stained with CTC or merocyanine-540, and evaluated with epifluorescent light microscopy or flow cytometry, respectively. Incubation time did not significantly affect capacitation. Exposure (30–120 min) to ODF capacitated (p< 0.05) bull spermatozoa as measured by either merocyanine-540 or CTC. Hyaluronan was the only GAG that induced a significant increase in B-pattern spermatozoa (capacitated;p= 0.012) compared with controls. Dermatan sulphate also induced capacitation (merocyanine-540 high fluorescence;p= 0.035). Exposure to bicarbonate-enriched media also yielded an increase in merocyanine-540 high fluorescence (p< 0.0001). When bicarbonate was added to the other treatments (ODF or GAGs) an equal increase in merocyanine-540 high fluorescence was noted (p< 0.0001), compared with before addition of bicarbonate and independent of the treatment before exposure. There was no significant difference in the number of B-pattern spermatozoa when bicarbonate was added, but an significant increase in spermatozoa with an acrosome-reacted (AR)-pattern (p< 0.0001) was observed. Exposure of spermatozoa to solubilized zonae pellucidae significantly increased the AR-pattern spermatozoa (p= 0.016). In conclusion, ODF was more potent in inducing capacitation of bull spermatozoa than the individual GAGs. Our results also indicate that bicarbonate is an effector of bull sperm capacitation.

Prolonging bovine sperm-oocyte incubation in modified medium 199 improves embryo development rate and the viability of vitrified blastocysts

This study was conducted to compare the efficacy of four in vitro fertilization (IVF) media: Bracket and Oliphant's medium (BO), modified medium 199 (IVF-M199), modified Tyrode's medium (MTM), and modified KSOM (m-KSOM) on fertilization efficiency and blastocyst formation rate. In addition, we wanted to investigate the benefit of prolonging the IVF period (from 6 to 18 h) using the two most effective IVF media determined in our initial experiment; subsequently, blastocyst viability was assessed following vitrification. A higher incidence of polyspermic fertilization was observed in the MTM (6%) and in BO, in both the 6 and 18 h (7% and 11%, respectively) groups, than in the m-KSOM (1%) or in the IVF-M199 6 or 18 h (1 and 3%, respectively) groups. Cleavage rates were similar in BO, IVF-M199, and MTM 48 h post-fertilization; however, the lowest cleavage rate was observed for m-KSOM. A greater proportion of zygotes developed into 8-cell embryos in IVF-M199 than in other IVF media. Subsequently, a greater proportion of blastocyst formation and hatching was achieved in IVF-M199 (40% and 79%, respectively) or BO (35% and 74%, respectively) than in m-KSOM (18% and 58%, respectively) or MTM (22% and 66%, respectively). Prolonging IVF to 18 h did not alter cleavage rates; however, the highest rate of overall blastocyst formation was achieved in the IVF-M199 18 h (49%), rather than in the BO 18 h (20%) group. Vitrified/thawed blastocysts from IVF-M199 groups re-expanded and developed better, as compared to the BO 18 h group, and hatching rate and total cell number in IVF-M199 18 h group was comparable to the control groups (non-vitrified). Vitrification reduced survival compared to controls. In conclusion, IVF-M199 was successfully used for IVF, compared favorably to BO medium, and offered the advantage of an extended IVF period for up to 18 h that requires only one-half a dose of semen, and resulted in better quality blastocysts that endured vitrification with a hatching rate comparable to that of control groups.

Effect of capacitation of stallion sperm with polyvinylalcohol or bovine serum albumin on penetration of bovine zona-free or partially zona-removed equine oocytes

Experiments were conducted to study effects of macromolecules on stallion sperm capacitation and fertilization as determined by penetration of bovine zona-free and equine partially zona-removed oocytes. Stallion sperm were capacitated in TYH medium (modified Krebs-Ringer bicarbonate) supplemented with either 1 mg/mL of polyvinylalcohol (PVA) or 4 mg/mL of BSA. Capacitation was induced with 8 bromoadenosine cyclic monophosphate (8BrcAMP; 0.5 mM) alone or in combination with 0.1 microM of ionomycin. Intraspecies gametes were co-incubated in TYH/PVA or TYH/BSA for 18 to 20 h. For zona-free bovine oocytes, penetration rate (35%) with the combination of 8BrcAMP and ionomycin in PVA-containing medium was higher (P < 0.05) than any treatment in BSA-containing medium (5 to 6%). A similar study was conducted using equine oocytes with partially removed zonae. Sperm capacitated and used for in vitro fertilization (IVF) in PVA-containing medium had higher penetration rates (P < 0.01) than sperm in BSA-containing medium (54 vs. 11%). The effect of equine preovulatory follicular fluid on bovine oocyte penetration was assessed. Bovine oocytes were matured in tissue culture medium-199 with 0, 20, 50, or 100% equine preovulatory follicular fluid, and 1 IU/mL of equine chorionic gonadotropin. Stallion sperm were treated with 8BrcAMP + ionomycin in PVA- or BSA-containing media. The penetration rates of bovine zona-free oocytes by stallion sperm were again higher with PVA (47%) than BSA (18%; P < 0.01). Penetration rates of oocytes matured in 100% follicular fluid were higher (P < 0.05) than for oocytes matured with 0% follicular fluid. The effects of equine follicular fluid and PVA/BSA during sperm capacitation on standard bovine IVF were examined. Culture of bovine oocytes with equine follicular fluid did not affect oocyte maturation or penetration rates after IVF. Bovine sperm capacitated with heparin in PVA-containing medium yielded lower (P < 0.05) fertilization rates than those capacitated in BSA-containing medium when incubated with both zona-intact and zona-free bovine oocytes. In summary, PVA was superior to BSA for ionophore-induced capacitation of equine sperm for penetration of zona-free bovine oocytes or partially zona-removed equine oocytes, but not for standard bovine IVF with bovine sperm. Zona-free bovine oocytes may be useful for assaying in vitro capacitation and fertilization of stallion sperm.

How does polyspermy happen in mammalian oocytes?

Polyspermy is one of the most commonly observed abnormal types of fertilization in mammalian oocytes. In vitro fertilization (IVF) provides approaches to study the mechanisms by which oocytes block polyspermic fertilization. Accumulated data indicate that oocyte, sperm and insemination conditions are all related to the occurrence of polyspermic fertilization. A high proportion of immature and aged oocytes showed polyspermy as compared with mature oocytes. Preincubation of oocytes and/or sperm with oviductal epithelial cells or collected oviductal fluid before IVF reduces polyspermic penetration. Recently, it was found that an abnormal zona pellucida is one of main causes of polyspermy in human eggs. A high proportion of polyspermy has resulted from the use of a high concentration of capacitated spermatozoa at the site of fertilization, irrespective of in the in vivo or in vitro environment. Oviductal secretions or oviductal epithelial cells themselves can regulate the number of spermatozoa reaching or binding to the zona pellucida thus reducing multiple sperm penetration. Suboptimal in vitro conditions, such as supplementations in IVF media, pH, and temperature during IVF, also induce polyspermic fertilization in some mammals. Species-specific differences are present regarding the relationship between insemination conditions and polyspermy.

Effect of medium milieu on sperm penetration and pronuclear formation of bovine oocytes matured in vitro

The purpose of the present study was to investigate the optimal concentration of osmolarity, calcium and bicarbonate for sperm penetration and formation of pronuclei (PN), and to investigate the time required for capacitation, penetration across the zona pellucida and formation of PN in bovine cumulus-free oocytes matured in vitro. Bovine follicular oocytes collected at slaughter were matured and fertilized in vitro. Bovine sperm penetrated the zona pellucida in medium containing 240 to 440 mOsm, whereas PN formation was observed in a narrow range of osmolarities, from 280 to 360 mOsm. Maximal penetration by spermatozoa and PN formation was obtained in the medium with 2.5 mM calcium. High rates of spermatozoa penetration were observed in the medium with 37 to 49 mM NaHCO3. However, PN were formed regardless of the concentration of NaHCO3. The times required for sperm capacitation and penetration through the zona pellucida were 260 and 50 min, respectively. The first development of PN was recorded at 120 min after sperm penetration. Therefore, our study suggests that fertilization ability of spermatozoa in vitro appears to be more stable in high concentrations of NaCI. Oocytes are more sensitive to osmotic stress than spermatozoa. Calcium is required for both sperm penetration and PN formation in cumulus-free oocytes, but bicarbonate may be needed mainly for the penetration of spermatozoa.

D-penicillamine and granulosa cells can effectively extend the fertile life span of bovine frozen-thawed spermatozoa in vitro: effect on fertilization and polyspermy

The effect of D-penicillamine on the fertile life span of frozen-thawed bull spermatozoa was studied in Experiment 1. After thawing, the washed spermatozoa were incubated for 8 h in fertilization medium with 1 mg/mL polyvinyl alcohol (PVA) and 0.5 mg/mL D-penicillamine. The addition of cumulus-free oocytes together with 10% of bovine serum (BOS) + 4 IU/mL heparin to the 8-h incubated spermatozoa resulted in high fertilization and polyspermy rates (97/103, 94.2% and 49/97, 50.5%, respectively). When BOS was substituted with 3 mg/mL of BSA, the fertilization and polyspermy rates decreased to 33/91 (36.3%) and 3/33 (9.1%), respectively. The total absence of fertilization was observed after substitution of proteins with PVA. The 8-h sperm incubation in fertilization medium without D-penicillamine and following fertilization in medium + different capacitation supplements resulted in the total absence of or a very low fertilization rate. In Experiment 2, the first set of cumulus-oocyte complexes (COC) and cumulus-free oocytes were fertilized for 8 h with nonincubated spermatozoa. The second set of COC and cumulus-free oocytes were fertilized in the same wells with spermatozoa after removal of the first set. The fertilization rate for the first set of COC and cumulus-free oocytes was 65/67 (97%) and 73/73 (100%), respectively, with 21/65 (32.3%) and 32/73 (43.8%) polyspermy, respectively. In the second set, the high penetration rate (67/73, 91.8%) was observed only for COC, while that for cumulus-free oocytes (19/76, 25%) was significantly lower (P < 0.01). In Experiment 3, the fertilization rate of COC in medium + PVA + 10 or 100 IU/mL heparin was 69/92 (75%) and 52/74 (70.2%), respectively, with no polyspermy. In medium + BSA + 10 or 100 IU/mL heparin, the fertilization rate of COC was 64/72 (88.9%) and 70/79 (88.6%), respectively, with polyspermy at 2/64 (3.1%) and 7/70 (10%), respectively. In medium + BOS + 10 or 100 IU/mL heparin, the fertilization rate was 79/82 (96.3%) and 79/80 (98.7%), respectively, with a significantly (P < 0.05) higher polyspermy rate (34/79, 43% and 30/79, 38%, respectively). The vitality and capacitation changes of frozen-thawed and 8-h incubated spermatozoa were assessed by Hoechst and chlortetracycline (CTC) staining.

The effect of macromolecular supplementation on the surface tension of TCM-199 and the utilization of growth factors by bovine oocytes and embryos in culture

The objectives of this study were to determine the surface tension of bovine follicular fluid (BFF) and TCM-199, and the effects of the synthetic surfactant, Twin-80, or FCS, in TCM-199 on surface tension measurements and subsequent effects on bovine oocyte and embryo development. The surface tension of BFF was determined to be approximately 45.5 mN m(-1) at 25 degrees C and approximately 42.7 mN m(-1) at 39 degrees C, which was comparable to the surface tension of TCM-199 containing Twin-80 (45.7 and 43.2 mN m(-1), respectively). There was no difference in surface tension measurements of BFF from follicles 2-7 mm or 8-15 mm in diameter. Both Millipore water and phosphate buffered saline (PBS) had a surface tension measurement of 69.5 mN m(-1) at 39 degrees C. Although the presence of Twin-80 in TCM-199 resulted in a reduction in surface tension measurement as compared with unsupplemented TCM-199, there was no effect on the number of oocytes reaching metaphase II. However, the addition of epidermal growth factor (EGF) to TCM-199 containing Twin-80 did result in increased maturation rates of oocytes in vitro. There was no effect of insulin, transferrin, and selenium (ITS), or EGF on surface tension measurement of TCM-199, but significantly more zygotes cleaved and developed to morulae/blastocysts in TCM-199 containing both Twin-80 and growth factors. The addition of 20 microg EGF ml(-1) to TCM-199 containing Twin-80 was as efficacious in supporting bovine embryos in culture as was the addition of 5% or 10% fetal calf serum. This study demonstrates that surface-active components in culture media positively affect bovine oocyte maturation and embryo development in culture. Data also suggest that non-ionic surfactants, such as Twin-80 in TCM-199, may successfully replace the surface-active properties but not the embryotrophic properties of serum in embryo maturation/culture media. Although commercial TCM-199 (containing Twin-80) did not require the addition of other surface-active compounds to lower surface tension, it did benefit from the addition of growth promoting factors, which were also provided by serum.

High bovine blastocyst development in a static in vitro production system using SOFaa medium supplemented with sodium citrate and myo-inositol with or without serum-proteins

We describe a bovine embryo culture system that supports repeatable high development in the presence of serum or BSA as well as under defined conditions in the absence of those components. In the first experiment, embryo development in SOF with amino acids (SOFaa), sodium citrate (SOFaac) and myo-inositol (SOFaaci) and with BSA or polyvinyl alcohol (PVA) was compared with that in a M199 granulosa cell co-culture (M199 co-culture). Subsequently, development and cell numbers of blastocysts cultured under defined conditions in SOFaaci with PVA (SOFaaci-PVA), or under undefined conditions in SOFaaci with 5% cow serum (SOFaaci-CS) or M199 co-culture were compared. The repeatability of culture results in SOFaaci-CS was checked by weekly replicates (n = 30) spread over 11 months. The viability of embryos developed in SOFaaci-PVA was estimated by transfer of morphologically good blastocysts (n = 10) to synchronized recipients. In the second experiment, the effect of omitting CS or BSA from IVM and IVM-IVF on subsequent embryo development in SOFaaci-PVA or in SOFaaci-CS was investigated. Blastocyst development in SOFaa-PVA, SOFaac-PVA, SOFaa-BSA and M199 was 16 +/- 3b, 23 +/- 2ab, 30 +/- 8a and 36 +/- 7a%, respectively (Pab < 0.05). Additional inclusion of myoinositol resulted in 42 +/- 1a% blastocysts in SOFaaci-PVA vs 19 +/- 3b% in SOFaac-PVA, 47 +/- 7a% in SOFaac-BSA, and 36 +/- 7a% in M199 co-culture, respectively (Pab < 0.01). In 30 replicates, the average cleavage and blastocyst rates of oocytes in SOFaaci-CS were 87 +/- 4 and 49 +/- 5%, respectively. Five normal calves were produced after transfer of 10 blastocysts developed in defined culture medium (i.e., SOFaaci-PVA). Defined IVM or IVM-IVF (i.e., in absence of CS and BSA) reduced cleavage rates (83 +/- 3 and 55 +/- 3% vs 90 +/- 1% in presence of CS; P < 0.01). Subsequent embryo development in SOFaaci-CS was not affected in either of these defined conditions. However, cleavage and blastocyst rates under completely defined IVP conditions were 54 +/- 7 and 19 +/- 4%, respectively. It was concluded that under defined culture conditions, addition of citrate and myo-inositol improved blastocyst development to rates comparable to those obtained with serum, BSA or co-culture and that the quality of blastocysts was not affected by the absence of serum or BSA. However, serum was essential during IVM/IVF for normal fertilization and subsequent high blastocyst development.

Cyclodextrin removes cholesterol from mouse sperm and induces capacitation in a protein-free medium

Cyclodextrin, which stimulates cholesterol efflux from cells, was examined for its ability to induce capacitation of mouse spermatozoa. A chemically defined, protein-free medium was used for in vitro fertilization of cumulus-free mouse eggs. Fertilization did not occur in modified Krebs-Ringer bicarbonate medium (TYH) supplemented with 1 mg/ml polyvinylalcohol instead of BSA. However, fertilization was observed when spermatozoa were preincubated with methyl-beta-cyclodextrin (MBCD); fertilization rates increased dose-dependently from 0.25 to 0.75 mM MBCD. The fertilization rate decreased when 0.75 mM MBCD was added to both preincubation and fertilization media versus only the preincubation medium (21% vs. 53%); in sharp contrast, fertilization increased when 4 mg/ml BSA was present in both of the media versus the preincubation medium only (66% vs. 25%). At 0.75 mM, 2-hydroxy-beta-cyclodextrin had a lower ability to capacitate spermatozoa in vitro than MBCD (14% vs. 41%). Eggs fertilized by spermatozoa treated with MBCD (0.75 mM) developed to blastocysts (45%, 36 of 80) when cultured in KSOM. When 160 fertilized eggs were transferred to ICR recipients, 62 live offspring were born. After incubation of mouse spermatozoa for 90 min in 0.75 mM MBCD in TYH medium, the cholesterol content of the spermatozoa was significantly (p < 0.01) lower than that of the control (2.27 +/- 0.09 vs. 4.13 +/- 0.09 nmol unesterified cholesterol/10(7) sperm; mean +/- SEM, n = 5). The proportion of capacitated (B pattern) spermatozoa determined by chlortetracycline fluorescence was higher with MBCD treatment for 90 min than for the control (45% vs. 15%; p < 0.01). The proportion of acrosome-reacted (AR pattern) spermatozoa was not different between MBCD treatment and the control. Therefore, MBCD increased capacitation rather than the acrosome reaction of spermatozoa.

Effects of caffeine and/or heparin in a chemically defined medium with or without glucose on in vitro penetration of bovine oocytes and their subsequent development

Bovine cumulus-enclosed oocytes were matured in culture for 22 to 24 h, freed from cumulus cells and inseminated with frozen-thawed spermatozoa in a chemically defined medium containing 1 mg polyvinylalcohol/ml with or without 5 mM caffeine and/or 10 micrograms heparin/ml and 13.9 mM glucose. Penetration of oocytes was observed only in the medium containing caffeine and/or heparin. Regardless of the presence of glucose, similar proportions of oocytes were penetrated in the medium containing heparin with (73 and 83%) or without (36 and 41%) caffeine. However, when the medium was supplemented with caffeine only, a higher penetration rate was observed in the presence (41%) than in the absence (27%) of glucose. When oocytes inseminated in medium containing caffeine and heparin with or without glucose were cultured in a chemically defined, protein-free medium, 72 and 90% and 9 and 21% of inseminated oocytes developed to the > or = 2-cell and blastocyst stages 48 and 192 h post insemination, respectively. These results, obtained using chemically defined conditions, indicate that glucose is required for stimulating fertilization in vitro of bovine oocytes and that synergistic action of caffeine and heparin appears independently of the reversing activity of caffeine on the inhibition of heparin-induced sperm capacitation by glucose.

In vitro maturation, fertilization and culture to blastocysts of bovine oocytes in protein-free media

This study examined the role of protein supplementation at the various steps of the in vitro production of bovine embryos derived from two different morphological categories of COC. The basic medium was TCM 199 and was supplemented with hormones during maturation in vitro and either estrous cow serum (ECS), bovine serum albumin (BSA) at various concentrations or polyvinyl-alcohol (PVA). Fertilization in vitro was carried out using frozen-thawed semen or one bull in Fert-talp containing heparin, hypotaurin and epinephrine and either 6 mg/ml BSA or 1 mg/ml PVA. In vitro culture up to the blastocyst stage was performed in TCM 199 supplemented with either ECS, BSA or PVA. The first experiment investigated the influence of different medium-supplements (ECS, BSA or PVA) on nuclear maturation and revealed no significant differences among treatment groups nor between categories of COC (63.9% to 74.9% and 48.9% to 77.0%, respectively). The time course of in vitro fertilization was elucidated in Experiment 2 in medium supplemented with either protein or PVA during maturation and fertilization. Penetration was not affected (70.9% to 79.3% penetration 12 h after onset of oocyte-sperm-co-incubation), but formation of pronuclei was decreased (P < 0.05) 12 and 19 h after onset of oocyte-sperm-co-incubation and was retarded in medium supplemented with PVA (12 h: 63.8 vs 21.4 %; 19 h: 57.5 vs 20.8 %, respectively) while cleavage was not affected. In Experiment 3, six treatment groups were formed in which the two different morphological categories of cumulus-oocyte-complexes (COC) were incubated in basic medium supplemented with 1) ECS during maturation and embryo culture and BSA during fertilization; 2) PVA during maturation and embryo culture, fertilization medium with PVA; 3) PVA during maturation and embryo culture, fertilization medium with BSA; 4) BSA (1 mg/ml) during maturation, fertilization and embryo culture; 5) BSA (6 mg/ml) during maturation, fertilization and embryo culture; and 6) BSA (10 mg/ml) during maturation, fertilization and embryo culture. The rates of cleavage and the development to morulae or blastocysts did not differ (P > 0.05) among treatment groups and between both categories of COC and were showing a high degree of variability (cleavage 54.0% to 65.1% and 41.3% to 55.7%, respectively; morulae 25.3% to 53.0% and 26.0% to 51.2%, respectively; blastocysts 5.4% to 24.7% and 0.6% to 20.3%, respectively). Parthenogenetic activation only rarely occurred in medium containing PVA throughout all steps of in vitro production of bovine embryos (Experiment 4) and led to early cleavage stages (8%), but no development to morula- or blastocyst-stages was observed. It is concluded that 1) formation of pronuclei was retarded in medium lacking protein-supplementation, indicating that BSA is required for regular fertilization in vitro and 2) under our experimental conditions, protein-supplementation is not necessary for maturation and development up to the blastocyst stage in vitro.