Microtubule and microfilament organization in porcine oocytes during maturation in vivo and in vitro was imaged by immunocytochemistry and laser scanning confocal microscopy. At the germinal vesicle stage, microtubules were not detected in the oocyte. After germinal vesicle breakdown, a small microtubule aster was observed near the condensed chromatin. During the prometaphase stage, microtubule asters were found in association with each chromatin mass. The asters then elongated and encompassed the chromatin at the metaphase‐I stage. At anaphase‐I and telophase‐I microtubules were detected in the meiotic spindle. Microtubules were observed only in the second meiotic spindle at the metaphase‐II stage. The meiotic spindle was a symmetric, barrel‐shaped structure containing anastral broad poles, located peripherally and radially oriented. Taxol, a microtubule‐stabilizing agent, did not induce microtubules in oocytes at the germinal vesicle stage. After germinal vesicle breakdown, numerous cytoplasmic foci of microtubules were formed in the entire oocyte when oocytes were incubated in the presence of taxol. Microfilaments were observed as a relatively thick uniform area around the cell cortex and were also found throughout the cytoplasm of oocytes at the germinal vesicle stage. After germinal vesicle breakdown, the microfilaments were concentrated close to the female chromatin. During prometaphase, microfilaments were chromatin moved to the peripheral position. At metaphase‐I, two domains, a thick and a thin microfilament area, existed in the egg cortex. Chromosomes were located in the thick microfilament domain of the cortex. In summary, these results suggest that both micro‐tubules and microfilaments are closely involved with chromosomal dynamics after germinal vesicle breakdown and during meiotic maturation in porcine oocytes. © 1996 Wiley‐Liss, Inc.

Microtubule configurations in porcine oocytes after sperm penetration or after artificial activation by electrical stimulation were imaged by immunocytochemistry and laser scanning confocal microscopy. Soon after sperm penetration, an aster was seen adjacent to the incorporated sperm head. Polyspermic penetrations led to the presence of multiple sperm asters in association with each sperm. The sperm aster enlarged and, at the time of pronuclear apposition, filled the cytoplasm. After male and female gamete union, the microtubule matrix was reduced. At the mitotic metaphase stage, microtubules were detected in the spindle, which was anastral and fusiform. At anaphase, asters assembled at each spindle pole, and at telophase, large asters filled the cytoplasm. Artificial activation by electrical stimulation induced in the cytoplasm a dense network of microtubules, which seem to be involved in proper positioning of the female pronucleus. At mitotic metaphase, microtubules were concentrated around the chromatin. The results of experiments using taxol, a microtubule stabilizing agent, suggest that maternal centrosomal material is present in the mature porcine oocyte as dispersed undetectable material that can form a microtubule network after parthenogenetic activation. However, at fertilization, the paternal centrosome collects centrosomal material to form a sperm aster. These results suggest that the functional centrosome that forms during fertilization is a result of the blending of paternal and maternal centrosomal components.

The effects of organic osmolytes on cytoplasmic maturation of porcine oocytes were examined in maturation medium (modified Whitten's medium) containing various NaCl concentrations. The presence of organic osmolytes, such as taurine and sorbitol, at 6 and 12 mM in maturation medium containing 68.49 or 92.40 mM NaCl increased oocyte glutathione content. Microfilament organization in oocytes was disrupted in maturation medium containing the higher level of NaCl (92.40 mM). However, supplementation with 12 mM sorbitol to the medium reduced the severity of the abnormality. Early embryonic development in vitro to the blastocyst stage was 8.3 +/- 0.9% for oocytes matured in modified Whitten's medium (68.49 mM NaCl) supplemented with 12 mM sorbitol, and 7.9 +/- 0.8% in modified NCSU23 medium (containing 108.73 mM NaCl, 7 mM taurine, 5 mM hypotaurine, and 1 mM glutamine), compared to 4.7 +/- 0.6% in modified Whitten's medium (68.49 mM Na Cl), which did not contain organic osmolytes. These results indicate that the presence of organic osmolytes, such as sorbitol and taurine, reduces the detrimental effects of high NaCl concentration in media used for the maturation of porcine oocytes. This effect is reflected by oocyte glutathione content and microfilament organization at the end of maturation and early development following in vitro maturation and in vitro fertilization.

SummaryPronuclear formation and intracellular content of glutathione, containing reduced and oxidised forms, in porcine oocytes matured in vitro were determined following insemination and/or electrical stimulation. After insemination, sperm penetration had occurred as early as 3 h and female pronuclei had formed by 6 h with complete development by 12 h. Male pronuclear formation occurred, primarily, between 9 and 12 h after insemination. Glutathione content of the oocytes decreased following sperm penetration and remained at a depressed level until 12 h. After electrical stimulation, oocyte activation had occurred and female pronuclei had formed by 3 and 6 h, respectively. Oocyte glutathione content did not change as a result of oocyte activation. When oocytes were exposed to an electrical pulse and then spermatozoa, female pronuclear formation was observed by 3 h after stimulation/insemination. Sperm penetration was observed between 3 and 9 h. However, the incidence of male pronuclear formation observed at 12 h was extremely low, although sperm decondensation had occurred in some oocytes. Oocyte glutathione content had not decreased by 6 h following electrical activation. These results demonstrate that the changes in glutathione content in porcine oocytes following fertilisation in vitro differ from those due to electrical activation. Further, the decreased intracellular glutathione content in oocytes activated by sperm penetration appears to be due to the presence of a sperm factor.

Porcine oocyte-cumulus complexes were cultured in bovine serum albumin (BSA)-free North Carolina State University (NCSU) 23 medium containing porcine follicular fluid (10%), cysteine (0.1 mg/ml) and hormonal supplements (eCG and hCG: lOIU/ml each) for 22h. They were then cultured in the same medium but without hormonal supplements for an additional 22 h. After culture, cumulus cells were removed and oocytes were co-incubated with frozen-thawed ejaculated boar spermatozoa in tissue culture medium (TCM) 199 containing caffeine (5 mM), fetal calf serum (FCS; 10%) and varying concentrations (26-56 mM) of NaHCO 3 for 9h (experiment 1). In experiment 2, chlortetracycline (CTC) was used to assess the functional state of spermatozoa incubated under different NaHCO 3 concentrations. Experiment 3 examined the effect of FCS (1% and 10%) and NaHCO 3 (26 and 46 mM) on fertilisation parameters. Compared with 26 mM, penetration rate was significantly higher (p < 0.05) at 36-56 mM NaHCO 3 . Polyspermy showed a similar pattern although no difference was observed between 26 and 36 mM. At 46 mM NaHCO 3 , the mean number of spermatozoa (MNS) penetrated per oocyte increased significantly (p<0.05). A significantly higher proportion of spermatozoa were capacitated and acrosome reacted at 46 and 56 mM NaHCO 3 , respectively. The fertilisation medium containing 46 mM NaHCO 3 and 1% FCS showed a higher penetration rate (84%) with a relatively low incidence of polyspermy (39%). The results indicate that NaHCO 3 stimulates capacitation and/or the acrosome reaction of boar spermatozoa in a dose-dependent manner and thus affects fertilisation parameters.