Quantification and distribution of equine oocyte cortical granules during meiotic maturation and after activation

In vitro fertilization (IVF) is being routinely used in humans and several domestic species, however, limited success has been achieved in the horse. Although immature equine oocytes are capable of completing meiosis in vitro, subsequent fertilization, and embryonic development of those oocytes are questionable. The lack of development of these oocytes could be attributed to an impaired cytoplasmic maturation. In the horse, the study of oocyte cytoplasmic maturation and post-fertilization development has been hindered by the lack of progress in IVF. In mammalian oocytes, migration of cortical granules (CG) has been used as an important criterion to evaluate cytoplasmic maturation. The aim of this study was to describe and quantify the CG distribution of equine oocytes during in vitro meiotic maturation and to assess activation of oocytes with calcium ionophore based upon fluorescein isothiocyanate (FITC)-labeled Lens culinaris agglutinin (LCA) and laser confocal microscopy. The results of this study indicate that CG are distributed throughout the cytoplasm of oocytes at the germinal vesicle (GV) stage (immature). As maturation proceeds, a progressive centripetal migration of CG to the oocyte cortex occurs with the formation of a monolayer adjacent to the plasma membrane starting by the end of a 30 hr incubation period and increasing significantly after 36 hr. After activation, significant reduction in the number of CG was observed (P < 0.001) suggesting that oocytes cultured under the present conditions possess the ability to release CG in response to the elevation of intracellular free calcium.     

Changes in cortical granules during porcine oocyte maturation

The structure, number, and distribution of cortical granules in porcine oocytes during maturation induced by human chorionic gonadotrophin (HCG) are reported. The number of granules remained constant for 30 hr following HCG. Thereafter, there was an approximate doubling by 50 hr. At all times examined, a dark and light form were present. Up to 40 hr the latter predominated while at 50 hr there was a marked increase in the number of the former. Movement of cortical granules to the plasma membrane took place between 20 and 30 hr post-HCG. The changes in cortical granules are correlated with the capacity of the oocytes to undergo a block to polyspermy.     

Quantitative studies of changes in cortical granule number and distribution in the mouse oocyte during meiotic maturation

Cortical granules (CGs) undergo a substantial change in distribution in the mouse oocyte cortex during meiotic maturation. In order to determine the mechanism of their change in distribution near the time of ovulation, CG density, total number per oocyte, and domain areas were quantitated. CGs were visualized microscopically by Lens culinaris agglutinin-biotin and Texas red-strepavidin fluorescence as well as by electron microscopy. Immature germinal vesicle stage (GV) oocytes from adult mice had a continuous cortical localization with some interior granules. Mature oocytes had an asymmetric cortical distribution with a CG-free domain, overlying the meiosis II metaphase spindle, occupying 40% of the cortex. The mean CG densities of the granule-occupied cortex of mature oocytes and the entire cortex of GV oocytes were 43 and 34 CGs/100 micron 2, respectively. The mean total numbers of CGs/oocyte were 4127 (mature) and 7440 (GV), and staining was absent in fertilized oocytes with two pronuclei. Calcium ionophore (A23187)-activated mature oocytes had a mean total number of 1235 CGs, some of which may have been in the process of exocytosis. The first polar body had few CGs, and thus was unlikely to account for the difference in CG number between GV and mature oocytes. The smaller total number and higher density of CGs in mature mouse oocytes suggests that both exocytosis and redistribution are plausible mechanisms for the development of the CG-free domain. Prefertilization exocytosis could account for the locus of sperm penetration which others have reported to occur in the hemisphere opposite the meiotic spindle in the mouse.     

Changes in histone acetylation during oocyte meiotic maturation in the diabetic mouse

Although there is considerable evidence that diabetes can adversely affect meiosis in mammalian oocytes, acetylation status of oocytes in a diabetic environment remains unclear. The objective was to determine acetylation or deacetylation patterns (based on immunostaining) of H3K9, H3K14, H4K5, H4K8, H4K12, and H4K16 sites at various stages during meiosis in murine oocytes from control and diabetic mice. According to quantitative real time polymerase chain reaction (qPCR), mean ± SEM relative expression of Gcn5 (1.70 ± 0.14 at metaphase [M]I and 1.27 ± 0.01 at MII, respectively), Ep300 (1.74 ± 0.04 at MI and 1.80 ± 0.001 at MII), and Pcaf (2.01 ± 0.03 at MI and 1.41 ± 0.18 at MII) mRNA in oocytes from diabetic mice were higher than those from controls (P < 0.05), whereas there was no difference (P > 0.05) during the germinal vesicle (GV) stage between the two groups (1.23 ± 0.04 for Gcn5, 0.82 ± 0.06 for Ep300, and 0.80 ± 0.07 for Pcaf). Conversely, relative mRNA expression concentrations of Hdac1, Hdac2, Hdac3, Sirt1 and Sirt2 during the germinal vesicle stage were lower in oocytes of diabetic mice (0.24 ± 0.03 for Hdac1, 0.11 ± 0.001 for Hdac2, 0.31 ± 0.03 for Hdac3, 0.28 ± 0.02 for Sirt1, and 0.55 ± 0.02 for Sirt2; P < 0.05). Similarly, the expression concentrations of these genes at the MI stage were lower in oocytes from diabetic mice (0.79 ± 0.12 for Hdac1, 0.72 ± 0.001 for Hdac2, 0.02 ± 0.001 for Sirt1, and 0.84 ± 0.08 for Sirt2; P < 0.05). Their expression concentrations at the MII stage were also lower in oocytes from diabetic mice (0.46 ± 0.03 for Hdac1, 0.93 ± 0.01 for Hdac2, 0.56 ± 0.01 for Hdac3, 0.01 ± 0.002 for Sirt1, and 0.84 ± 0.04 for Sirt2; P < 0.05). At the MI stage, however, there was no difference in the expression of Hdac3 between the two groups of oocytes (0.96 ± 0.03; P > 0.05). Taken together, diabetes altered the intracellular histone modification system, which may have contributed to changes in histone acetylation, and may be involved in the compromised maturation rate of oocytes in diabetic humans.     

Precocious loss of cortical granules during mouse oocyte meiotic maturation and correlation with an egg-induced modification of the zona pellucida

Fertilization results in cortical granule exocytosis, which is thought to be involved in modifications of the zona pellucida that constitute the zona pellucida block to polyspermy. A previous report demonstrated that a decrease in the number of Lens culinaris agglutinin-staining granules, which are likely to be cortical granules, occurred during in vivo mouse oocyte maturation with arrest at metaphase II, as well as the formation of a cortical granule-free domain in the area of the metaphase II spindle (T. Ducibella, E. Anderson, D.F. Albertini, J. Aalberg, and S. Rangarajan, 1988, Dev. Biol. 130, 184-197). We extend these observations by reporting here that germinal vesicle-intact oocytes matured in vitro to metaphase II in either the absence or the presence of serum develop a cortical granule-free domain and have reduced numbers of cortical granules when compared to germinal vesicle-intact oocytes; these changes are similar to those of oocytes matured in vivo. The reduction in the number of cortical granules requires germinal vesicle breakdown, since it is prevented by dibutyryl cAMP, which inhibits germinal vesicle breakdown in vitro. The ability of oocytes to respond to the calcium ionophore A23187 with a reduction in the number of cortical granules is also associated with meiotic maturation and develops between 7 and 12 hr after initiation of maturation. The maturation-associated reduction in the number of cortical granules is likely to represent cortical granule exocytosis, since this reduction is accompanied by the formation of a cortical granule-free domain and a conversion of ZP2 to ZP2f when the oocytes are matured in vitro in serum-free medium; this zona pellucida modification occurs following fertilization and is thought to be due to cortical granule exocytosis. In contrast, the loss of cortical granules and development of the cortical granule-free domain of oocytes matured in vitro in the presence of serum is not accompanied by the modification of ZP2. The inhibitory effect of serum on the ZP2 modification may afford in vivo a physiological mechanism to prevent a precocious modification of the zona pellucida that could result in a premature block to polyspermy and hence inhibit fertilization.     

Localization and function of mSpindly during mouse oocyte meiotic maturation

Spindly was first identified in Drosophila; its homologues are termed SPDL-1 in Caenorhabditis elegans and Hs Spindly/hSpindly in humans. In all species, Spindly and its homologues function by recruiting dynein to kinetochores and silencing SAC in mitosis of somatic cells. Depletion of Spindly causes an extensive metaphase arrest during somatic mitoses in Drosophila, C. elegans and humans. In Drosophila, Spindly is required for shedding of Rod and Mad2 from the kinetochores in metaphase; in C. elegans, SPDL-1 presides over the recruitment of dynein and MDF-1 to the kinetochores; in humans, Hs Spindly is required for recruiting both dynein and dynactin to kinetochores but it is dispensable for removal of checkpoint proteins from kinetochores. The present study was designed to investigate the localization and function of the Spindly homologue (mSpindly) during mouse oocyte meiotic maturation by immunofluorescent analysis, and by overexpression and knockdown of mSpindly. We found that mSpindly was typically localized to kinetochores when chromatin condensed into chromosomes after GVBD. In metaphase of both first meiosis and second meiosis, mSpindly was localized not only to kinetochores but also to the spindle poles. Overexpression of mSpindly did not affect meiotic progression, but its depletion resulted in an arrest of the pro-MI/MI stage, failure of anaphase entry and subsequent polar body emission, and in abnormal spindle morphology and misaligned chromosomes. Our data suggest that mSpindly participates in SAC silencing and in spindle formation as a recruiter and/or a transporter of kinetochore proteins in mouse oocytes, but that it needs to cooperate with other factors to fulfill its function.     

Distribution of prepubertal and adult goat oocyte cortical granules during meiotic maturation and fertilisation: ultrastructural and cytochemical study

The aim of this study was evaluate cortical granule (CG) distribution during in vitro maturation (IVM) and fertilisation of prepubertal goat oocytes compared to CG distribution of ovulated and in vitro fertilised oocytes from adult goats. Oocytes from prepubertal goats were recovered from a slaughterhouse and were matured in M199 with hormones and serum for 27 hr. Ovulated oocytes were collected from gonadotrophin treated Murciana goats. Frozen-thawed spermatozoa were selected by centrifugation in percoll gradient and were capacitated in DMH with 20% steer serum for 1 hr. Ovulated and IVM-oocytes were inseminated in DMH medium with steer serum and calcium lactate for 20 hr. Oocytes and presumptive zygotes were stained with FITC-LCA (Lens culinaris agglutinin labelled with fluorescein isothiocyanate) and observed under a confocal laser scanning microscope. Ultrastructure morphology of oocytes and presumptive zygotes were analysed by transmission electron microscopy (TEM). Prepubertal goat oocytes at germinal vesicle stage show a homogeneous CG distribution in the cytoplasm. IVM-oocytes at Metaphase II (MII) and ovulated oocytes presented CGs located in the cortex with the formation of a monolayer beneath to the plasma membrane. At 20 hr postinsemination (hpi), zygotes from IVM-oocytes showed a complete CG exocytosis whereas zygotes from ovulated oocytes presented aggregates of CGs located at the cortical region. Images by TEM detected that CGs were more electrodense and compacts in oocytes from prepubertal than from adult goats.     

Localization and function of the Ska complex during mouse oocyte meiotic maturation

The Ska (spindle and kinetochore-associated) complex is composed of three proteins: Ska1, Ska2 and Ska3. It is required for stabilizing kinetochore-microtubule (KT-MT) interactions and silencing spindle checkpoint during mitosis. However, its roles in meiosis remain unclear. The present study was designed to investigate the localization and function of the Ska complex during mouse oocyte meiotic maturation. Our results showed that the localization and function of Ska complex in mouse oocyte meiosis differ in part from those in mitosis. Injection of low dose exogenous Myc-Ska mRNA showed that, instead of localizing to the kinetochores (KTs) and mediating KT-MT interactions from pro-metaphase to mid-anaphase stages as in mitosis, the members of the Ska complex were only localized on spindle microtubules from the Pro-MI to MII stages in mouse oocyte meiosis. Time-lapse live imaging analysis showed that knockdown of any member of the Ska complex by Morpholino injection into mouse oocytes resulted in spindle movement defects and enlarged polar bodies. Depletion of the whole Ska complex disrupted the stability of the anaphase spindle and influenced the extrusion of the first polar body. Taken together, these results show that the Ska complex plays an important role in meiotic spindle migration and anaphase spindle stability during mouse oocyte maturation.     

Requirements of Src family kinase during meiotic maturation in mouse oocyte

The Src family kinase (SFK) is important in normal cell cycle control. However, its role in meiotic maturation in mammalian has not been examined. We used confocal microscope immunofluorescence to examine the in vitro dynamics of the subcellular distribution of SFK during the mouse oocyte meiotic maturation and further evaluated the functions of SFK via biochemical analysis using a specific SFK pharmacological inhibitor, PP(2). Our results showed that nonphospho-SFK was absent in oocyte upon its release from follicle. Nonphospho-SFK appeared in cytoplasm 0.5 hr after the release of oocyte and translocated to germinal vesicle (GV) before germinal vesicle breakdown (GVBD). After GVBD, nonphospho-SFK colocated with condensed chromosomes. In occyte at metaphase I (MI) and telophase I, nonphospho-SFK accumulated in the cortex and the cleavage furrow respectively besides its existence in cytoplasm in both stages. In oocyte at metaphase II (MII), nonphospho-SFK concentrated at the aligned chromosomes. In contrast, phospho-SFK was absent in oocyte until 1 hr after its release from the follicle. Phospho-SFK accumulated in the GV, the cortex, and cytoplasm immediately prior to GVBD. After GVBD, phospho-SFK evenly distributed in oocyte. In oocyte at MII, phospho-SFK localized throughout the cytoplasm and under the egg member. When the SFK activity was inhibited, the oocyte failed to initiate GVBD, could not go into MII, and could not extrude the first polar body. Our results demonstrated that SFK is required for meiotic maturation in mouse oocyte.     

Characterization of polo-like kinase 1 during meiotic maturation of the mouse oocyte

We have characterized plk1 in mouse oocytes during meiotic maturation and after parthenogenetic activation until entry into the first mitotic division. Plk1 protein expression remains unchanged during maturation. However, two different isoforms can be identified by SDS-PAGE. A fast migrating form, present in the germinal vesicle, seems characteristic of interphase. A slower form appears as early as 30 min before germinal vesicle breakdown (GVBD), is maximal at GVBD, and is maintained throughout meiotic maturation. This form gradually disappears after exit from meiosis. The slow form corresponds to a phosphorylation since it disappears after alkaline phosphatase treatment. Plk1 activation, therefore, takes place before GVBD and MAPK activation since plk1 kinase activity correlates with its slow migrating phosphorylated form. However, plk1 phosphorylation is inhibited after treatment with two specific p34(cdc2) inhibitors, roscovitine and butyrolactone, suggesting plk1 involvement in the MPF autoamplification loop. During meiosis plk1 undergoes a cellular redistribution consistent with its putative targets. At the germinal vesicle stage, plk1 is found diffusely distributed in the cytoplasm and enriched in the nucleus and during prometaphase is localized to the spindle poles. At anaphase it relocates to the equatorial plate and is restricted to the postmitotic bridge at telophase. After parthenogenetic activation, plk1 becomes dephosphorylated and its activity drops progressively. Upon entry into the first mitotic M-phase at nuclear envelope breakdown plk1 is phosphorylated and there is an increase in its kinase activity. At the two-cell stage, the fast migrating form with weak kinase activity is present. In this work we show that plk1 is present in mouse oocytes during meiotic maturation and the first mitotic division. The variation of plk1 activity and subcellular localization during this period suggest its implication in the organization and progression of M-phase.     

Relationship between growth and meiotic maturation of the mouse oocyte

Oocytes of various sizes were isolated from trypsinized ovaries of juvenile mice, cultured in a chemically defined medium, and scored for the resumption and completion of meiotic maturation. Oocytes recovered from mice younger than 15 days remained in the germinal vesicle stage, whereas those from mice 15 days or older resumed meiosis at a frequency which increased with the age of the mice. The mean diameter of the oocytes recovered also increased with the age of the mice. Within individual litters, the mean diameter of oocytes which failed to mature (incompetent oocytes) was significantly less than that of oocytes which matured (competent oocytes). The frequency of premature metaphase I arrest decreased markedly as the age of the mice and oocyte volume increased. These results suggest that the ability to resume meiosis is acquired at a specific stage of oocyte growth in the juvenile mouse, and that the ability to complete meiotic maturation is acquired subsequently. These oocytes provide an in vitro system with which to study the control of meiosis in the mammal.     

Changes in histone acetylation during postovulatory aging of mouse oocyte

Because some animals and human beings potentially engage in sexual activity at any day of the menstrual cycle, this may cause fertilization of postovulatory aged oocytes, which result in decreased potential of embryo development and longevity of offspring. To investigate the involvement of histone acetylation in the function of postovulatory aging, we examined the changes of histone acetylation by immunostaining with specific antibodies against various acetylated lysines on histones H3 and H4. We found that the acetylation levels of lysine 14 on histone H3 and lysines 8 and 12 on histone H4 in mouse oocytes were gradually increased during in vivo and in vitro postovulatory aging. Furthermore, the acetylation levels on these sites were markedly decreased or increased when the process of postovulatory aging was artificially delayed or accelerated, respectively. These results indicated that the gradual acetylation on some lysines of histones H3 and H4 is one of the phenomena in the process of postovulatory aging. Moreover, raising the level of histone acetylation by trichostatin A can accelerate the progression of postovulatory aging, suggesting that alteration of the acetylation on histones H3 and H4 can affect the progression of postovulatory aging in mouse oocytes.     

Regulation of meiotic metaphase by a cytoplasmic maturation-promoting factor during mouse oocyte maturation

During mouse oocyte maturation the regulation of the activity of a cytoplasmic maturation-promoting factor (MPF) was examined. The mouse MPF activity was determined based on its ability to induce maturation in immature starfish oocytes after microinjection with the cytoplasm from mouse oocytes. MPF appeared initially at germinal vesicle breakdown (GVBD), and its activity fluctuated in exact correspondence with meiotic cycles, reaching a peak at each metaphase and almost disappearing at the time of emission of the first polar body. Cycloheximide affected neither the initial MPF appearance nor GVBD. Thereafter, however, in the presence of cycloheximide the meiotic spindle was not formed and MPF disappeared, although the chromosomes remained condensed. After removing cycloheximide, MPF reappeared and was followed by the first metaphase and subsequently by polar body emission. Finally the meiotic cycle progressed to the second metaphase. Thus, for the appearance of MPF, there is a critical period shortly before the first metaphase, after which protein synthesis is required. In the presence of either cytochalasin D or colcemid, MPF activity remained at elevated levels. Addition of cycloheximide to such cytochalasin-treated oocytes, in which the meiotic cycle was arrested at the first metaphase, caused the MPF levels to decrease and was followed by movement of chromosomes to both poles where they decondensed and two nucleus-like structures were formed. Thus, the disappearance of MPF may initiate the metaphase-anaphase transition. Furthermore, detailed cytological examination revealed that chromosomes in cytochalasin-treated oocytes were monovalent while those treated only with cycloheximide were divalent, suggesting that dissociation of the synapsis is a prerequisite for chromosome decondensation after the disappearance of MPF. In all these respects, MPF seems to be a metaphase-promoting factor rather than just a maturation-promoting factor.     

SIRT4 is essential for metabolic control and meiotic structure during mouse oocyte maturation

SIRT4 modulates energy homeostasis in multiple cell types and tissues. However, its role in meiotic oocytes remains unknown. Here, we report that mouse oocytes overexpressing SIRT4 are unable to completely progress through meiosis, showing the inadequate mitochondrial redistribution, lowered ATP content, elevated reactive oxygen species (ROS) level, with the severely disrupted spindle/chromosome organization. Moreover, we find that phosphorylation of Ser293‐PDHE1α mediates the effects of SIRT4 overexpression on metabolic activity and meiotic events in oocytes by performing functional rescue experiments. By chance, we discover the SIRT4 upregulation in oocytes from aged mice; and importantly, the maternal age‐associated deficient phenotypes in oocytes can be partly rescued through the knockdown of SIRT4. These findings reveal the critical role for SIRT4 in the control of energy metabolism and meiotic apparatus during oocyte maturation and indicate that SIRT4 is an essential factor determining oocyte quality.     

In vivo activation of a microtubule-associated protein kinase during meiotic maturation of the Xenopus oocyte

We have characterized a serine/threonine protein kinase from Xenopus metaphase-II-blocked oocytes, which phosphorylates in vitro the microtubule-associated protein 2 (MAP2). The MAP2 kinase activity, undetectable in prophase oocytes, is activated during the progesterone-induced meiotic maturation (G2-M transition of the cell cycle). p-Nitrophenyl phosphate, a phosphatase inhibitor, is required to prevent spontaneous deactivation of the MAP2 kinase in crude preparations; conversely, the partially purified enzyme can be in vitro deactivated by the low-Mr polycation-stimulated (PCSL) phosphatase (also termed protein phosphatase 2A2), working as a phosphoserine/phosphothreonine-specific phosphatase and not as a phosphotyrosyl phosphatase indicating that phosphorylation of serine/threonine is necessary for its activity. S6 kinase, a protein kinase activated during oocyte maturation which phosphorylates in vitro ribosomal protein S6 and lamin C, can be deactivated in vitro by PCSL phosphatase. S6 kinase from prophase oocytes can also be activated in vitro in fractions known to contain all the factors necessary to convert pre-M-phase-promoting factor (pre-MPF) to MPF. Active MAP2 kinase can activate in vitro the inactive S6 kinase present in prophase oocytes or reactivate S6 kinase previously inactivated in vitro by PCSL phosphatase. These data are consistent with the hypothesis that the MAP2 kinase is a link of the meiosis signalling pathway and is activated by a serine/threonine kinase. This will lead to the regulation of further steps in the cell cycle, such as microtubular reorganisation and S6 kinase activation.     

The ability to achieve meiotic maturation in the dog oocyte is linked to glycolysis and glutamine oxidation

We tested the hypothesis that meiotic competence of dog oocytes is tightly linked with donor follicle size and energy metabolism. Oocytes were recovered from small (<1 mm diameter, n = 327), medium (1–<2 mm, n = 292) or large (≥2 mm, n = 102) follicles, cultured for 0, 24, or 48 hr, and then assessed for glycolysis, glucose oxidation, pyruvate uptake, glutamine oxidation, and nuclear status. More oocytes (P < 0.05) from large follicles (37%) reached the metaphase‐II (MII) stage than from the small group (11%), with the medium‐sized class being intermediate (18%; P > 0.05). Glycolytic rate increased (P < 0.05) as oocytes progressed from the germinal vesicle (GV) to MII stage. After 48 hr of culture, oocytes completing nuclear maturation had higher (P < 0.05) glycolytic rates than those arrested at earlier stages. GV oocytes recovered from large follicle oocytes had higher (P < 0.05) metabolism than those from smaller counterparts at culture onset. MII oocytes from large follicles oxidized more (P < 0.05) glutamine than the same stage gametes recovered from smaller counterparts. In summary, larger‐sized dog follicles contain a more metabolically active oocyte with a greater chance of achieving nuclear maturation in vitro. These findings demonstrate a significant role for energy metabolism in promoting dog oocyte maturation, information that will be useful for improving culture systems for rescuing intraovarian genetic material. Mol. Reprod. Dev. 79: 186–196, 2012. Published 2011. This article is a U.S. Government work and is in the public domain in the USA.     

A C-type lectin associated and translocated with cortical granules during oocyte maturation and egg fertilization in fish

Oocyte maturation and egg fertilization in both vertebrates and invertebrates are marked by orchestrated cytoplasmic translocation of secretory vesicles known as cortical granules. It is thought that such redistribution of cellular content is critical for asymmetrical cell division during early development, but the mechanism and regulation of the process is poorly understood. Here we report the identification, purification and cDNA cloning of a C-type lectin from oocytes of a freshwater fish species gibel carp (Carassius auratus gibelio). The purified protein has been demonstrated to have lectin activity and to be a Ca(2+)-dependent C-type lectin by hemagglutination activity assay. Immunocytochemistry revealed that the lectin is associated with cortical granules, gradually translocated to the cell surface during oocyte maturation, and discharged to the egg envelope upon fertilization. Interestingly, the lectin becomes phosphorylated on threonine residues upon induction of exocytosis by fertilization and returns to its original state after morula stage of embryonic development, suggesting that this posttranslational modification may represent a critical molecular switch for early embryonic development.     

Intramitochondrial transformations during oocyte maturation in the mouse

An electron microscope study of oocyte maturation in the mouse revealed that some mitochondria undergo gradual transformation in their ultrastructural appearance. In very young oocytes these mitochondria were already found to contain vacuoles, one in each such organelle. In somewhat older oocytes more mitochondria displayed vacuoles which generally appeared to be getting larger. These intramitochondrial vacuoles were found to be essentially optically empty structures surrounded by a single membrane. In favorable sections someof the developing vacuoles had a bottle-shaped appearance, the constricted end of which was attached to the inner limiting membrane of the mitochondrion. With further maturation of the oocytes vacuoles having a pear-shaped appearance became evident. An hypothesis was presented outlining the mode of formation of these vacuoles by expansion of the individual cristae. Intramitochondrial transformations occuring during both oogenesis and spermatogenesis in mammals were reviewed.     

雷公藤多甙对小鼠卵母细胞成熟和体外受精的影响

采用超排卵技术研究雷公藤多甙（GTW）对小鼠卵母细胞的成熟和体外受精以及脏器等的影响,GTW对小鼠卵母细胞生发泡破裂没有影响,但可以抑制卵母细胞第一极体的释放,影响卵母细胞的存活率并可降低体外受精率和超排卵的卵母细胞数量。GTW可以破坏卵母细胞成熟,降低卵母细胞的体外受精能力,影响小鼠的正常生殖功能。     

Calcium and meiotic maturation of the mammalian oocyte

The role of calcium in the regulation of both the meiotic and mitotic cell cycles has been the subject of considerable investigation in the nonmammalian field. In contrast, the mechanisms for signalling meiotic maturation in the mammalian oocyte are not as well documented nor as clearly defined. In the mammalian oocyte, calcium is associated with both spontaneous and hormone-induced meiotic maturation. A transient release of endogenously stored calcium precedes germinal vesicle breakdown and can override cyclic AMP maintained meiotic arrest; it thus may signal the resumption of meiosis. Additionally, extracellular calcium is apparently required for meiotic progression past metaphase I. The time sequence for meiotic resumption and progression is very varied between species. The timing of cell cycle protein synthesis during meiosis suggests that cyclins may be expressed in oocytes of some species much earlier in their development than in others. A generic model is proposed for the mechanism for triggering meiotic resumption in the mammalian oocyte. In this model, the critical components of meiotic resumption involve the temporal relationship of cyclin synthesis and the subsequent activation of the MPF complex by the calcium signal generated, which accounts for differences among species. © 1995 Wiley-Liss, Inc.