Hum. Reprod. Advance Access originally published online on February 12, 2004
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Human Reproduction, Vol. 19, No. 4, 982-987,
April 2004
© 2004 European Society of Human Reproduction and Embryology
Time-dependent capability of human oocytes for activation and pronuclear formation during metaphase II arrest
1 CReATe Program Inc. and 2 Department of Obstetrics and Gynecology, Sunnybrook and Women’s College Health Sciences Center, University of Toronto, Toronto, Ontario, Canada
3 To whom correspondence should be addressed at CReATe Program Inc., 790 Bay Street, Suite 1020, Toronto, Ontario, M5G 1N8 Canada. e-mail: hbalakier{at}sympatico.ca
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and methodsResultsDiscussionReferences |
|---|
BACKGROUND: The purpose of this study was to investigate the fertilization rate and developmental potential of human oocytes in relation to the duration of their metaphase II (MII) arrest stage following the extrusion of the first polar body (1PB). METHODS: Immature metaphase I oocytes (MI; study oocytes, n = 468) that underwent meiotic maturation during brief in vitro culture and their matured in vivo, MII siblings (control oocytes, n = 3293) were subjected to ICSI. Fertilization and early cleavage were evaluated in both study and control groups. RESULTS: The overall fertilization rate was significantly lower in the oocytes matured in vitro than in those matured in vivo (42 versus 77%, P < 0.0001). A significant relationship was observed between oocyte activation potential and the length of MII arrest. The majority of study oocytes injected soon after PB extrusion remained unfertilized (64%; 98/154 oocytes). The proportion of normally activated oocytes that contained two pronuclei and two PBs gradually increased with prolonged time of MII arrest (43 and 61% at 2 and 3–6 h after 1PB extrusion). Significantly more embryos originating from the study than control oocytes were arrested soon after the first two cleavage divisions (39 and 17%; P < 0.0001) and exhibited multinucleated blastomeres (23 and 13%; P < 0.0001), which suggests the existence of chromosomal abnormalities. CONCLUSIONS: Human oocytes progressively develop the ability for full activation and normal development during the MII arrest stage.
Key words: cytoplasmic maturation/metaphase II arrest/multinucleation/metaphase I oocytes/oocyte activation
|
Introduction |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
The timing of maturational events appears to be tightly regulated and crucial for the gradual acquisition of oocyte developmental competence (Eppig, 1996
; Moor et al., 1998; Trounson et al., 2001; Albertini, 2003). It is now commonly recognized that complete oocyte maturation not only depends on nuclear meiotic progression and DNA remodelling, but is also critically influenced by the quality and maturity of ooplasm and alterations of the plasma membrane system (Ji et al., 1997; Bao et al., 2000; Liu et al., 2001). Data from animal and human studies indicate that the molecular programme for development of growing oocytes is assembled for continuous synthesis of various proteins and mRNAs, some of which are expressed throughout the follicular phase while others are masked until or after meiotic progression to metaphase II (MII) arrest (Schultz et al., 1988; Masui, 1992; Gondolfi and Gondolfi, 2001; Trounson et al., 2001; Josefsberg and Dekel, 2002; Gosden, 2002). The maturational period also involves the development of very specific and precise mechanisms, which enable the storage and timely use of these molecules. To accomplish this, maturing oocytes undergo significant structural reorganization of cytoplasmic organelles in the cytoskeleton (reviewed by Albertini, 2003). They also become capable of rapid post-transcriptional and post-translational modifications and acquire a full complement of Ca2+ signalling molecules (Carroll, 2001; Josefsberg and Dekel, 2002).
Interestingly, experiments on mouse and bovine oocytes indicate that the process of oocyte maturation is not completed upon reaching the MII stage (Kubiak, 1989; Dominko and First, 1997). It is suggested that oocyte maturation involves two equally important time requirements that determine the oocyte developmental competence and the ability to produce a viable embryo. The first period is required for oocytes to resume meiosis and progress to the MII stage, and the second period corresponds to the time interval between MII arrest and sperm activation. It was shown that mouse and bovine MII oocytes gradually develop the ability for activation and pronuclear formation (Kubiak, 1989; Dominko and First, 1997). Therefore, essential cytoplasmic changes may be taking place during the MII arrest period and thus successful embryo development depends on proper timing of oocyte maturation as well as oocyte fertilization. Early studies on fertilizability of human oocytes as well as recent reports on development of in vitro matured human MI oocytes suggest that MII oocytes require additional time for maturation in order to be activated promptly by the fertilizing spermatozoon (Lopata and Leung, 1988; Bonada et al., 1996; DeVos et al., 1999; Huang et al., 1999).
Since there is no direct evidence available with respect to the time period needed for oocyte maturation after MII arrest in humans, the purpose of this study was to evaluate the fertilization rates and developmental potential of human oocytes subjected to ICSI at different times after extrusion of the first polar body (1PB). To achieve this goal, human immature metaphase I (MI) oocytes, acquired after ovarian stimulation, that progressed to the MII stage within a few hours of in vitro culture were compared with sibling oocytes which had matured in vivo, with respect to normal zygote formation, subsequent cleavage and embryo quality.
|
Materials and methods |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Our study included 326 patients who underwent gonadotrophin stimulation followed by oocyte retrieval and fertilization of their oocytes by ICSI (each patient was included only once in the study, regardless of cycle number). Patient selection was based on the presence of immature MI oocytes capable of in vitro maturation (IVM) during the first 3 h of in vitro culture, which allowed their ICSI at the same time as their sibling, MII mature oocytes. Patients whose MI oocytes were incapable of IVM or patients whose MI oocytes extruded the 1PB after >3 h of incubation were excluded from the study. The women ranged in age from 29 to 41 years with a mean age of 34.2 years. Ovarian stimulation was induced in the standard way, using a combination of long acting GnRH agonist (Lupron; Abbott Laboratories Ltd, Montreal, Quebec, Canada) along with daily administration of HMG (Pergonal or Gonal-F from Serono Canada Inc., Mississauga, Ontario, Canada; and Puregon from Organon Canada Ltd, Scarborough, Ontario, Canada). Oocytes were retrieved by transvaginal aspiration under ultrasound guidance 36–38 h after the injection of HCG (Profasi HP; Serono). Following retrieval, the oocytes were briefly exposed to 80 IU/ml hyaluronidase (Type IV-S, Sigma, St Louis, MO) and mechanically cleaned from their surrounding corona– cumulus cells. Nuclear maturity of the oocytes was carefully examined under an inverted microscope at x320 magnification (Leitz DMIL, relief contrast, Leica, Richmond Hill, Ontario, Canada). Matured MII oocytes were identified by the presence of 1PB and were immediately separated from immature germinal vesicle (GV) stage oocytes and MI oocytes that had already undergone the GV breakdown but had not extruded the 1PB. The MI oocytes were cultured further in vitro for a maximum of 3 h and during this time they were monitored every 30 min for the progression of their meiotic maturation (oocytes that matured later were not included in the study). ICSI for each patient was performed on two types of oocytes. The first group consisted of MI oocytes that reached the MII stage (MI
MII) after in vitro culture and they will be referred to here as study oocytes. The second, control group consisted of sibling oocytes that were recovered at the MII stage during the procedure of oocytes denudation, performed either immediately or within 1–2 h after retrieval (the majority at 1 h). Control oocytes were subjected to ICSI within 1–6 h of culture, whereas MIMII study oocytes were injected at three different time intervals after reaching the MII arrest stage. The intervals were as follows: (i) 1–1.5 h; (ii) 2–2.5 h; and (iii) 3–6 h after PB extrusion as a sign of completion of oocyte nuclear maturation. Distribution of the study oocytes into these groups was random. Oocyte incubation prior to and following sperm injection, as well as embryo culture, were performed in IVC-One medium (In vitro Care Inc., San Diego, CA) supplemented with 10% SSS (synthetic serum supplement; Somagen, Edmonton, Alberta, Canada) under mineral oil (Sigma) at 37°C in an atmosphere of 5% CO2, 5% O2 and 90% N2. All semen samples were obtained from ejaculates and in all cases sufficient motile spermatozoa were recovered using Pure Sperm density gradient separation (MediTech, Montreal, Quebec, Canada). Severe cases of oligospermia were excluded from this study.
Assessment of fertilization took place 16–18 h after the ICSI procedure and oocytes containing two pronuclei (2PN) and two PBs were considered as normally fertilized. The cleavage stage and embryo morphology were evaluated 24 and 48 h later (day 2 and day 3 of development). For each embryo, the number and size of the blastomeres and the percentage of anucleated fragments were recorded. The presence of multinucleated blastomeres (MNBs) per embryo was also observed but not included in the embryo scoring system. Good quality embryos were defined as embryos with a maximum of 20% fragmentation and equal or unequal sized blastomeres. Embryos with >20% but <50% of anucleated fragments were categorized as fair, and those with >50% fragmentation were considered poor. Only good and fair embryos were transferred back to patients 72 h after oocyte retrieval (day 3). The luteal phase was supported by either micronized vaginal progesterone (Medicine Shoppe, Toronto, Ontario, Canada) or progesterone in oil (Cytex Pharmaceuticals Inc., Halifax, Nova Scotia, Canada).
In some cases, in vitro matured MIMII oocytes that had failed fertilization after ICSI were analysed on air-dried preparations to determine the presence and nuclear status of the spermatozoa within oocyte cytoplasm. According to the method described by Kamiguchi et al. (1993), the zona pellucida was removed by acid Tyrode solution (pH 2, Sigma) and the oocytes were treated with hypotonic 0.5% sodium citrate (Sigma) for 10 min followed by gradual fixation and staining with Giemsa.
Statistical comparisons of the fertilization rates, embryo cleavage and embryo quality between the study and control groups were determined by the 
2 and Fisher’s exact test as appropriate. The Cochran–Armitage trend test was also used to analyse trends in the changes in fertilization and cleavage rates in oocytes/embryos originating from in vitro matured MIMII oocytes.
|
Results |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
A total of 4844 oocytes were collected from 326 ICSI patients. Overall, 3293 of retrieved oocytes were mature in the MII stage and 604 oocytes remained at the MI stage of the first meiotic division at the time of removal of the corona–cumulus cells (mean 1.9 MI oocyte/patient, range 1–6). Among 468 immature MI oocytes, 90 (19%), 182 (39%), 168 (36%) and 28 (6%) oocytes underwent maturation and extruded the 1PB during 30 min, 1, 2 and 3 h of in vitro culture, respectively. It was found that the extrusion of the 1PB is a relatively fast event that may occur within 30 min during the interval between subsequent observation periods. Based on this observation, it is possible that some oocytes completed their maturation just after retrieval and were incorporated into the control group, even though oocyte denudation was usually performed shortly after oocyte collection. Nevertheless, the control group will be considered here as a group of in vivo matured oocytes. In each cycle, both in vitro matured MI
MII, study oocytes, and their siblings, in vivo matured MII control oocytes, were injected with patient’s sperm. The fertilization rates and morphology of the zygotes are shown in Table I. Overall, the fertilization rate of in vitro matured oocytes was significantly lower (42%) than that of control oocytes (77%; P < 0.0001). In the study group, the proportion of fertilized to unfertilized oocytes showed a highly significant trend in relation to the time of the ICSI procedure after PB extrusion (P < 0.0001). Only 25% of oocytes injected shortly after reaching the MII stage were normally fertilized and contained 2PN and 2PBs. However, with prolonged time in culture, the frequency of binuclear zygotes increased considerably and the following fertilization rates were recorded: 43% at 2–2.5 h after PB extrusion, 59% at 3–3.5 h and 62% at 4–6 h. Since no statistical difference was observed between the last two time intervals, the results were pooled together and presented as one group (3–6 h; Table I). Therefore, it appears that 3–4 h of incubation after extrusion of the 1PB is sufficient to obtain a plateau of reasonable fertilization results. It should be noted that in the control group, 18, 60 and 22% of MII oocytes were injected at 1, 2 and 3–6 h after corona cell removal; however, the fertilization rates were similar regardless of the time interval of the ICSI procedure (80, 73 and 78%, respectively). The in vitro matured MI oocytes also showed an increased incidence of abnormal fertilization including three-pronuclear (3PN; 22/468) and one-pronuclear (1PN; 26/468) oocytes, compared with the in vivo matured MII sibling oocytes (3PN; 103/3293 and 1PN; 66/3293; in total 10 versus 5%, respectively; P < 0.0001, Table I).
|
Air-dried preparations made from 31 MI
MII study oocytes that failed to show morphological evidence of fertilization 24 h after ICSI indicated correct sperm injection in all examined oocytes (ICSI at 1–3 h after PB extrusion). Even though the oocytes remained non-activated, they contained, in addition to the maternal set of MII chromosomes, either condensed sperm heads (5/31; 16%) or prematurely condensed sperm chromosomes in the form of single chromatids (26/31; 84%). In 16 out of 26 oocytes, the two types of chromosomes were located in separate metaphase plates (Figure 1A and B), while in 10 oocytes they were mixed together in one common group of chromosomes (Figure 1C). It should be mentioned that the majority of non-activated, study oocytes exhibited a single PB (164/216; 76%), 19% of oocytes had a fragmented PB and 5% of oocytes displayed two distinct PBs.
|
In both the study and control groups, the rates of the first cleavage division were comparable and almost all zygotes had formed 2-cell embryos (95 and 96%, respectively). However, further embryo development was significantly different (Table II). A high proportion of embryos obtained from in vitro matured MI oocytes were arrested at the 2- and 4-cell stage on day 3 of development, compared with the control group derived from in vivo matured MII oocytes (39 and 17%; P < 0.0001). Consequently, fewer embryos reached more advanced developmental stages (5–6 cells and 8–9 cells) in the study than in the control group (20 and 33% versus 31 and 43%; respectively, P < 0.0001). The quality of embryos, measured by the size of cells and the percentage of anuclear fragmentation, did not really differ between the groups, and similar proportions of good, fair and poor quality embryos were observed (55, 35 and 10% in the study group and 61, 27 and 12% in the control group; P = 0.0846). The only significant difference in embryo quality was related to the presence of MNBs (Table II). This nuclear abnormality was nearly double in the embryos derived from in vitro matured MI
MII oocytes when compared with embryos from the control group of in vivo matured MII oocytes (23 and 13%; P < 0.0001). An increased incidence of MNBs was observed in the embryos when ICSI was performed shortly after PB extrusion (36%, Table II). This difference was statistically significant when these embryos were compared with the other embryos from later time intervals (P = 0.006 and P = 0.017 when groups one versus two and one versus three were analysed, respectively).
|
Embryos originating from in vitro matured MI
MII oocytes were rarely chosen for uterine replacements. No pregnancies were obtained from four exclusive transfers of study embryos derived from in vitro matured MI oocytes (three embryo transfers with one embryo, and one embryo transfer with two embryos). In the other 16 cases, mixed embryos from both the study (n = 16) and control (n = 46) groups were used, resulting in five singleton pregnancies (one study embryo/each patient). Single embryos from the study group were also frozen for 21 patients and used later after thawing in mixed transfers (21 study/67 control embryos). Three singleton pregnancies from those frozen–thawed cycles were established. |
Discussion |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Ovulated oocytes of various animal species display a time-dependent increase in their ability to undergo activation after IVF or experimental manipulations with activating agents (Fulton and Whittingham, 1978
; Kubiak, 1989; Ware et al., 1989; Fissore and Robl, 1992; Dominko and First, 1997; Xu et al., 1997). Compared with newly ovulated MII oocytes, those which are activated several hours after ovulation exhibit much higher potential for full activation defined by completion of the second meiotic division and pronuclear formation. Similarly, in humans, fertilization rates are considerably enhanced when insemination is delayed for several hours (3–6 h) after oocyte retrieval (Trounson et al, 1982). Furthermore, experiments on mice indicated that oocytes activated soon after reaching the MII stage respond abortively by extrusion of the 2PBs followed by another metaphase arrest, called metaphase III (MIII; Kubiak, 1989). It was also observed that with prolonged duration of the MII stage, mouse oocytes gradually gain the capacity to enter into zygotic interphase. Therefore, it has been concluded that freshly ovulated oocytes remain cytoplasmicly immature and require additional changes to support fertilization and further development (Kubiak, 1989).
The results of this study strongly agree with the above observations on animal oocytes. Likewise, we demonstrated that human matured oocytes progressively develop the ability for full activation and pronuclear formation during their MII arrest following the extrusion of the 1PB. In the present study, the overall fertilization rate after ICSI of in vitro matured MI oocytes was significantly reduced when compared with that observed in sibling oocytes matured in vivo (42 versus 77%; Table I). This correlates well with the recent reports on lower fertilization rates obtained from human MI oocytes which had matured in culture within 4–8 h; however, the exact time of PB extrusion was not recorded in these studies (Bonada, 1996; DeVos et al., 1999; Huang et al., 1999). Our detailed analysis of the data with regards to the time interval between PB extrusion and sperm injection revealed a significant relationship between the oocyte activation potential and the duration of MII arrest. It was found that the vast majority of in vitro matured MI oocytes injected soon after PB extrusion remained unfertilized (64%; Table I) and the proportion of normally activated oocytes that contained 2PN and 2PBs gradually increased with prolonged time of incubation before the ICSI procedure. The oocytes injected 
1 and 2 h after MII arrest gave rise to 25 and 43% zygote formation, while delayed ICSI for 3 or 4–6 h resulted in 59 and 62% fertilization rates, respectively. This may suggest that a minimum of 3 h of MII arrest is required to obtain reasonable fertilization rates comparable with those recorded for the control group of oocytes (77%; Table I). These observations can be utilized in future studies to determine the time of ICSI to achieve optimum fertilization and development of in vitro matured human oocytes (non-stimulated cycles). It was shown recently that in vitro matured oocytes are sensitive to post-maturation ageing, and delayed sperm injection (after 36 h versus 30 h culture) results in a high incidence of pronuclear abnormalities (presence of 1PN, asynchrony in size; Goud et al., 1999). Experiments on bovine oocytes also indicated that prolonged MII arrest before insemination leads to a gradual loss of the ability to support fertilization and embryo development (Dominko and First, 1997). Therefore, defining the appropriate duration of MII arrest and the time of ICSI may be crucial for the best results in human IVM.
Oocyte immaturity is associated with the failure of oocyte activation as well as with the occurrence of sperm premature chromosome condensation (PCC) after insemination or ICSI (reviewed by Plachot, 1995). Currently, this relationship is well documented in mouse oocytes and it is assumed to be true for human oocytes, although definitive experiments were not carried out for obvious reasons (Calafell et al., 1991; Kovacic and Vlaisavljevic, 2000; Benkhalifa, 2003). Using a murine model, a high incidence of PCC (46%) was only observed when freshly formed MII oocytes were retrieved from ovaries just before ovulation and immediately fertilized in vitro (Calafell et al., 1991). In human IVF programmes, the frequency of this phenomenon varies from 4 to 28% and it appears to be higher in immature MI (34%) than mature MII oocytes (14%; see Plachot, 1995). Analysis of our cytological data obtained from unfertilized oocytes following ICSI provides good evidence for the notion that cytoplasmic immaturity is the main factor causing sperm PCC in human oocytes. Nearly all non-activated oocytes (84%; others contained condensed sperm heads) that were injected 1 or 3 h after the 1PB extrusion showed the presence of sperm chromosomes located near the meiotic spindle or mixed together with maternal chromosomes. Alternatively, the lack of oocyte activation may also be due to the absence or deficiency of sperm-activating factor (Dozortsev et al., 1997). However, this explanation seems to be rather far-fetched because the control sibling oocytes injected with the same sperm samples always exhibited high fertilization rates (77%, Table I). It is therefore clear that specific changes must take place to enable the MII oocytes to be activated.
From the molecular point of view, there are at least two mitotic kinases: maturation-promoting factor (MPF) and mitogen-activated protein kinase (MAPK), which play a significant role in maintenance of and exit from the MII stage (reviewed by Alberio et al., 2001). It appears that inactivation of both kinases is required for matured oocytes to be normally activated and progress through pronuclear interphase, which seems to be controlled via two independent mechanisms (Liu et al., 1998; Alberio et al., 2001). Interestingly, recent studies also demonstrated that abortive oocyte activation (i.e. formation of MIII arrest; Liu et al., 1998) and Ca2+ transients at fertilization (reviewed by Carroll, 2001) depend on mutual activities of MPF and MAPK. Therefore, based on current accumulated data, it can be speculated that final cytoplasmic maturation of human MII-arrested oocytes may depend on complex interactions between MPF and MAPK as well as on their association with the other protein kinases and calcium mechanisms that are essential for oocyte fertilization and successful embryo development.
The effects of cytoplasmic deficiencies occurring during oocyte maturation may be expressed either by lack of oocyte activation or by a failure of early preimplantation development (Moor et al., 1998). Here we showed that the developmental capacity of human embryos derived from in vitro matured MI oocytes was significantly reduced compared with those developed from the control sibling oocytes. A high proportion of study embryos were arrested soon after the first or the second cleavage division (at the 2- and 4-cell stage). Also a significantly large number of those embryos exhibited the presence of MNBs, suggesting the existence of chromosomal aberrations. These results remain in agreement with the recent studies in which early embryo arrest and a high incidence of MNBs and aneuploidy were observed in human embryos derived from in vitro matured GV and MI oocytes retrieved from stimulated cycles (Nogueira et al., 2000; Lundin et al., 2002). The authors suggest that such developmental abnormalities may arise from some deficiencies in oocyte maturation that lead to spindle defects which results in abnormal cytokinesis, formation of MNBs and chromosomal aberrations. Previous animal studies have indicated frequent chromatin aberrations in oocytes inseminated immediately after MII arrest and their decreased development to blastocyst stage, implicating similar spindle problem(s) (Dominko and First, 1997). In fact, recent experiments on mouse and bovine oocytes demonstrated the importance of MAPK in regulating MII spindle assembly and stability (Verlhac et al., 1993; Araki et al., 1996; Gordo et al., 2001). It was shown that MAPK associates with the spindle poles of MI and MII. The oocytes deprived of its activity exhibit disorganized meiotic spindles and poorly aligned chromosomes. It is clear that in animal and human oocytes, one of the profound changes that take place during the early phase of MII arrest relates to the spindle formation and its function.
Full developmental competence of in vitro matured human oocytes is severely compromised, although rare cases of live births have been reported (Cha and Chian, 1998; Trounson et al., 2001). In this respect, the results of our study remain inconclusive because no pregnancies were established from embryos derived exclusively from MI study oocytes, while the other pregnancies resulted from the mixed transfers when embryos from MI and MII sibling oocytes were combined. However, development to term of in vitro matured GV and MI oocytes, retrieved from stimulated cycles, is possible, as was proven by DeVos (one singleton; implantation rate 5.3%; DeVos et al., 1997) and others (reviewed by Cha and Chian, 1998).
In conclusion, final maturation of human MII-arrested oocytes is crucial for the acquisition of the ability to undergo normal activation and cleavage divisions. This period seems to be important for assembly and normal function of the meiotic spindle. Developmental capacity of embryos originating from in vitro matured MI oocytes is significantly reduced. Caution should be exercised when using MI oocytes for application in assisted reproductive technology programmes, considering the high probability of chromosomal abnormalities in those embryos (minimum 4–6 h of culture after PB extrusion, observation of MNBs). The improvement of culture conditions and defined ICSI timing may enhance the results of the human IVM system.
|
Acknowledgements |
|---|
The material of this study was collected at the START IVF clinic and we would like to thank all staff members for their kind assistance. We also would like to thank Ms Jana Karaskova for her technical help with photography, Mr Rahim Moineddin for statistical analysis of the data, and Ms Jackilynn Rogers for critical reading of the manuscript. The results of this study were presented at the 59th Annual Meeting of the American Society for Reproductive Medicine, San Antonio, Texas, USA, October 11–15, 2003.
|
References |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Alberio R, Zakhartchenko V, Motlik J and Wolf E (2001) Mammalian oocyte activation: lessons from the sperm and implications for nuclear transfer. Int J Dev Biol 45,797–809.[Web of Science][Medline]
Albertini DF (2003) Origins and manifestation of oocyte maturation competencies. RBM Online 6,410–415.
Araki K, Naito K, Haraguchi S, Suzuki R, Yokoyama M, Inoue M, Aizawa S, Toyoda Y and Sato E (1996) Meiotic abnormalities of c-mos knockout mouse oocytes: activation after first meiosis or entrance into third meiotic metaphase. Biol Reprod 55,1315–1324.[Abstract]
Bao S, Obata Y, Carroll J, Domeki I and Kono T (2000) Epigenetic modifications necessary for normal development are established during oocyte growth in mice. Biol Reprod 62,616–621.
Benkhalifa M, Kahraman S, Caserta D, Domez E and Qumsiyeh MB (2003) Morphological and cytogenetic analysis of intact oocytes and blocked zygotes. Prenat Diagn 23,397–404.[CrossRef][Web of Science][Medline]
Bonada M, Cremades N, Alvarez C, Bernabeu R, Llacer J and Bernabeu S (1996) ICSI on metaphase I oocytes matured in vitro [abstract P090]. Hum Reprod (Abstract Book) 11,136.
Calafell JM, Badenas J, Egozcue J and Santalo J (1991) Premature chromosome condensation as a sign of oocyte immaturity. Hum Reprod 6,1017–1021.
Carroll J (2001) The initiation and regulation of Ca2+ signaling at fertilization in mammals. Cell Dev Biol 12,37–43.
Cha KY and Chian RC (1998) Maturation in vitro of immature human oocytes for clinical use. Hum Reprod Update 4,103–120.
DeVos A, Van de Velde H, Joris H and Van Steirteghem A (1999) In-vitro matured metaphase-I oocytes have a lower fertilization rate but similar embryo quality as mature metaphase-II oocytes after intracytoplasmic sperm injection. Hum Reprod 14,1859–1863.
Dominko T and First NL (1997) Timing of meiotic progression in bovine oocytes and its effect on early embryo development. Mol Reprod Dev 47,456–467.[CrossRef][Web of Science][Medline]
Dozortsev D, Qian C, Ermilov A, Rybouchkin A, DeSutter P and Dhont M (1997) Sperm-associated oocyte-activating factor is released from the spermatozoon within 30 minutes after injection as a result of the sperm–oocyte interaction. Hum Reprod 12,2792–2796.
Eppig JJ (1996) Coordination of nuclear and cytoplasmic oocyte maturation in Eutherian mammals. Reprod Fertil Dev 8,485–489.[CrossRef][Medline]
Fissore RA and Robl JM (1992) Intracellular Ca2+ response of rabbit oocytes to electrical stimulation. Mol Reprod Dev 32,9–16.[CrossRef][Web of Science][Medline]
Fulton BP and Whittingham DG (1978) Activation of mammalian oocytes by intracellular injection of calcium. Nature 273,149–151.[CrossRef][Medline]
Gondolfi T and Gondolfi F (2001) The maternal legacy to the embryo: cytoplasmic components and their effects on early development. Theriogenology 55,1255–76.[CrossRef][Web of Science][Medline]
Gordo AC, He CL, Smith S and Fissore RA (2001) Mitogen activated protein kinase plays a significant role in metaphase II arrest, spindle morphology, and maintenance of maturation promoting factor activity in bovine oocytes. Mol Reprod Dev 59,106–114.[CrossRef][Web of Science][Medline]
Gosden RG (2002) Oogenesis as a foundation for embryogenesis. Mol Cell Endocinol 186,149–153.[CrossRef][Web of Science][Medline]
Goud P, Goud A, Van Oostveldt P, Van der Elst J and Dhont M (1999) Fertilization abnormalities and pronucleus size asynchrony after intracytoplasmic sperm injection are related to oocyte postmaturity. Fertil Steril 72,245–252.[CrossRef][Web of Science][Medline]
Huang FJ, Chang SY, Tsai MY, Lin YL, Kung FT, Wu JF and Lu YJ (1999) Relationship of human cumulus-free oocyte maturational profile with in vitro outcome parameters after intacytoplasmic sperm injection. J Assist Reprod Genet 16,483–487.[CrossRef][Web of Science][Medline]
Ji YZ, Bomsel M, Jouannet P and Wolf JP (1997) Modification of the human oocyte plasma membrane protein pattern during preovulatory maturation. Mol Reprod Dev 47,120–126.[CrossRef][Web of Science][Medline]
Josefsberg LB and Dekel N (2002) Translational and post-translational modifications in meiosis of the mammalian oocyte. Mol Cell Endocrinol 22,161–171.
Kamiguchi Y, Rosenbusch B, Sterzik K and Mikamo K (1993) Chromosomal analysis of unfertilized human oocytes prepared by a gradual fixation–air drying method. Hum Genet 90,533–541.[CrossRef][Web of Science][Medline]
Kovacic B and Vlaisavljevic V (2000) Configuration of maternal and paternal chromatin and penetrating microtubules in human oocytes failing to fertilize after intracytoplasmic sperm injection. Mol Reprod Dev 55,197–204.[CrossRef][Web of Science][Medline]
Kubiak JZ (1989) Mouse oocytes gradually develop the capacity for activation during the metaphase II arrest. Dev Biol 136,537–545.[CrossRef][Web of Science][Medline]
Liu H, Krey LC, Zhang J and Grifo JA (2001) Ooplasmic influence on nuclear function during the metaphase II–interphase transition in mouse oocytes. Biol Reprod 65,1794–1799.
Liu L, Ju JC and Yang X (1998) Differential inactivation of maturation-promoting factor and mitogen-activated protein kinase following parthenogenetic activation of bovine oocytes. Biol Reprod 59,537–545.
Lopata A and Leung PC (1988) The fertilizability of human oocytes at different stages of meiotic maturation. Ann NY Acad Sci 541,324–356.[CrossRef][Web of Science][Medline]
Lundin K, Ziebe S, Bergh C, Loft A, Wikland M, Nyboe Andersen A, Selleskog U, Grondahl C and Arce J (2002) Aneuploidy rate of human embryos originating from immature oocytes in stimulated cycles [abstract O-234]. Hum Reprod (Abstact Book) 17,81.
Masui Y (1992) Towards understanding the control of the division cycle in animal cells. Biochem Cell Biol 70,920–945.[Web of Science][Medline]
Moor RM, Dai Y, Lee C and Fulka J Jr (1998) Oocyte maturation and embryonic failure. Hum Reprod Update 4,223–236.
Nogueira D, Staessen C, Van de Velde H and Van Steirteghem A (2000) Nuclear status and cytogenetics of embryos derived from in vitro-matured oocytes. Fertil Steril 74,295–298.[CrossRef][Web of Science][Medline]
Plachot M (1995) Oocyte-genetic aspects. In: Grudzinska JG and Yovich JL (eds), Gametes—The Oocyte. Cambridge University Press, Cambridge, pp. 95–107.
Schultz GA, Grifford DJ, Mahadevan MM, Fleetham JA and Taylor PJ (1988) Protein synthetic patterns in immature and mature human oocytes. Ann NY Acad Sci 541,237–247.[Web of Science][Medline]
Trounson AO, Mohr L, Wood C and Leeton JF (1982) Effect of delayed insemination on in vitro fertilization, culture and transfer of human embryos. J Reprod Fertil 64,285–294.
Trounson A, Anderiesz C and Jones G (2001) Maturation of human oocytes in vitro and their developmental competence. Reproduction 121,51–75.[Abstract]
Verlhac MH, De Pennart H, Maro B, Cobb MH and Clarke HJ (1993) MAP kinase becomes stably activated at metaphase and is associated with microtuble-organizing centres during meiotic maturation of mouse oocyte. Dev Biol 158,330–340.[CrossRef][Web of Science][Medline]
Ware CB, Barnes FL, Maiki-Laurila M and First NL (1989) Age dependence of bovine oocyte activation. Gamete Res 22,265–275.[CrossRef][Web of Science][Medline]
Xu Z, Abbott A, Kopf GS, Schultz M and Ducibella T (1997) Spontaneous activation of ovulated mouse eggs: time-dependent effects on M-phase exit, cortical granule exocytosis, maternal messenger ribonucleic acid recruitment, and inositol 1,4,5-trisphosphate sensitivity. Biol Reprod 57,743–750.[Abstract]
Submitted on August 26, 2003; accepted on January 5, 2004.
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  C. Dupont, B. D. Bavister, D. R. Armant, and C. A. Brenner Rhesus macaque embryos derived from MI oocytes maturing after retrieval display high rates of chromosomal anomalies Hum. Reprod., April 1, 2009; 24(4): 929 - 935. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C.-S. Hyun, J.-H. Cha, W.-Y. Son, S.-H. Yoon, K.-A. Kim, and J.-H. Lim Optimal ICSI timing after the first polar body extrusion in in vitro matured human oocytes Hum. Reprod., July 1, 2007; 22(7): 1991 - 1995. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L. Vanhoutte, P. De Sutter, D. Nogueira, J. Gerris, M. Dhont, and J. Van der Elst Nuclear and cytoplasmic maturation of in vitro matured human oocytes after temporary nuclear arrest by phosphodiesterase 3-inhibitor Hum. Reprod., May 1, 2007; 22(5): 1239 - 1246. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. V. Bokal, H. M. Vrtovec, I. V. Klun, and I. Verdenik Prolonged HCG action affects angiogenic substances and improves follicular maturation, oocyte quality and fertilization competence in patients with polycystic ovarian syndrome Hum. Reprod., June 1, 2005; 20(6): 1562 - 1568. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P.M. Ciotti, L. Notarangelo, A.M. Morselli-Labate, V. Felletti, E. Porcu, and S. Venturoli First polar body morphology before ICSI is not related to embryo quality or pregnancy rate Hum. Reprod., October 1, 2004; 19(10): 2334 - 2339. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||