Oocyte Cleavage Research Articles

Cryopreservation of Mature Bovine Oocytes by Vitrification in Straws

Experiments were conducted to determine optimal conditions for vitrification ofin vitromatured bovine oocytes in straws. In the first series of experiments, the effects of stepwise addition before exposure of oocytes to vitrification solution consisting of 30% (v/v) ethylene glycol (EG) with 0.35 M sucrose was tested. The rates of morphological survival and cleavage of oocytes vitrified by the three-step addition procedure were higher than those vitrified by the one-step addition procedure. In the second series, the effect of the concentration of the vitrification solution was tested (20, 30, 40, and 50% EG, all with 0.35 M sucrose). The survival rates of oocytes vitrified in 20 and 30% EG were lower than those in 40 and 50% EG. The rates of cleavage and development to blastocysts of oocytes vitrified in 40% EG were the highest among the four groups. In the third series, the effect of duration of exposure of oocytes to 0.5 M sucrose (1, 5, and 10 min) at the first step during the three-step dilution was tested. Although there were no significant differences among the groups with respect to developmental competence of oocytes vitrified in 40% EG, the highest development rate (10%) to blastocysts was observed when oocytes were exposed to sucrose for 5 min. These data demonstrate that improvements to the concentration of cryoprotectant and addition procedures have critical effects on the developmental competence of oocytes vitrified in straws.

Activation regimens to prepare bovine oocytes for intracytoplasmic sperm injection.

Activation of bovine oocytes to produce a single haploid pronucleus in preparation for intracytoplasmic sperm injection (ICSI) has been investigated with various combinations of ionomycin and 6-dimethylaminopurine (DMAP). Effects were evaluated by immunocytochemical staining, chromosomal analysis and assessment of development in vitro. Oocytes matured in vitro were exposed to: ionomycin alone (single or repeated treatments, Groups 1 and 2 respectively), ionomycin followed by DMAP (immediately or after a 3-h delay, Groups 3 and 4), or no treatment (control, Group 5). They were then co-cultured in M199 with bovine oviductal epithelial cells. Activation rates were not significantly different among groups but significantly fewer oocytes in Group 3 extruded a second polar body than in Groups 1, 2, and 4. Most parthenotes (60% to 80%) in Groups 1, 2, and 4 were haploid, whereas 82% in Group 3 were mixoploid or polyploid. Most of the parthenotes (88%) in Group 4 formed a single pronucleus besides extruding the second polar body and were therefore more suitable for ICSI than those of Groups 1 and 2 in which condensed chromosomes predominated. The respective rates of oocyte cleavage in Groups 1 to 4 were 24%, 36%, 70%, and 75%; corresponding blastocyst rates were 1%, 5%, 17%, and 8%. There were significantly fewer cells in the parthenotes of Groups 1, 2, and 4 than of Group 3, or of embryos produced by in vitro fertilization. Thus, delaying the addition of DMAP after ionomycin decreases chromosomal abnormalities and produces a high proportion of activated oocytes suitable for ICSI.

Anaesthesia for assisted conception

Anaesthesia for assisted conception

Control of oocyte maturation in cows — Biological factors

Since bovine in vitro fertilization became possible in the early 80s, a lot of effort has been done to clarify the mechanisms of what seems more and more one of the crucial steps in this procedure, being oocyte maturation. Undoubtedly, many biological factors act together to prepare the immature oocyte for a successful development to a competent embryo after fertilization. Defects in oocyte maturation can possibly be caused by an inadequate nuclear or cytoplasmic maturation or even by a failure of both. There is a general agreement upon the fact that the origin of the oocyte can play an important role. Oocytes derived from very small follicles show a lower rate of maturation and lower blastocyst development with currently used maturation protocols. Parthenogenetic activation of small size follicle derived oocytes suggests that their poor development was not caused by fertilization problems but more likely by intrinsic oocyte factors. Similar developmental rates achieved through nuclear transfer and parthenogenetic activation suggests that the nucleus of the incompetent oocyte may not be the sole reason for a poor development. Another important factor appears to be the donor animal age. The younger the donor animal, the more impaired is its oocyte's developmental competence in most of the embryo IVP systems. Treatment with exogeneous gonadotropins can be beneficial in young donors on the oocyte cleavage rates but does not always increase the final blastocyst outcome. This review briefly documents some of the biological factors and their possible effects on the developmental capacities of the bovine oocyte in vitro.

O-030. Fertilization, cleavage and pregnancy rates of oocytes from large and small follicles

O-030. Fertilization, cleavage and pregnancy rates of oocytes from large and small follicles

Effects of 1,2-propanediol and freezing-thawing on the in vitro developmental capacity of human immature oocytes

To investigate effects of 1,2-propanediol and freezing-thawing treatment on the maturation and developmental capacity of the human immature oocytes obtained from unstimulated ovaries. Intact cumulus-enclosed immature oocytes collected from unstimulated ovaries were divided into three groups, such as no treatment as control (group 1), only 1,2-propanediol-treated (group 2), and cryopreserved group (group 3). Oocytes in group 1, group 2, and survived oocytes from cryopreservation in group 3 were cultured for 48 hours. A random selection of matured oocytes was inseminated with normal donor sperm to evaluate the fertilization and developmental capacity. Infertility Medical Center at the CHA General Hospital, Seoul, Korea. Oocytes were obtained from patients undergoing gynecological surgery. Rates of survival, maturation to metaphase II, fertilization, and cleavage. Survival rate after freezing-thawing in group 3 was 55.1% (54/98). Oocytes were cultured in Dulbecco's modified Eagle's medium (DMEM) supplemented with 20% fetal bovine serum, 10 IU/mL pregnant mare serum gonadotropin, and 10 IU/mL hCG. Maturation rates were 76.8% (63/82), 67.1% (47/70), and 59.3% (32/54) in the groups 1, 2, and 3, respectively. Maturation rate in group 3 was significantly lower than that of group 1. Fertilization rates were 90.5% (19/21), 81.0% (17/21), and 42.9% (6/14), and cleavage rates were 94.7% (18/19), 88.2% (15/17), and 16.7% (1/6) in groups 1, 2, and 3, respectively. Fertilization and cleavage rates of survived oocytes in group 3 also were significantly lower than those of groups 1 and 2. Results suggest that the pretreatment with 1.5 M 1,2-propanediol itself before the freezing has no inhibitory effect on the maturation, fertilization, and cleavage of human immature oocytes in vitro. However, the freezing-thawing procedure used had detrimental effects on the maturation and developmental capacity.

Functional enucleation of bovine oocytes: Effects of centrifugation and ultraviolet light

Functional enucleation is removal or denaturation of an oocytes DNA without piercing the zona pellucida. Two experiments were conducted in this study to determine the effects of centrifugation, and ultraviolet (UV) light on metaphase II bovine oocytes. Experiment 1 evaluated the effects of centrifugation (12,000 × g for 4 min) on the cleavage rate of in vitro matured oocytes. Centrifugation decreased (P < 0.05) the cleavage rate of oocytes (79.5 vs 70.4 %). In addition, it was noted that there were two types of ooplasm after centrifugation, stratified and granular. Developmental potential, as represented by cleavage percent, of the two types of ooplasm was not significantly different. Experiment 2 was conducted to determine the interactive effects of centrifugation (as above) and UV light (254 nm) on cleavage rate of oocytes exposed as metaphase II oocytes. The UV light decreased (P < 0.07) oocyte cleavage rates (35.4 vs 25.2 %). Centrifuging metaphase II oocytes also decreased (P < 0.07) cleavage rates (34.1 vs 26.5 %). In addition, we determined the fate of chromosomes of oocytes centrifuged and(or) exposed to UV light. Both centrifugation and UV light alone affected (P < 0.05) chromosome placement at 42 ± 3 h after fertilization. Furthermore, centrifugation and UV light interactively increased (P < 0.05) the percentage of non-cleaved oocytes with their DNA located in the perivitelline space (17.4, 15.5, 13.1, and 49.2, respectively, for control, UV exposed, centrifuged, and UV∗centrifuged). Collectively, these data indicate that bovine oocytes at the metaphase II stage can be functionally enucleated with centrifugation and exposure to UV light; however, developmental potential may be diminished by those techniques.

Delayed cleavage of human oocytes after intracytoplasmic sperm injection

Delayed cleavage of human oocytes after intracytoplasmic sperm injection

The Effect of Salinity and Temperature on Spawning and Fertilization in the Zebra Mussel Dreissena polymorpha (Pallas) from North America.

Zebra mussels have dispersed from their original site of introduction in the Great Lakes into the Mississippi River, Hudson River, and other watersheds in which they will encroach upon brackish water estuaries. To investigate their likelihood of reproductive success in such estuaries, we investigated the conditions of temperature, salinity, and acclimation under which spawning and fertilization could occur. Reproductive function of mussels that were acclimated to salinities up to 7.0 parts per thousand (ppt) at 12°, 20°, and 27°C for 1 to 21 days was tested. Reproductive function of non-acclimated mussels that had been maintained in fresh-water aquaria was also tested in various salinities. Spawning was induced by serotonin, previously demonstrated to elicit spawning of fertile gametes in fresh water. Successful fertilization was indicated by oocyte cleavage after adding sperm. Nonacclimated mussels spawned in salinities of 1.75 and 3.5 ppt at 12°, 20°, and 27°C, but not at 7.0 ppt. Fertilization using gametes from non-acclimated mussels occurred only in fresh water and at 1.75 ppt. Acclimation for as little as 2 days enhanced spawning. Fertilization rate in a salinity of 3.5 ppt improved within 4 days of acclimation and continued at a high level for as long as 21 days of acclimation. Although animals acclimated for 4 days in 3.5 ppt spawned readily when tested in salinities as high as 7.0 ppt, almost no fertilization occurred in 7.0 ppt. The reduction in fertilization at increasing salinities may be due in part to reduced sperm motility. Unfertilized oocytes remain intact for hours in fresh water; however, in salinities as low as 0.7 ppt, unfertilized oocytes tended to rupture within 2 hours. These data show that although sudden increases in salinity produce an immediate decrease in the reproductive capacity of zebra mussels, acclimation to brackish water can occur, and zebra mussels may be able to reproduce in brackish water below 7.0 ppt.

Experimental extension of the time interval between oocyte maturation and ovulation: effect on fertilization first cleavage

To test the hypothesis that impaired fertility in human patients with high LH concentrations throughout the follicular phase of the menstrual cycle reflects premature maturation of their oocytes. Previous information that resumption of meiosis is induced by lower hCG concentrations than that required for stimulation of follicular rupture was confirmed and used for establishment of a rat animal model in which oocyte maturation and ovulation can be separated experimentally. In further experiments hypophysectomized, pregnant mare serum gonadotropin (PMSG)-primed, immature female rats injected with 1.1 IU of hCG, a dose found to induce maturation in 72.9% +/- 6% of the rats with no effect on ovulation, were administered with a second injection of an ovulatory dose (4 IU) of hCG, 24 hours later. The ovulated eggs were subjected to IVF. Fertilization and first cleavage in oocytes recovered from our experimental animal model were similar to that observed in control PMSG-primed, either hypophysectomized or intact rats, treated by a single injection of 4 IU of hCG. The extension of the time interval between oocyte maturation and ovulation in the rat does not result in a lower rate of fertilization or a reduced incidence of cleavage. However, an inferior developmental capacity of these embryos cannot be ruled out.

The first successful transfer of frozen embryos derived from IVMFC of bovine oocytes in hungary

The present study aimed to determine if there is bull to bull variation in the binding of the anti-human sperm monoclonal antibody (MAb) HS-11 to bull spermatozoa, and to investigate if there is any correlation between HS-11 binding to spermatozoa and in vitro fertility of the bulls tested. Semen samples of a single collection (split frozen in 0.5-ml straws) from 8 dairy bulls were used. Swim-up separated motile spermatozoa were incubated in 90-μ1 drops of capacitation medium (TALP+10 μg/ml heparin) at 39 °C, 5% CO2, 95% air. At 0, 2, 4 and 6 h of incubation HS-11 was added (1:1000 final concentration), and the MAb binding was assessed by indirect immunofluorescence assay (IIFA). The HS-11 binding was indicated by a bright green fluorescence of the sperm acrosome region. In vitro-matured, good quality bovine oocytes were randomly allocated to spermatozoa of each bull for in vitro fertilization. Sperm samples of 2 to 3 bulls were used in each trial until 4 replicates per bull were attained for IVF (n ≈ 100 oocytes/bull) and IIFA experiments. Sperm capacitation status was assessed simultaneously using an egg yolk lysophosphatidylcholine- (LC) induced acrosome reaction assay. The binding of HS-11 to spermatozoa was maximum at 4 h of incubation in most (68) of the bull semen samples. Significant (P < 0.01) differences were observed between bulls in the binding of HS-11 to their spermatozoa (range 22 ± 8 to 52 ± 5%) at 4 h, but not within replicates. Similarly, variations (P < 0.05) in the cleavage rate were also seen (range 22 ± 9 to 58 ± 7%) between bulls. The HS-11 binding and cleavage were significantly correlated (r = 0.43; n = 32; P < 0.05). The highest percentage of spermatozoa underwent acrosome reaction in response to LC treatment at the 4-h incubation period. This and the linear relationship between HS-11 binding and the cleavage rate observed in the present study together strengthen our earlier suggestion that the binding of the monoclonal antibody HS-11 to bull spermatozoa on a time-dependent manner, may indicate capacitation changes. We conclude that 1) between-bull differences exist in HS-11 binding to spermatozoa, and in the cleavage rate, and 2) HS-11 binding to spermatozoa is correlated with fertility, as determined by the cleavage of bovine oocytes matured and fertilized in vitro.

Binding of the anti-human sperm monoclonal antibody HS-11 to bull spermatozoa is correlated with fertility in vitro

The present study aimed to determine if there is bull to bull variation in the binding of the anti-human sperm monoclonal antibody (MAb) HS-11 to bull spermatozoa, and to investigate if there is any correlation between HS-11 binding to spermatozoa and in vitro fertility of the bulls tested. Semen samples of a single collection (split frozen in 0.5-ml straws) from 8 dairy bulls were used. Swim-up separated motile spermatozoa were incubated in 90-μ1 drops of capacitation medium (TALP+10 μg/ml heparin) at 39 °C, 5% CO 2, 95% air. At 0, 2, 4 and 6 h of incubation HS-11 was added (1:1000 final concentration), and the MAb binding was assessed by indirect immunofluorescence assay (IIFA). The HS-11 binding was indicated by a bright green fluorescence of the sperm acrosome region. In vitro-matured, good quality bovine oocytes were randomly allocated to spermatozoa of each bull for in vitro fertilization. Sperm samples of 2 to 3 bulls were used in each trial until 4 replicates per bull were attained for IVF (n ≈ 100 oocytes/bull) and IIFA experiments. Sperm capacitation status was assessed simultaneously using an egg yolk lysophosphatidylcholine- (LC) induced acrosome reaction assay. The binding of HS-11 to spermatozoa was maximum at 4 h of incubation in most ( 6 8 ) of the bull semen samples. Significant (P < 0.01) differences were observed between bulls in the binding of HS-11 to their spermatozoa (range 22 ± 8 to 52 ± 5%) at 4 h, but not within replicates. Similarly, variations (P < 0.05) in the cleavage rate were also seen (range 22 ± 9 to 58 ± 7%) between bulls. The HS-11 binding and cleavage were significantly correlated (r = 0.43; n = 32; P < 0.05). The highest percentage of spermatozoa underwent acrosome reaction in response to LC treatment at the 4-h incubation period. This and the linear relationship between HS-11 binding and the cleavage rate observed in the present study together strengthen our earlier suggestion that the binding of the monoclonal antibody HS-11 to bull spermatozoa on a time-dependent manner, may indicate capacitation changes. We conclude that 1) between-bull differences exist in HS-11 binding to spermatozoa, and in the cleavage rate, and 2) HS-11 binding to spermatozoa is correlated with fertility, as determined by the cleavage of bovine oocytes matured and fertilized in vitro.

Pregnancy: Intrafollicular concentrations of free cortisol close to follicular rupture

Concentrations of total and free, non-protein-bound cortisol were determined in serum and pre-ovulatory follicular fluid sampled from 14 women who underwent in-vitro fertilization (IVF) embryo transfer treatment. Seven of the women became pregnant and seven did not. In the pregnant group the number of pre-embryos transferred was equal to the number of implantations, identifying the follicles which contained an oocyte that resulted in a clinical pregnancy after IVF. The concentrations of free and total cortisol in follicular fluid were associated with oocyte cleavage and the establishment of pregnancies. Follicular fluid concentrations of total cortisol averaged 78% of that found in serum (244 versus 312 nM), whereas the concentration of free biologically active cortisol was nearly 10 times higher in follicular fluid than in serum (54 versus 6 nM). In serum > 94% of the cortisol was bound to cortisol binding protein (CBP) and 2.1% was free. In contrast, follicular fluid contained 22% free cortisol and only 48% bound to CBP. Follicles associated with pregnancy contained similar amounts of both free and total cortisol compared with follicles in which the oocyte failed to implant or did not cleave in vitro. It is suggested that the high concentrations of free cortisol in pre-ovulatory follicular fluid may confine and reduce some of the inflammatory-like reactions which take place close to follicular rupture. This study does not support the current concept of cortisol playing a role in follicular development of large antral follicles and oocyte maturation during the follicular phase.

Time-course of oocyte activation, pronucleus formation and cleavage in human oocytes fertilized by intracytoplasmic sperm injection.

Knowledge of the timing of the stages of fertilization in humans is still limited because the time of gamete fusion is not known when pre-ovulatory or in-vitro matured cumulus-enclosed oocytes are inseminated. We therefore studied the morphological nuclear changes in 14 patients' oocytes by means of light microscopic observation at 2, 4, 6, 8, 16, 18 and at 20 h after intracytoplasmic single sperm injection (ICSI). A total of 144 metaphase II oocytes were injected with the spermatozoa of the patients' partners. Out of the 134 oocytes that survived the injection, 93 displayed two pronuclei in the course of the observation period (69%). Out of the 93 normally fertilized oocytes, 21 extruded the second polar body at 2 h after micro-injection (23%) and 63 oocytes at 4 h (68%). Pronuclei appeared as early as 6 h after ICSI in 16 normally fertilized oocytes (17%). At 8 h, 75 (80%) oocytes had two visible pronuclei, at 16 h 92 (99%), at 18 h 76 (82%) and at 20 h 63 (68%). In 24 oocytes (26%) the appearance of pronuclei was asynchronous, while the disappearance of the pronuclei was always synchronous, except in one oocyte. Nine of the 134 successfully injected oocytes showed three equal-sized pronuclei (6.7%). Four of the nine multi-pronucleated oocytes did not extrude the second polar body at all, while the time sequence of appearance of pronuclei was similar to that of the normally fertilized oocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of IGF‐I on pig oocyte maturation, fertilization, and early embryonic development in vitro, and on granulosa and cumulus cell biosynthetic activity

Porcine granulosa cells have been shown previously to both secrete and respond to insulin-like growth factor-I (IGF-I), suggesting an autocrine function of this peptide in the follicle. The present work was undertaken to determine possible effects of IGF-I on in vitro maturation, in vitro fertilization, and early embryonic development in culture. Granulosa and cumulus cell proliferation and differentiation based on 3H-thymidine uptake and progesterone production, respectively, were also assessed. The results showed that the cleavage rate of oocytes was markedly stimulated in a dose-dependent manner by the addition of IGF-I to the oocyte maturation medium (P < 0.05). Embryo development beyond the 8-cell stage was improved by IGF-I, reaching a maximum of 22% at 200 ng/ml IGF-I. Treatment with IGF-I after fertilization increased the percentage of total oocyte cleavage (P < 0.05) to approximately 52%, 43%, and 57% at, respectively, 25, 50, and 100 ng/ml IGF-I. 3H-thymidine incorporation by granulosa cells was significantly increased in cultures treated with FSH (3-fold) or IGF-I (6-fold) compared to the control. For the cumulus cells, FSH caused a similar increase (3-fold) in 3H-thymidine incorporation while IGF-I stimulated a 15-fold increase. Progesterone production by the granulosa cells was increased to the same extent by treatment with FSH or IGF-I (4.7 and 5.1-fold, respectively). However, for the cumulus cells, while FSH caused a marked 16-fold increase in progesterone production, IGF-I caused only a marginal increase of 2.5-fold.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro maturation, fertilisation and culture of bovine oocytes in a modified Ménézo B2 medium

In this study we investigated the influence of essential amino acid composition of the medium on in vitro maturation and culture of bovine oocytes (cleavage of oocytes and development capacity of embryos). Oocytes were matured and cultured in vitro in a modified Ménézo B2 medium (MMM). The medium was modified by adding amino acids, not as single compounds, but as amino acid supplements for MEM (Minimum Essential Medium) or BME (Basal Medium Eagle) tissue culture medium, which differ completely in their content of essential amino acids. In the medium with MEM supplements the content of all essential amino acids except glutamine is at least twice as high as in the BME-supplemented medium. Oocytes were randomly allocated to one of four treatments: (1) in vitro maturation (IVM) and in vitro culture (IVC) in MMM with MEM amino acids (MEM medium); (2) IVM in MEM medium, IVC in MMM with BME supplements (BME medium); (3) IVM in BME medium, IVC in MEM medium; (4) IVM and IVC in BME medium. After IVM in MEM medium, more cumulus-oocyte complexes displayed marked expansion of the cumulus cells and cleavage occurred more frequently than after IVM in BME medium. More oocytes underwent cleavage when cultured in MEM medium than in BME medium. A higher number of embryos entered the compact morula or blastocyst stage when cultured in BME medium. Development to the blastocyst stage occurred faster after IVM and IVC in BME medium than in the other groups. The results demonstrate that the content of essential amino acids of the maturation and culture medium affects the development of bovine embryos in vitro.

Addition of penicillamine, hypotaurine and epinephrine (PHE) or bovine oviductal epithelial cells (BOEC) alone or in combination to bovine in vitro fertilization medium increases the subsequent embryo cleavage rate

The cleavage rate of in vitro-matured bovine oocytes was compared after fertilization in 1) TALP medium alone (control); 2) in TALP + BOEC; 3) in TALP + PHE; or 4) in TALP + BOEC and PHE. The overall cleavage rate at 45 h post insemination was greater for embryos in Treatments 2 (52%), 3 (55%) and 4 (66%) than for Treatment 1 (32%). The oocyte cleavage rates for Treatments 2 and 3 were similar, but were lower than that of Treatment 4. Addition of PHE or BOEC, alone or in combination, to the fertilization medium resulted in more embryos at the 3- or 4-cell stage than the 2-cell stage by 45 h post insemination. After 5 d of co-culture with BOEC in M-199 medium, 21, 28, 25 and 35% of the cleaved embryos in Treatments 1, 2, 3 and 4, respectively, developed to the morula or blastocyst stage. The rate of development to morulae and blastocysts was similar among Treatments 1, 2 and 3, and between Treatments 2 and 4. Across treatments, a correlation of 0.98 was noted between the portion of embryos that had reached the 3- or 4-cell stage by 45 h post insemination and the percentage of embryos in each treatment that continued to develop to the morula or blastocyst stage in vitro.

Experimental Production of Triploid Bovine Embryos by Microinjection of Two Sperm and Their Development.

To clarify the effect of triploidy on the development of bovine embryos, one or 2 sperm were injected into mature bovine oocytes and subsequent development and chromosome composi-tion were investigated. The cleavage rates of oocytes injected with one or 2 sperm using oocytes matured in vitro for 24 h were 36.3% (69/190) and 39.0% (53/136), respectively. Most of the embryos injected with 2 sperm had arrested development before the 8-cell stage and none devel-oped to the morula stage, although three (1.6%) embryos injected with one sperm developed to the blastocyst stage. The incidence of triploid embryos derived from 2-sperm injection was 12.9%, and the incidences of diploid and haploid embryos were 48.4% and 12.9%, respectively. About half (44.9%) of the uncleaved oocytes injected with one sperm and one-third (32.1%) of those injected with 2 sperm stopped developing at the second anaphase just after activation by ionophore treat-ment. Three pronuclei (10.7%) and one-cell metaphase (28.6%) with chromosome sets spread in 3 directions were observed only in uncleaved oocytes after 2-sperm injection. These facts suggested that triploidy is not the sole cause of arrested development before the 8-cell stage in cleaved embryos, although 2-sperm penetration and pronuclei formation strongly influenced oocyte cleav-age.

A nuclear factor required for specific translation of cyclin B may control the timing of first meiotic cleavage in starfish oocytes.

In most animals, the rate of cyclin B synthesis increases after nuclear envelope breakdown during the first meiotic cell cycle. We have found that cyclin B-cdc2 kinase activity drops earlier in emetine-treated than in control starfish oocytes, although the protein synthesis inhibitor does not activate the cyclin degradation pathway prematurely. Moreover, protein synthesis is required to prevent meiotic cleavage to occur prematurely, sometimes before chromosomes have segregated on the metaphase plate. In normal conditions, increased synthesis of cyclin B after germinal vesicle breakdown (GVBD) balances cyclin degradation and increases the time required for cyclin B-cdc2 kinase to drop below the level that inhibits cleavage. Taken together, these results point to cyclin B as a possible candidate that could explain the need for increased protein synthesis during meiosis I. Although direct experimental evidence was not provided in the present work, cyclin B synthesis after GVBD may be important for correct segregation of homologous chromosomes at the end of first meiotic metaphase, as shown by a variety of cytological disorders that accompany premature cleavage. Although the overall stimulation of protein synthesis because of cdc2 kinase activation is still observed in oocytes from which the germinal vesicle has been removed before hormonal stimulation, the main increase of cyclin B synthesis normally observed after germinal vesicle breakdown is suppressed. The nuclear factor required for specific translation of cyclin B after GVBD is not cyclin B mRNA, as shown by using a highly sensitive reverse transcription followed by polymerase chain reaction procedure that failed to detect any cyclin B mRNA in isolated germinal vesicles.

Premature elevation of plasma progesterone alters pregnancy rates of in vitro fertilization and embryo transfer

To determine if an increase in plasma P occurring before hCG administration might impair the outcome of IVF-ET. Five hundred eighty-five IVF-ET cycles were prospectively studied for the occurrence of plasma P elevation before hCG administration. Tertiary institution, IVF-ET program, Hôpital A. Béclère. Participating patients included IVF-ET candidates 23 to 42 years of age only, excluding the couples in whom a male factor was a primary or an accessory cause of infertility. To clarify the practical consequences on IVF-ET outcome of pre-hCG increases in plasma P, we studied 585 consecutive IVF-ET cycles. These were divided into two groups according to plasma P levels observed on the day of hCG administration; plasma P of 0.9 ng/mL (2.9 nmol/L) was taken as an arbitrary cutoff value. Group A included 485 IVF cycles in which plasma P was < or = 0.9 ng/mL (2.9 nmol/L); group B included the remaining 100 cycles in which plasma P was > 0.9 ng/mL (2.9 nmol/L). The number of mature oocytes retrieved, the oocyte cleavage rate, and the number of embryos obtained were similar in groups A and B. In contrast to this apparent similarity in oocyte quality, a decrease in pregnancy rate (PR) and a trend for a decrease in embryo implantation rate were observed in group B in comparison with group A. The similar fertilization and cleavage rates obtained in groups A and B suggest that pre-hCG elevation in plasma P does not lead to decreased oocyte quality. Yet the lower PR observed when plasma P rises prematurely suggests that the prolonged but discrete elevation in plasma P occurring in these cases might alter endometrium receptivity to embryo implantation.