Effects of maternal age on oocyte developmental competence

Is later better or worse? Association of advanced parental age with offspring cognitive ability among half a million young Swedish men

Parental ages are increasing in the developed world, and postponed parenthood may have a negative association with the cognitive ability of offspring. There is, however, inconclusive evidence regarding the impact of both maternal and paternal ages. We have been able to reduce or eliminate unobserved confounding by using methods that account for fixed parental characteristics shared by brothers. Associations between parental age and intelligence quotient (IQ) among 565,433 Swedish males (birth cohorts 1951 to 1976) were analyzed, with IQ measured at conscription examinations (given between ages 17 and 20 years). When we accounted for the IQ time trend by adjusting for birth year, advanced paternal age showed no association with offspring IQ; however, maternal ages above 30 years were inversely associated with offspring IQ. For example, maternal ages 40-44 years were associated with an offspring IQ that was 0.07 standard deviations lower than that for maternal ages 25-29 years (P < 0.001). However, the IQ trend more than offset the impact of age, as without birth year adjustment, advanced maternal age was positively associated with IQ. Although the results confirmed that maternal age was negatively associated with offspring IQ, the association was small enough that delaying parenthood resulted in higher offspring IQ scores because of the positive IQ test score trend.

Maternal age and offspring adult health: evidence from the health and retirement study

Advanced maternal age is associated with negative offspring health outcomes. This interpretation often relies on physiological processes related to aging, such as decreasing oocyte quality. We use a large, population-based sample of American adults to analyze how selection and lifespan overlap between generations influence the maternal age-offspring adult health association. We find that offspring born to mothers younger than age 25 or older than 35 have worse outcomes with respect to mortality, self-rated health, height, obesity, and the number of diagnosed conditions than those born to mothers aged 25-34. Controls for maternal education and age at which the child lost the mother eliminate the effect for advanced maternal age up to age 45. The association between young maternal age and negative offspring outcomes is robust to these controls. Our findings suggest that the advanced maternal age-offspring adult health association reflects selection and factors related to lifespan overlap. These may include shared frailty or parental investment but are not directly related to the physiological health of the mother during conception, fetal development, or birth. The results for young maternal age add to the evidence suggesting that children born to young mothers might be better off if the parents waited a few years.

Methyl donor supplementation of gestating sow diets improves pregnancy outcomes and litter size

Maternal intake of B-vitamin and methyl donors can affect sow prolificacy. A total of 1079 Large White/Landrace sows (parities 2–9 at mating) were used in a 2 by 2 by 2 factorial design to determine the effects of two levels of betaine supplementation (0 versus 3 g added betaine/kg feed), two levels of folic acid plus vitamin B12 supplementation (0 versus 20 mg/kg folic acid plus 150 µg/kg vitamin B12) during gestation, and two parity groups (parity 2 and 3 versus parity 4 and greater) on litter size and pregnancy outcomes. The number of sows returning to oestrus post-insemination, as well as the number of early (<Day 30) and late (>Day 30) pregnancy losses were recorded. At farrowing, the total number of piglets born, the number of piglets born alive and dead, as well as the number of mummified fetuses were recorded. Pre-prandial blood samples were collected from a subset of 20 sows/treatment on Days 3, 30 and 107 of gestation to analyse homocysteine. The incidence of early pregnancy loss was reduced (P < 0.001) by folic acid plus vitamin B12 supplementation (0.03 versus 0.07). There was a significant interaction between parity at mating (parities 2 and 3 versus parity 4 and greater) and the addition of betaine or folic acid plus vitamin B12 to the gestation diet on litter size. Litter size was higher (0.5 piglets; P < 0.05) for betaine supplemented, compared with unsupplemented, parity 4 plus sows. Folic acid plus vitamin B12-supplemented parity 2 and 3 sows gave birth to more (P < 0.05) piglets than all other treatment groups. Folic acid plus vitamin B12 supplementation decreased (P < 0.001) plasma homocysteine concentration by 2.2 and 2.8 μM, respectively, on Days 3 and 107 of gestation. However, betaine supplementation decreased (P < 0.05) homocysteine on Day 3 only. Overall, folic acid plus vitamin B12 supplementation decreased incidences of early pregnancy failure and increased litter size in early parity sows, while betaine increased litter size in older parity sows.

Functional analysis of lysosomes during mouse preimplantation embryo development

Lysosomes are acidic and highly dynamic organelles that are essential for macromolecule degradation and many other cellular functions. However, little is known about lysosomal function during early embryogenesis. Here, we found that the number of lysosomes increased after fertilization. Lysosomes were abundant during mouse preimplantation development until the morula stage, but their numbers decreased slightly in blastocysts. Consistently, the protein expression level of mature cathepsins B and D was high from the one-cell to morula stages but low in the blastocyst stage. One-cell embryos injected with siRNAs targeted to both lysosome-associated membrane protein 1 and 2 (LAMP1 and LAMP2) were developmentally arrested at the two-cell stage. Pharmacological inhibition of lysosomes also caused developmental retardation, resulting in accumulation of lipofuscin. Our findings highlight the functional changes in lysosomes in mouse preimplantation embryos.

Noninvasive imaging of the meiotic spindle of in vivo matured oocytes from infertile women with endometriosis

The objectives of this prospective study were to evaluate the nuclear maturation stage and the presence and location of meiotic spindles of in vivo matured oocytes from infertile women with and without endometriosis (male or tubal causes of infertility) undergoing stimulated cycles for intracytoplasmic sperm injection (ICSI). We also compared the ICSI outcomes among groups. We analyzed the meiotic spindles of oocytes from 36 patients with endometriosis I/II, 24 with endometriosis III/IV, and 60 without endometriosis (male or tubal causes of infertility). The oocytes were imaged using polarization microscopy. There were no differences in the number of oocytes in telophase I (mean [standard deviation]: 0.1 [0.5], 0.2 [0.4], and 0.2 [0.5], respectively, in the endometriosis I/II, endometriosis III/IV, and control groups), in metaphase II with visible spindles (4.2 [2.5], 3.1 [2.0], and 3.6 [2.2], respectively, in the endometriosis I/II, endometriosis III/IV, and control groups), and in spindle location among groups. We can conclude from this study that noninvasive analysis of spindles from in vivo matured oocytes of infertile patients with endometriosis did not demonstrate significant differences in terms of the nuclear maturation stage, the percentage of oocytes in metaphase II with visible spindles, and the spindle localization when compared to the control group. However, it is important to state that there are no studies evaluating the accuracy of polarization microscopy for the detection of meiotic anomalies in human oocytes, which would need to be better evaluated in future studies using an appropriate methodology.

Developmental competence and embryo quality of small oocytes from pre-pubertal goats cultured in IVM medium supplemented with low level of hormones, insulin-transferrin-selenium and ascorbic acid

The aim of this study was to test the effect of insulin-transferrin-selenium (ITS) and L-ascorbic acid (AA) supplementation and the hormonal level during in vitro maturation (IVM) of small oocytes from pre-pubertal goat on the blastocyst yield and quality. Concretely, we used four maturation media: conventional IVM medium (CM), growth medium (GM: CM+ITS+AA and low level of hormones), modified CM (mCM: CM with low level of hormones) and modified GM (mGM: CM+ITS+AA and normal level of hormones). Cumulus-oocyte complexes (COCs) were classified into two categories according to oocyte diameter: <125 μm and ≥ 125 μm. Large oocytes were matured 24 h in CM (Treatment A). Small oocytes were matured randomly in six experimental groups: Treatment B: 24 h in CM; Treatment C: 12 h in GM and 12 h in CM; Treatment D: 24 h in mGM; Treatment E: 12 h in mGM and 12 h in CM; Treatment F: 12 h in mCM and 12 h in CM; and Treatment G: 12 h in GM and 12 h in mGM. After IVM, oocytes were fertilized and cultured for 8 days. The blastocyst quality was assessed by the survival following vitrification/warming and the mean cell number. When different maturation media were combined, the blastocyst rate did not improve. The large oocytes produced the highest blastocysts yield. However, the culture of small oocytes in GM (53.3%) enhanced the post-warming survival of blastocysts compared to large oocytes matured in CM (35.7%). In conclusion, IVM of pre-pubertal goat small oocytes in GM would be useful to improve the quality of in vitro-produced blastocysts.

Gene expression profile differences in embryos derived from prepubertal and adult Japanese Black cattle during in vitro development

The present study was carried out to compare the gene expression profiles of in vitro-generated embryos derived from adult and prepubertal Japanese Black cattle oocytes using GeneChip Bovine Genome Array (containing 24072 probe sets representing over 23000 transcripts). Microarray experiments were performed on populations of 8- to 16-cell stage embryos and blastocysts derived from adult (24-35 months old) versus prepubertal (9-10 months old) Japanese Black cattle oocytes matured and fertilised in vitro. In total, 591 (2.4%) and 490 (2.0%) genes were differentially expressed in prepubertal and adult bovine in 8- to 16-cell and blastocyst stage embryos, respectively. Out of these, 218 and 248 genes were upregulated, while 373 and 242 were downregulated in prepubertal and adult 8- to 16-cell and blastocysts stage embryos, respectively. Gene ontology classification regarding biological process, molecular functions and cellular component revealed diversity in transcript abundances between prepubertal and adult groups in both the distinct developmental stages. Quantitative reverse transcription-PCR validated the expression differences of some selected transcripts as identified by microarray analysis. To our knowledge, this is the first report indicating the significant number of genes differentially expression (>2-fold, P<0.01) in preimplantition embryos between adult and prepubertal Japanese Black cattle during in vitro development.

Age-associated alteration of oocyte-specific gene expression in polar bodies: potential markers of oocyte competence

OBJECTIVE

To confirm that oocyte-specific messenger RNAs are detectable in the polar body (PB) of metaphase II (MII) oocytes and determine the effect of age on oocyte-specific transcript levels.

DESIGN

Prospective study.

SETTING

Hospital-based academic research laboratory.

ANIMAL(S)

CD1 female mice.

INTERVENTION(S)

Aged (40-50 weeks) and young (7-9 weeks) mice were administered pregnant mare serum gonadotropin (PMSG) and hCG. Oocytes were fertilized in vitro to assess fertilization and developmental competence. The MII oocytes were obtained and first PBs were removed. Messenger RNAs from each PB and its sibling oocyte were reverse transcribed and analyzed by real-time quantitative polymerase chain reaction (PCR).

MAIN OUTCOME MEASURE(S)

Fertilization and developmental rates and expression of six oocyte-specific genes (Bmp15, Gdf9, H1foo, Nlrp5, Tcl1, and Zp3) in PBs and sibling oocytes from young versus aged mice.

RESULT(S)

Oocytes from aged mice had lower developmental competence. Four genes (H1foo, Nlrp5, Tcl1, and Zp3) were differentially expressed in aged versus young oocytes. All six transcripts were present in PBs from aged and young mice at lower levels than in the sibling oocytes; transcript levels were lower in aged PBs compared with young PBs.

CONCLUSION(S)

There is a significant difference in the transcript levels of oocyte-specific genes in aged versus young PB that correlates with age-related decreases in oocyte competence. Differences in gene expression in PB may be potential biomarkers of MII oocyte competence.

Abnormal DNA methylation in oocytes could be associated with a decrease in reproductive potential in old mice

PURPOSE

This study was designed to evaluate DNA methylation and the expression of DNA methyltransferases (Dnmt1, Dnmt3a, Dnmt3b and Dnmt3L) in metaphaseII (MII) oocytes and the DNA methylation of pre-implantation embryos during mouse aging to address whether such aging-related changes are associated with decreased reproductive potential in aged mice.

METHODS

Oocytes (MII) from 6 to 8 weeks old female mice are referred to as the 'young group'; oocytes from the same group that were maintained until 35-40 weeks old are referred to as the 'old group.' The oocytes were fertilized both in vitro and in vivo to obtain embryos. The DNA methylation levels in the oocytes (MII) and pre-implantation embryos were assessed using fluorescence staining. The expression levels of the Dnmt genes in the oocytes (MII) were assessed using Western blotting.

RESULTS

The DNA methylation levels in the oocytes and pre-implantation embryos (in vivo and in vitro) decreased significantly during the aging of the mice. The expression levels of all of the examined Dnmt proteins in the old group were lower than young group. Both the cleavage and blastocyst rate were significantly lower in the oocytes of the older mice (69.9 % vs. 80.9 %, P < 0.05; 33.9 % vs. 56.4 %, P < 0.05). The pregnancy rate of the old mice was lower than that of the young mice (46.7 % vs. 100 %, P < 0.05). The stillbirth and fetal malformation rate was significantly higher in the old group than in the young group (17.2 % vs. 2.9 %, P < 0.05).

CONCLUSIONS

The decreased expression of Dnmt1, Dnmt3a, Dnmt3b and Dnmt3L in oocytes (MII) and the change of genome-wide DNA methylation in oocytes and pre-implantation embryos due to aging may be related to lower reproductive potential in old female mice.

Characteristics of bovine oocytes with different meiotic competence in terms of their mitochondrial status and expression of nuclear-encoded factors

The present study was designed to characterize bovine oocytes with different meiotic competence and atresia levels in terms of their mitochondrial status. Oocyte subpopulations were recovered either from medium (MF) or small (SF) follicles and categorized as healthy, light-atretic and mid-atretic according to oocyte morphology. Mitochondrial activity, morphology and distribution, adenosine triphosphate (ATP) content and expression of mitochondrial transcription factor A (TFAM) and nuclear respiratory factor 1 (NRF1) were assessed before (GV) and after (MII) maturation. The data were related to follicular size regardless of or with regard to oocyte atresia. Regardless of atresia, the MF subpopulation showed a significantly higher mitochondrial activity and frequency of oocytes with granulated mitochondria at GV and clustered mitochondria at MII than the SF subpopulation. With regard to atresia, mitochondrial activity decreased from healthy to mid-atretic oocytes in both MF and SF subpopulations at GV, but in the SF subpopulation at MII, the mitochondrial activity and frequency of oocytes with clustered mitochondria were significantly higher in light-atretic than in healthy oocytes. The light-atretic oocytes also produced more ATP than healthy ones in both SF and MF subpopulations. However, a significantly higher relative abundance of mRNA TFAM was found in SF than MF subpopulations at GV, and this difference remained in mid-atretic oocytes at MII. It can be concluded that meiotic competence and atresia level influence mitochondrial status of immature bovine oocytes. After maturation, healthy oocytes from medium follicles and light-atretic oocytes from small follicles were more developed in terms of mitochondrial status than the other oocytes.

Gene expression differences in oocytes derived from adult and prepubertal Japanese Black cattle during in vitro maturation

The present study was carried out to compare the gene expression profiles in oocytes derived from adult and prepubertal Japanese Black cattle during in vitro maturation (IVM) using microarray gene chips (Bovine genome array containing 24,072 probe sets representing over 23,000 transcripts). Microarray experiments were conducted using total RNA isolated from immature [germinal vesicle (GV)] and in vitro matured [metaphase II, (MII)] oocytes derived from adult and prepubertal animals. A total of 333 (1.4%) and 549 (2.3%) genes were differentially expressed between prepubertal vs adult bovine GV and MII stages oocytes, respectively. Of these, 176 and 312 genes were up-regulated, while 157 and 237 were down-regulated in prepubertal when compared with adult GV and MII oocytes, respectively. It was also observed that 695 (2.9%) and 553 (2.3%) genes were differentially expressed between GV vs MII stage oocytes in the adult and prepubertal groups, respectively. Gene ontological classification of the differentially expressed genes revealed that up-regulated genes in adult oocytes were involved in signal transduction, transcriptional control and transport. Quantitative reverse transcription-PCR validated the expression profile of some selected transcripts and confirmed differences in the expression levels of transcripts between adult vs prepubertal groups in both GV and MII stages oocytes as identified by microarray data analysis. This study indicated for the first time that significant number of genes were differentially expressed (>2-fold, p < 0.01) between oocytes derived from adult and those from prepubertal Japanese Black cattle, and this difference increased during IVM.

Alterations in the transcriptome of porcine oocytes derived from prepubertal and cyclic females is associated with developmental potential

The developmental competence of oocytes is progressively attained as females approach puberty. The poor quality of prepubertally derived oocytes suggests that essential processes during cytoplasmic maturation have not been completed. The objective of this experiment was to identify genes in oocytes that are associated with good (cyclic females) and poor (prepubertal females) developmental competence. Development to the blastocyst stage in vitro was significantly decreased in oocytes derived from prepubertal females compared with cyclic females (5.26 and 12.86%, respectively). Approximately 10% of the oocyte transcriptome was differentially expressed between in vitro-matured oocytes derived from cyclic and prepubertal females (P < 0.05); 58% of differentially expressed genes had increased transcript abundance in oocytes derived from cyclic females. Genes involved in the metabolism and regulation of biological processes had increased transcript abundance in oocytes derived from cyclic females, whereas genes involved in translation were increased in prepubertally derived oocytes. Quantitative PCR confirmed differential expression (P < 0.05) for 6 out of 11 selected genes [DPYD (dihydropyrimidine dehydrogenase), RDH11 (retinol dehydrogenase 11), SFRS4 (serine/arginine-rich splicing factor 4), SFRS7 (serine/arginine-rich splicing factor 7), TL4 (transcribed loci 4), and TOP2B (topoisomerase II β)] that were differentially expressed with greater than a 2-fold change by microarray, although 3 of these genes, DPYD, TL4, and TOP2B, were in opposing directions by the 2 methods. In conclusion, expression of multiple genes involved in metabolism and translation was significantly altered in oocytes from prepubertal females compared with cyclic females, which was associated with reduced in vitro development to the blastocyst stage. These genes may represent important cellular mechanisms that regulate oocyte quality.

Advanced follicle development in xenografted prepubertal ovarian tissue: the common marmoset as a nonhuman primate model for ovarian tissue transplantation

OBJECTIVE

To establish a nonhuman primate model addressing follicular development in cryopreserved prepubertal ovarian tissue after xenografting.

DESIGN

Experimental study.

SETTING

Academic research center.

ANIMAL(S)

Ovarian tissue from female prepubertal common marmoset (Callytrix jacchus jacchus) grafted into immunodeficient nude mice (Crl:NU-FoxnI(nu)).

INTERVENTION(S)

Removal and subsequent cryopreservation of ovarian tissues with dimethyl sulfoxide, followed by grafting to subcutaneous sites of ovariectomized and intact nude mice.

MAIN OUTCOME MEASURE(S)

Histologic evaluation for the mean number of total and morphologically normal follicles in each class.

RESULT(S)

The mean number of unadvanced follicles in frozen-thawed grafted ovarian tissues was reduced compared with pregraft controls, but the prevalence of normal follicular morphology was either slightly increased (primordial follicles) or unchanged (primary follicles). Previous ovariectomy in graft recipients increased total follicle numbers without effect on normal follicular morphology and shifted the ratio of primordial to primary follicles toward an increase in primary follicles, indicating activation of follicular maturation.

CONCLUSION(S)

The marmoset is a suitable primate model for studies on the subsequent use of cryopreserved ovarian tissue, demonstrating graft sustainment and the development of follicles from prepubertal ovarian tissue in immunodeficient hosts up to secondary and preantral stages.

Cryo-survival, fertilization and early embryonic development of vitrified oocytes derived from mice of different reproductive age

PURPOSE

to evaluate the effect of female reproductive age on oocyte cryo-survival, fertilization and the subsequent embryonic development following vitrification using the mouse model in order to address the question of how maternal reproductive age is related to fertility preservation.

METHODS

oocytes were collected from mice of different reproductive age: (1) 8-10 weeks, (2) 16-20 weeks, (3) 32-36 weeks, and (4) 44-48 weeks. Following vitrification and warming, the oocytes in each group were assessed for cryo-survival, fertilization and embryonic development as well as for the quality of blastocysts. Fresh oocytes without undergoing vitrification were used in each age group as controls.

RESULTS

the mean number of oocytes retrieved following superovulation was found to reduce significantly (P < 0.05) in mice from 32-36 weeks of age (18.1 ± 8.5) compared with 8-10 weeks of age (26.8 ± 9.8) and 16-20 weeks of age (23.9 ± 4.2) respectively. The cryo-survival rate of oocytes was reduced significantly (P < 0.05) in mice of 44-48 weeks of age (90.4% ± 7.9) compared with the other 3 groups (98.8% ± 2.1, 98.0% ± 3.3 and 98.5% ± 2.2, respectively). The cleavage rate of vitrified oocytes declined significantly following the increase in maternal age in mice of 32-36 weeks of age (69.7% ± 20.8) forward (63.6% ± 9.2). However, no significant difference in the cleavage rate was found among the control groups of different maternal ages. The rate of embryo development to the blastocyst stage in the vitrified oocytes also significantly declined following the increase in maternal age (71.8% ± 8.8, 66.4% ± 10.7, 64.2% ± 17.4 and 4.1% ± 8.3 respectively). There were no such differences in the rates of embryo development to the blastocyst stage among the control groups following the increase in maternal age (75.9% ± 12.2, 79.5% ± 28.9, 70.2% ± 17.4 and 69.3% ± 19.0 respectively). However, the quality of blastocysts produced from 32-36 weeks and 44-48 weeks of ages was significantly poor in term of total cell numbers and the ratio of inner cell mass(ICM) / trophectoderm (TE) compared to younger age in both vitrified and control groups

CONCLUSIONS

cryo-survival of oocytes following vitrification and warming procedures is associated with female reproductive age. There is a more negative impact on the oocytes following vitrification and warming with the increase of maternal age.

Oocyte secreted factors improve embryo developmental competence of COCs from small follicles in prepubertal goats

Oocytes secrete soluble paracrine factors called Oocyte Secreted Factors (OSFs) which regulate the cumulus cell phenotype. Follicle populations in ovaries from prepubertal females have smaller diameters than their adult counterparts. Oocytes from small follicles are less competent than those from large follicles. The aim of this study was to investigate, in prepubertal goats, the effect of OSFs secreted by denuded oocytes (DOs) from small (<3 mm) or large (>or=3 mm) follicles during IVM on embryo development and the blastocyst quality of cumulus-oocyte complexes (COCs) from small follicles and to determine if GDF9 participates in this process. Treatment groups were: (A) COCs non selected by their follicle size (control group); (B) cumulus oocytes complexes from small follicles (SFCOCs), (C) cumulus oocytes complexes from small follicles co-cultured with denuded oocytes from small follicles (SFCOCs + SFDOs), and (D) cumulus oocytes complexes from small follicles co-cultured with denuded oocytes from large follicles (SFCOCs + LFDOs). The effect of the addition of kinase inhibitor SB-431542, which antagonizes GDF9, was tested in A, C, and D treatment groups. Co-cultured SFCOCs with SFDOs or LFDOs significantly augmented the blastocyst rate in comparison to SFCOCs alone (15.77%, 17.39% vs. 10.31%, respectively). Blastocysts from SFCOCs + LFDOs group showed higher rates of tetraploid nuclei than blastocysts from SFCOCs and the control group (14.43% vs. 5.45% and 5.24%, respectively; P < 0.05). However, we did not observe differences in the hatching rate, mean cell number or embryo cryotolerance (P > 0.05) between the four treatment groups. The addition of SB-431542 during IVM did not have any effect on blastocyst rate (P > 0.05). In conclusion, in prepubertal goats, COCs with a low embryo developmental competence as a consequence of follicle size can be improved by coculturing them with denuded oocytes from both small and large follicles. GDF9 does not seem play a role in this improvement.

Generation of pluripotent stem cells from eggs of aging mice

Oocytes can reprogram genomes to form embryonic stem (ES) cells. Although ES cells largely escape senescence, oocytes themselves do senesce in the ovaries of most mammals. It remains to be determined whether ES cells can be established using eggs from old females, which exhibit reproductive senescence. We attempted to produce pluripotent stem cell lines from artificial activation of eggs (also called pES) from reproductive aged mice, to determine whether maternal aging affects pES cell production and pluripotency. We show that pES cell lines were generated with high efficiency from reproductive aged (old) mice, although parthenogenetic embryos from these mice produced fewer ES clones by initial two passages. Further, pES cell lines generated from old mice showed telomere length, expression of pluripotency molecular markers (Oct4, Nanog, SSEA1), alkaline phosphatase activity, teratoma formation and chimera production similar to young mice. Notably, DNA damage was reduced in pES cells from old mice compared to their progenitor parthenogenetic blastocysts, and did not differ from that of pES cells from young mice. Also, global gene expression differed only minimally between pES cells from young and old mice, in contrast to marked differences in gene expression in eggs from young and old mice. These data demonstrate that eggs from old mice can generate pluripotent stem cells, and suggest that the isolation and in vitro culture of ES cells must select cells with high levels of DNA and telomere integrity, and/or with capacity to repair DNA and telomeres.

Involvement of E-cadherin in early in vitro development of adult and juvenile sheep embryos

The oocyte-to-embryo transition in mammals depends on maternal proteins and transcripts, which accumulate during oocyte differentiation. The aim of the present study was to examine the role of the junctional proteins β-catenin and E-cadherin during preimplantation in vitro embryo development in sheep, comparing the competence of adult and prepubertal oocytes. We analysed the concentration of β-catenin and E-cadherin in immature and in vitro-matured oocytes. There was a significant increase in E-cadherin concentration after 24 h of in vitro maturation and this was lower in prepubertal oocytes than in adult ones. We therefore studied the expression and distribution of E-cadherin during the major transition from maternal to embryonic genome. E-cadherin distribution and localisation in sheep was age- and developmental-stage dependent and was related to developmental kinetics. In fact, in adults, the majority of embryos showed the proper distribution of E-cadherin just beneath the membrane surfaces of all blastomeres and the percentage of embryos with this distribution increased with the increase in cell number during development. On the contrary, and regardless of their developmental stage, the majority of prepubertal embryos showed an uneven distribution of the protein, often associated with the occurrence of cellular fragmentation. In conclusion, our results suggest that E-cadherin plays a pivotal role during preimplantation embryo growth in sheep and may be one of the possible cytoplasmic factors involved in the reduced developmental competence of prepubertal female gametes.

TGF-beta Sma/Mab signaling mutations uncouple reproductive aging from somatic aging

Female reproductive cessation is one of the earliest age-related declines humans experience, occurring in mid-adulthood. Similarly, Caenorhabditis elegans' reproductive span is short relative to its total life span, with reproduction ceasing about a third into its 15–20 day adulthood. All of the known mutations and treatments that extend C. elegans' reproductive period also regulate longevity, suggesting that reproductive span is normally linked to life span. C. elegans has two canonical TGF-ß signaling pathways. We recently found that the TGF-ß Dauer pathway regulates longevity through the Insulin/IGF-1 Signaling (IIS) pathway; here we show that this pathway has a moderate effect on reproductive span. By contrast, TGF-ß Sma/Mab signaling mutants exhibit a substantially extended reproductive period, more than doubling reproductive span in some cases. Sma/Mab mutations extend reproductive span disproportionately to life span and act independently of known regulators of somatic aging, such as Insulin/IGF-1 Signaling and Dietary Restriction. This is the first discovery of a pathway that regulates reproductive span independently of longevity and the first identification of the TGF-ß Sma/Mab pathway as a regulator of reproductive aging. Our results suggest that longevity and reproductive span regulation can be uncoupled, although they appear to normally be linked through regulatory pathways.

Female reproductive cessation is the earliest aging phenotype humans experience, and its importance as a clinical issue is growing as more women opt to have children later in life. While much work has been done to understand the general aging process, little is currently known about the regulation of reproductive aging. Like longevity, the ability to produce progeny with advanced age is likely to be genetically regulated. Thus, understanding the processes that regulate reproductive aging may allow us to address the problems of maternal age-related infertility and birth defects. C. elegans and humans both have long post-reproductive life spans, leaving open the possibility that their reproductive spans might be extendable. C. elegans has been used previously to discover conserved regulators of aging, and here we use worms to identify a new regulator of reproductive aging, a highly conserved TGF-ß signaling pathway. We find that TGF-ß signaling regulates reproductive aging independently of somatic aging. This is the first identification of a pathway that breaks the coupling that normally links the two processes. Our work will provide new insights into the improvement of human fertility and prevention of age-related birth defects, and it has implications for the evolutionary relationship between reproduction and longevity regulation.

Effect of follicle size and dibutyryl cAMP on the cAMP content and gap junctional communication of porcine prepubertal cumulus-oocyte complexes during IVM

The lower ability of oocytes from prepubertal pigs to yield viable embryos than those from adult pigs appears, in part, a consequence of their reduced ability to accumulate cAMP during IVM. The present study examined the cAMP content of oocytes and cumulus-oocyte complexes (COCs), cumulus expansion and gap junctional communication (GJC) in COCs from 3- and 5-8-mm follicles during IVM. The effect of 1 mm dibutyryl cAMP (db-cAMP) treatment for the first 22 h of IVM was also examined for both follicle size classes. The cAMP concentration of oocytes from 5-8-mm follicles was threefold greater than that in oocytes from 3-mm follicles following 11 h of IVM (11.9 +/- 5.9 v. 3.6 +/- 1.8 fmol, respectively; P < 0.05). In the presence of db-cAMP, the cAMP content of oocytes from 3- and 5-8-mm follicles was no longer significantly different at 11 h IVM. The cAMP concentration of intact COCs from 5-8-mm follicles was significantly higher than that in COCs from 3-mm follicles at 11 h (1110.6 +/- 318.0 v. 116.9 +/- 55.7 fmol, respectively; P < 0.05). Despite maturation with db-cAMP, the cAMP content in COCs from 3- and 5-8-mm follicles at 11 h of IVM remained significantly different (15.1 +/- 4.9 v. 196.2 +/- 33.3 fmol, respectively; P < 0.05). The COCs from 3-mm follicles displayed lower cumulus expansion than did COCs from 5-8-mm follicles at both 11 h (cumulus expansion index (CEI) 1.0 +/- 0.1 v. 1.8 +/- 0.1, respectively; P < 0.01) and 22 h (CEI 1.9 +/- 0.3 v. 2.9 +/- 0.2, respectively; P < 0.05) of IVM. The level of cumulus cell-oocyte GJC decreased during IVM, with the number of GJC significantly greater in COCs from 3-mm compared with 5-8-mm follicles at both 6 h (613 +/- 55 v. 304 +/- 44 fluorescence intensity (FI), respectively; P < 0.05) and 11 h (644 +/- 99 v. 337 +/- 38 FI, respectively; P < 0.05) of IVM. By 22 h of IVM, the GJC of COCs from 3-mm follicles had decreased (227 +/- 18 FI) and was no longer significantly different to that of COCs from 5-8-mm follicles (139 +/- 15 FI; P > 0.05). Dibutyryl cAMP had no effect on the cAMP content, cumulus expansion or GJC of the whole COC. In conclusion, the results of the present study demonstrate that COCs from 3-mm follicles accumulate less intraoocyte and inter-COC cAMP, display lower cumulus expansion and maintain their cumulus cell-oocyte GJC for longer during IVM than do COCs from 5-8-mm follicles.

Induction of lamb follicular development and embryo production in vitro

Effect of lamb age, transport stimulation and repeated hormone superovulation on the number of collected oocytes were determined. Effect of the culture medium containing ethylenediaminetetraacetic acid (EDTA) on the development of embryos produced in vitro from lamb oocytes was also investigated. Results indicated that the mean numbers of collected and available oocytes (oocytes with compacted cumulus cells, evenly granulated ooplasm and morphologically normal) from 6- to 8-week-old lambs were 60.8±13.9 and 58.2±12.3, respectively. These figures were higher than those obtained from 12- to 14-week-old lambs (27.3±5.1 and 26.0±4.9) (P<0.05). Stimulation by transportation didn't decrease the number of collected oocytes from the superovulated lambs (P>0.05). However, the number of collected oocytes in the repeated superovulation group was significantly reduced, compared with the control group (P<0.05). The embryonic culture medium supplemented with 10 μmol/l EDTA highly improved the development capability of the embryos from lamb oocytes (P<0.05). Healthy lambs were born following embryo transfer.

Effects of age and equine follicle-stimulating hormone (eFSH) on collection and viability of equine oocytes assessed by morphology and developmental competency after intracytoplasmic sperm injection (ICSI)

Young (4 to 9 yr) and old (≥20 yr) mares were treated with equine follicle-stimulating hormone (eFSH), and oocytes were collected for intracytoplasmic sperm injections (ICSI). Objectives were to compare: (1) number, morphology and developmental potential of oocytes collected from young v. old mares from cycles with or without exogenous eFSH and (2) oocyte morphology parameters with developmental competence. Oocytes were collected from preovulatory follicles 20 to 24 h after administration of recombinant equine LH and imaged before ICSI for morphological measurements. After ICSI, embryo development was assessed, and late morulae or blastocysts were transferred into recipients’ uteri. Cycles with eFSH treatment resulted in more follicles (1.8 v. 1.2) and more recovered oocytes (1.1 v. 0.8) than those without eFSH. Age and eFSH treatment did not effect cleavage, blastocyst and pregnancy rates. Treatment with eFSH had no effect on oocyte morphology, but age-associated changes were observed. In old mares, zona pellucidae (ZP) were thinner than in young mares, and perivitelline space and inner ZP volume (central cavity within the ZP) were larger and associated with oocytes that failed to develop. These results suggest that administration of eFSH can increase the number of oocytes collected per cycle. Oocyte morphology differed with age and was associated with developmental competence.

Developmental capabilities of embryos produced in vitro from prepubertal lamb oocytes

Breeding from prepubertal females, known as juvenile in vitro embryo transfer (JIVET), reduces the generation interval and increases the rate of genetic gain in animal breeding programs. While the birth of the first lambs from prepubertal ewes occurred nearly 30 years ago; and there is considerable interest in the commercialization of this technology, its efficiency remains too low. The advent of in vitro production (IVP) of embryo resulted in the more widespread use of JIVET. Morphologic and metabolic differences coupled with reduced in vitro and in vivo development of oocytes derived from prepubertal animals have been reported. Research has been undertaken to optimize donor selection and hormone stimulation methods in an attempt to reduce the variability and increase the proportion of donors responding to hormone stimulation and increase oocyte developmental competence. Yet, this variation persists and the development of oocytes and embryos from prepubertal animals remains reduced when compared with adults. Recent improvements to JIVET, resulting from a modified hormone stimulation regime, have eliminated the failure of donors to respond to hormone stimulation, and increased both the number and developmental competence of oocytes harvested from very young prepubertal lambs. This increased efficiency has facilitated the incorporation of other reproductive technologies such as sperm sexing with JIVET, resulting in the birth of lambs of a pre-determined sex from prepubertal lambs. Increased rates of genetic gain in sheep breeding programs can be achieved by combining sexed sperm with oocytes obtained from lambs as young as 3-4 weeks of age. Continued increases in the efficiency of JIVET resulting from further improvements to hormone stimulation regimes and an increased understanding of the differences between oocytes from adult and prepubertal animals will result in the commercialization of this technology.

Ovarian follicular dynamics: a review with emphasis on the bovine species. Part I: Folliculogenesis and pre-antral follicle development

Recent scientific research into pre-antral follicular dynamics has resulted in the discovery of a wide range of hormones and local factors that influence primordial follicle activation and contribute to follicular development. The putative role of several of these mediators in the follicle growth process has been elucidated by genetic and molecular investigations. Crucial questions, such as the mechanism for primordial follicle initiation and the interplay between oocyte and granulosa cells in this process, remain however unresolved. This review article commences with a description of the embryogenesis of the ovary and follicles. Next, the different stages in the development from primordial to pre-antral follicle are discussed. Thereafter, a short overview of the various in vitro models for the study of follicular dynamics is presented. Finally, an in-depth discussion of pre-antral follicle development engages in the current hypotheses regarding primordial follicle activation, and the role of gonadotrophins and angiogenesis.

Juvenile and adult immature and in vitro matured ovine oocytes evaluated in relation to membrane electrical properties, calcium stores, IP3 sensitivity and apoptosis occurrence in cumulus cells

The analysis of differences between juvenile and adult oocytes may provide useful information on the acquisition of meiotic and developmental competence of the female gamete. In oocytes collected from either ewes or 40-day-old lambs, we evaluated membrane electrical properties, such as resting potential, conductance, activation ion currents, L-type Ca(2+) currents as well as calcium stores and IP3 sensitivity; in addition, the incidence of apoptosis in cumulus cells in these two age categories was compared. The analysis was carried out in oocytes both prior to and after in vitro maturation. Significant differences were found in all the examined parameters in relation to maturational stages whereas minor differences were recorded in relation to age of the donor. IP3 sensitivity strongly increased after in vitro maturation following a dose-dependent pattern from 1 to 500 micromol/L with a significant interaction (P < 0.01) between dose and maturational stage. The incidence of apoptosis in cumulus cells strongly increased after in vitro maturation and was greater in adult than in juvenile cumulus cells (39.2 +/- 5.8% vs. 21.9 +/- 3.5%; P < 0.01). In conclusion, all the examined parameters were greatly affected by the maturational stage, whereas minor differences were due to age-related oocyte quality, that is, at plasma membrane levels to conductance, activation current peaks and calcium currents, at cytosol level to calcium stores and IP3 sensitivity, and to incidence of apoptosis in cumulus cells. These parameters were compared with previous data in bovine to analyze oocyte quality in juvenile and adult individuals or between species.

Apoptosis maintains oocyte quality in aging Caenorhabditis elegans females

In women, oocytes arrest development at the end of prophase of meiosis I and remain quiescent for years. Over time, the quality and quantity of these oocytes decreases, resulting in fewer pregnancies and an increased occurrence of birth defects. We used the nematode Caenorhabditis elegans to study how oocyte quality is regulated during aging. To assay quality, we determine the fraction of oocytes that produce viable eggs after fertilization. Our results show that oocyte quality declines in aging nematodes, as in humans. This decline affects oocytes arrested in late prophase, waiting for a signal to mature, and also oocytes that develop later in life. Furthermore, mutations that block all cell deaths result in a severe, early decline in oocyte quality, and this effect increases with age. However, mutations that block only somatic cell deaths or DNA-damage-induced deaths do not lower oocyte quality. Two lines of evidence imply that most developmentally programmed germ cell deaths promote the proper allocation of resources among oocytes, rather than eliminate oocytes with damaged chromosomes. First, oocyte quality is lowered by mutations that do not prevent germ cell deaths but do block the engulfment and recycling of cell corpses. Second, the decrease in quality caused by apoptosis mutants is mirrored by a decrease in the size of many mature oocytes. We conclude that competition for resources is a serious problem in aging germ lines, and that apoptosis helps alleviate this problem.

Effects of insulin-like growth factor-I, epidermal growth factor and cysteamine on the in vitro maturation and development of oocytes collected from 6- to 8-week-old Merino lambs

To improve the viability of embryos produced in vitro from lamb oocytes, maturation medium was supplemented with insulin-like growth factor-I (IGF-I), epidermal growth factor (EGF), cysteamine, and combinations thereof. Experiment 1 examined the effects of IGF-I supplementation and duration of oocyte maturation on nuclear maturation and embryo development while Experiments 2 and 3 examined the effects of cysteamine and EGF supplementation respectively on embryo development. In Experiment 4, embryo development was examined after maturation with various combinations of supplements. IGF-I supplementation increased cleavage rate (P < 0.05) but its effect on the rate of blastocyst production from original oocytes was variable. Supplementation with IGF-I increased (P < 0.01) the proportion of oocytes at Metaphase II (MII) after 18 h of maturation but not at later times. EGF either alone or combined with IGF-I significantly (P < 0.05) increased cleavage rates compared with other treatment groups but EGF consistently failed to improve blastocyst production rates. Cysteamine improved hatching rates but only when supplemented alone. Maturation of lamb oocytes for 22 h in medium supplemented with 100 ng mL(-1) IGF-I and 100 microm cysteamine resulted in the production of 16.0 lambs per donor lamb after embryos were transferred to recipient ewes. It is concluded that EGF and, to a lesser extent, IGF-I, whilst beneficial to initial cleavage, can adversely influence subsequent embryo development. Improvements in embryo viability may more likely be obtained by addressing issues that influence fetal oocyte quality than by modifying in vitro methodology.

Relationship between follicle size and oocyte developmental competence in prepubertal and adult pigs

The present study compared the distribution and steroid composition of 3-, 4- and 5-8-mm follicles on the surface of prepubertal and adult ovaries, and determined the relationship between follicle size and developmental competence of oocytes following parthenogenetic activation. The effect of 1 mm dibutyryl cAMP (dbcAMP) for the first 22 h of in vitro maturation (IVM) on the embryo development of prepubertal oocytes from the three follicle size cohorts was also determined. Compared with adult, prepubertal ovaries contained a higher proportion of 3-mm follicles (46 v. 72%, respectively), but a lower proportion of 4-mm (33 v. 22%, respectively) and 5-8-mm follicles (21 v. 6%, respectively). Adult follicular fluid (FF) contained 11-fold higher levels of progesterone (P4) than prepubertal FF, with similar levels observed between all adult follicle sizes. In prepubertal FF, the P4 concentration increased with follicle size from 3 to 4 to 5-8 mm. Rates of blastocyst development following parthenogenetic activation of adult oocytes from all three follicles sizes were similar (approximately 55%), whereas rates from prepubertal oocytes increased with increasing follicle size from 3 (17%) to 4 (36%) to 5-8 mm (55%). Treatment with dbcAMP for the first 22 h of IVM led to a 1.5-fold increase in the rate of blastocyst development for prepubertal oocytes from 3-mm follicles, but had no effect on prepubertal oocytes from the 4 and 5-8 mm classes. Mean blastocyst cell number increased with follicle size in prepubertal ovaries and was similar for all follicle sizes in adult ovaries. The present study demonstrates that the low efficiency of in vitro embryo production observed using prepubertal compared with adult pig oocytes is due to a greater proportion of 3-mm follicles on prepubertal ovaries, which contain oocytes of inferior developmental competence.

Total RNA and protein content, Cyclin B1 expression and developmental competence of prepubertal goat oocytes

The aim of this study was to examine the relationship between the developmental competence of oocytes and their total RNA and protein contents, and the level of Cyclin B1 transcription. Ovaries from prepubertal goats were collected from a slaughterhouse. Oocytes were recovered by slicing and those with two or more layers of cumulus cells and homogenous cytoplasm were matured in vitro (20-25 oocytes per drop) for 27 h. Both before and after IVM, samples of oocytes were denuded and categorised into four group treatments by diameter (<110 microm, 110-125 microm, 125-135 microm; >135 microm), separated into sub-groups of 10 oocytes per treatment-replicate and stored in liquid nitrogen until total RNA content analysis by spectophotometry, total protein content analysis by a colorimetric assay and Cyclin B1 transcription analysis by RT-PCR. For the study of developmental competence, the rest of the matured oocytes were fertilised in vitro in groups of 20-25 for 24 h. Presumptive zygotes were denuded, sorted into the four categories of diameter noted above, and placed into culture drops in groups of 18-25 for in vitro culture. Cleavage rate was evaluated at 48 hpi and embryo development at 8 d post-insemination. There were four replicates of each treatment for each assay or evaluation point of the experiment. There were no significant differences between the size categories of oocytes at collection in total RNA content, total protein content and Cyclin B1 mRNA. There were significant differences (P<0.05) in the expression of Cyclin B1 before IVM with oocytes in the >135 mm diameter category having the highest value for this variant. There were no significant differences in these characteristics between the categories of oocyte diameter after IVM except in respect of total RNA content, which was lower for the largest size of oocytes (>135 microm; mean+/-S.D.=12.3+/-1.84 ng/oocyte) than the other three size groups (19.2+/-1.38-22.1+/-4.44 ng/oocyte; P<0.05). Significant differences (P<0.05) in cleavage rate were observed between the different oocyte size categories (<110 microm, 3.0%; 110-125 microm, 32%; 125-135 microm, 50%; >135 microm, 73%). Only oocytes >125 microm diameter developed to the blastocyst stage (125-135 microm, 7%; >135 microm, 10%). This study showed that the RNA content and the Cyclin B1 RNA expression of prepubertal goat oocytes, and their development to embryos varied between the different size categories of the oocytes.

Gilts and sows produce similar rate of diploid oocytes in vitro whereas the incidence of aneuploidy differs significantly

Oocytes derived from prepubertal gilts show reduced developmental competence when compared to oocytes collected from adult sows. Therefore, the aim of the study was to investigate whether gilts (4-5 months old) and adult sows (average age 3.5 years) of the same breed (Polish Landrace x Polish Large White crossbred) differ with regard to the rate of chromosomally unbalanced oocytes after IVM. COCs derived from individual pairs of slaughterhouse ovaries were matured in vitro and analyzed cytogenetically by conventional staining (Giemsa) and FISH methods (probes corresponding to centromeric regions of pig chromosomes 1 and 10). Altogether, 72 females (31 sows, 41 gilts) and 430 secondary oocytes (194 and 236 oocytes of sows and gilts, respectively) were investigated. Cytogenetic analysis revealed diploid (Giemsa, FISH) and aneuploid (FISH) spreads. The incidence of diploid oocytes was similar for sows (26.0%) and gilts (24.5%) whereas the rate of aneuploid oocytes (nullisomic/disomic) was eight times higher in gilts (10.8%) than in sows (1.3%). Diploid and aneuploid oocytes were observed in 64% of investigated females. Pig chromosome 10 was more frequently disomic/nullisomic compared to chromosome 1 suggesting, that like in human, small porcine chromosomes are often involved in the nondisjunction process. In conclusion, chromosomal imbalance significantly contributes to in vitro embryo production in the pig, since over 60% of females produced diploid or aneuploid gametes. The significantly higher rate of aneuploidy among oocytes derived from gilt ovaries may contribute to the reduced developmental competence of gametes collected from nonmature female pigs.

Retrospective analysis of 1217 IVF cycles in women aged 40 years and older

Older women comprise an increasing portion of patients entering assisted reproduction programmes. This study is a retrospective summary of the files of all patients aged 40 years and older at advent of IVF, between 1995 and 2004, in the authors' centre. In all, 381 women underwent 1217 initiated treatment cycles. Embryo transfer was performed in 62.6% of initiated cycles. Success rates declined with each year after age 40; pregnancy and delivery rates were 13.9 and 9.1% at age 40 and 2.8 and 0.7% at age 45. There were no deliveries at an older age. Logistic regression analysis showed the following factors were independently and significantly related to higher pregnancy rates: younger age, lower dose of gonadotrophins, greater number of mature follicles, endometrial thickness, and number of embryos transferred; prior pregnancy did not influence success. Retrieving more than four oocytes increased pregnancy rates in all women over 40. Transferring 3 embryos or more increased pregnancy rates in all ages, but reached statistical significance only in women aged 40-41 (P < 0.000). It is concluded that in women between 40 and 41 years of age, ovarian response is a major determinant of success, but not in women older than that. Unrealistic expectations may be avoided if accurate data are provided regarding delivery rates per year after age 40.

Prise en charge en Assistance médicale à la procréation des femmes de 38 ans et plus: résultats d'une enquête à propos de 84 couples

OBJECTIVE

More and more young women are delaying childbearing until the fourth decade of life: thus, Assisted Reproductive Techniques centres receive more and more requests from ageing women. The aim of the study is to analyse the purpose of these requests, the biological and clinical features of these patients and the results in our infertility centre.

PATIENTS AND METHODS

A retrospective study was carried out at the CHU of Saint-Etienne from 01.01.01 to 31.12.04. We analysed the social, clinical and biological features of 84 couples when the woman's age was equal or superior to 38 years, representing 218 cycles. A questionnaire was used to collect social data.

RESULTS

Several factors can explain the increasing number of ageing women consulting for infertility: extend university time and professional career, professional stability, contraception and late meeting of the partner, false reassuring information concerning progress in ART, second child desire after a late first pregnancy, but also second marital unions and child desire in the redefined couple. In our study, above 40 years old, the pregnancy (19.4 versus 10.5%) and delivery rates (16.7 versus 5.8%) clearly decreased in IUI. Thus, most of the clinicians propose, in first choice, an IVF cycle to a 40 year-old woman. The ultrasound measurement of antral follicle count can accurately evaluate the prognosis in terms of pregnancy (P<0.01) and delivery rate (P=0.03). For patients with unfavourable prognosis, oocyte donation, embryo donation, or adoption can be considered.

DISCUSSION AND CONCLUSION

ART cannot compensate for the natural decrease in pregnancy rates and the increase in early miscarriages in ageing women. Therefore, it is essential to inform young women of the negative effects of age on their potential fertility.

Effect of oocyte diameter on meiotic competence, embryo development, p34 (cdc2) expression and MPF activity in prepubertal goat oocytes

The aim of this study was to analyze the relationship between oocyte diameter, meiotic and embryo developmental competence and the expression of the catalytic subunit of MPF, the p34(cdc2), at mRNA, RNA and protein level, as well as its kinase activity, in prepubertal (1-2 months old) goat oocytes. MPF is the main meiotic regulator and a possible regulator of cytoplasmic maturation; therefore, it could be a key factor in understanding the differences between competent and incompetent oocytes. Oocytes were classified according to oocyte diameter in four categories: <110, 110-125, 125-135 and >135 microm and matured, fertilized and cultured in vitro. The p34(cdc2) was analyzed in oocytes at the time of collection (0 h) and after 27 h of IVM (27 h) in each of the oocyte diameter categories. The oocyte diameter was positively related to the percentage of oocytes at MII after IVM (0, 20.7, 58 and 78%, respectively) and the percentage of blastocysts obtained at 8 days postinsemination (0, 0, 1.95 and 12.5%, respectively). The expression of RNA and mRNA p34(cdc2) did not vary between oocyte diameters at 0 and 27h. Protein expression of p34(cdc2) increased in each oocyte category after 27 h of maturation. MPF activity among diameter groups did not vary at 0h but after IVM there was a clear and statistically significant increase of MPF activity in the biggest oocytes.

Effect of GnRH treatment on the maturation and in vitro development of oocytes collected from 4- to 6-week-old Merino lambs

Two experiments were conducted in Merino lambs to examine the effects of gonadotrophin-releasing hormone (GnRH) treatment on the developmental competence of oocytes collected after pretreatment with follicle stimulating hormone (FSH). The first experiment examined the effects of six GnRH treatment times (control and GnRH administered 2, 4, 6, 8 and 10 h before oocyte collection) and four in vitro maturation (IVM) periods (18, 20, 22, 24 h) on the rate of oocyte nuclear maturation. The second experiment examined the effect of five GnRH treatment times (control and GnRH administered 2, 4, 6 and 8 h before oocyte collection) and three IVM periods (20, 22, 24 h) on the development of oocytes and embryos after in vitro maturation, fertilisation and culture. In Experiment 1, GnRH treatment did not influence the mean number of cumulus-oocyte-complexes (COCs) collected or COC morphology at the time of collection. However, treatment changed (P < 0.01) the distribution of follicle size and this was primarily due to a marked reduction in the number of follicles with diameters <2 mm. In addition, GnRH treatment at 6 and 8 h increased (P < 0.01) the proportion of oocytes that developed to Metaphase II (MII) (63.2 and 72.6%, respectively) compared with other treatment times (range 52.9–59.9%). Nuclear maturation was influenced by a significant (P < 0.05) interaction between GnRH treatment and IVM period due to a disproportionately greater number of oocytes at the germinal vesicle breakdown (GVBD) stage for the 2 and 4 h GnRH treatments compared with other treatments. In Experiment 2, cleavage rate (range 63.5–85.9%) was highest when GnRH was administered 8 h before collection but the percentage of cleaved oocytes that developed into blastocysts (range 10.0–35.0%) was significantly (P < 0.05) lower for the 6 and 8 h GnRH treatments compared with the control and the 2 h GnRH treatment. These results demonstrate that GnRH treatment before oocyte collection can improve nuclear maturation and cleavage rates in lamb oocytes but that these improvements are not reflected in improved rates of blastocyst development. It is speculated that this discrepancy may result from GnRH treatment either adversely affecting cytoplasmic maturation or inducing asynchrony between the maturation of the nuclear and cytoplasmic components of the oocyte.

Effects of pre-treating in vitro-matured bovine oocytes with the cytoskeleton stabilizing agent taxol prior to vitrification

The purpose of this study was to determine the efficacy of pre-treating mature bovine oocytes with Taxol before vitrification by the open pulled Straw method (OPS). We evaluated the effects of pre-treating the oocytes with 1 microM Taxol on chromosome organization, spindle morphology, cortical granule distribution and the ability of fertilized oocytes to develop to the blastocyst stage. After calf or cow oocyte vitrification without Taxol, significantly higher proportions of spindle abnormalities in the form of abnormal spindle structures or dispersed or decondensed chromosomes were observed compared to fresh control oocytes. In contrast, when we compared calf oocytes pre-treated with Taxol before vitrification with control calf oocytes, similar percentages of oocytes showing a normal spindle morphology were observed. The percentages of oocytes with a peripheral cortical granule (CG) distribution increased when the oocytes were pretreated with Taxol and vitrified, while oocytes vitrified without Taxol pre-treatment gave rise to higher cortical distribution percentages. Cleavage and blastocyst rates were significantly lower for vitrified versus untreated oocytes, both in cow and calf oocytes. Significantly higher cleavage rates were obtained when calf and cow oocytes were vitrified with Taxol. Pre-treatment with Taxol before cow oocyte vitrification yielded significantly higher blastocyst rates. Calf oocytes, however, were unable to develop to the blastocyst stage, irrespective of previous Taxol treatment. These results indicate that the pre-treatment of oocytes with Taxol before vitrification helps to reduce the damage induced by the cryopreservation process, and potentially improves the subsequent development of vitrified bovine oocytes. Summary sentence: Pre-treatment of oocytes with Taxol before vitrification helps to reduce the damage induced by vitrification and potentially improves the development of vitrified bovine oocytes.