The protocol followed results in high rates of survival and potential for in-vitro maturation, but has a deleterious effect on the organization of the meiotic spindle of human oocytes cryopreserved at both the GV and MII stages.

A multicentric study was carried out to analyse in a large series: (i) the chromosomal status of unfertilized oocytes, (ii) errors at fertilization and (iii) the chromosomal complement of cleaved embryos. Parameters such as type of sterility, maternal age, stimulation treatment, doses of gonadotrophins administered and oocyte preincubation time before insemination were studied in relation to the incidence of chromosome abnormalities. Twenty-six per cent of the unfertilized oocytes and 29.2% of the embryos had chromosome anomalies. Maternal age significantly increased the rate of aneuploidy in oocytes: 38% in patients over 35 years (versus 24% in younger patients). Fertilization-related abnormalities were significant, i.e. 1.6% parthenogenesis and 6.4% polyploidy. Unexplained infertility was correlated with an increase in the rate of parthenogenesis (4.2%) when compared with tubal infertility (1.2%). Triploidy was found to be correlated with three parameters. A lower rate of triploidy was observed in the group of couples referred because of male sterility (1.9% versus 6.3% for tubal sterility), in HMG-treated patients (2.4% versus 7% with analogues of LHRH/HMG) and with a short 2-h preincubation time before insemination (3% versus 7.2% for greater than 2 h). A general model for natural selection against embryos carrying a chromosome imbalance was proposed.

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Reprogramming of differentiated nuclei into a totipotent embryonic state following somatic cell nuclear transfer (SCNT) is not efficient. Previous studies in the hybrid B6D2F1 mouse strain revealed that a transient treatment of the SCNT embryos with the histone deacetylase inhibitor (HDACi) trichostatin A (TSA) significantly enhance the potential of the cloned embryos to develop in vitro and to term. Here, we compare two different SCNT protocols with TSA and explore, for the first time, the effect of another HDACi, valproic acid (VPA), on the in vitro development, blastocyst quality, and full-term development of mouse B6CBAF1 cloned embryos. Rates of blastocyst development in SCNT embryos treated with either 5 nM TSA during and after activation (31.8%) or with 100 nM TSA or 2 mM VPA before and during activation (34.5 and 38.3%, respectively) were clearly superior to those of nontreated SCNT embryos (22.9-25.1%). These increased in vitro development rates of the HDACi-treated embryos were correlated with an increased level of histone H3 lysine 14 acetylation and an improved blastocyst quality, as judged by the increased number of total and ICM cells in comparison to the nontreated embryos (30-35% increase). Treatment of SCNT embryos with TSA or VPA also allowed the obtention of viable cloned mice, whereas none could be produced from untreated SCNT embryos. In conclusion, we have demonstrated for the first time that VPA can improve the in vitro and full-term development of B6CBAF1 SCNT embryos, at a similar level as TSA. Our findings may open new opportunities to improve cloning efficiencies in other mouse strains or species.

SummaryA new methodology for blastocyst biopsy that uses a 1.48μm in diode laser is described. Trophectoderm cells are biopsied after laster zona drilling and culture, fixed and processed for fluorescent in situ hybridisation (FISH) analysis. Preliminary results on the efficiency of the procedure and blastocyst recovery rate are promising. Blastocyst laser biopsy is a useful tool in preimplantation genetic diagnosis (PGD) as it allows a more reliable diagnosis and widens the diagnostic possibilities on account of the higher number of cells obtained in the biopsy.