The chromosome pattern of embryos derived from tripronuclear zygotes studied by cytogenetic analysis and fluorescence in situ hybridization**Presented at the Conjoint Meeting of The American Fertility Society and the Canadian Fertility and Andrology Society, Montreal, Quebec, Canada, October 11 to 14, 1993.††Supported by grant 83–1069 from the British Columbia Health Care Research Foundation, Vancouver, British Columbia, Canada

Analysis of the first mitotic spindles in human in vitro fertilized tripronuclear zygotes after pronuclear removal

Tripronuclear zygotes (3PN) occur in about 5% of cases in human IVF programmes. Human 3PN zygotes derived from a conventional IVF programme may contain not only the extra male pronucleus but also a supplementary centriole. Researchers have tried to restore diploidy by removing the extra male pronucleus of the tripronuclear zygote. However, it is still unknown whether the procedure can remove the supernumerary centriole. The objective of this study was to evaluate the safety of this manipulation by analysing the first mitotic spindles of 3PN zygotes that have undergone extra pronuclear removal. A controlled trial was conducted using human 3PN zygotes from conventional IVF treatment. In the experimental group, the assumed extra male pronuclei in the 3PN zygotes were removed. The first cleavage patterns and in vitro development were observed in both groups; polarized light microscopy and immunocytochemistry were used to analyse the first mitotic spindles. The blastocyst formation rate was significantly higher (P = 0.007) in the pronuclear-removed group (16.0%) than in the control group (4.5%). No significant differences were found between the groups in the first cleavage patterns and the distributions of the first mitotic spindle structure. This study suggests that, after extra pronuclei are removed, the developmental potential of human 3PN zygotes is improved. However, the abnormal patterns in the first mitosis are not corrected by this removal.

Origin and outcome of pregnancies affected by androgenetic/biparental chimerism

BACKGROUND

Androgenetic diploid cells confined to the placenta have recently been reported in several cases of normally developed fetuses in association with placental mesenchymal dysplasia (PMD).

METHODS AND RESULTS

We investigated two singleton, mildly growth-restricted, female pregnancies ascertained on the basis of PMD. One case had liver hemangiomas and both infants had multiple skin hemangiomas. Post-natal development was normal. Molecular marker analysis confirmed the diagnosis of androgenetic and normal mixed cell populations in the placenta. Both cases derived from a single maternal genome (M1) and two distinct paternal genomes (P1 and P2). In one case, the androgenetic cell population contained both paternal genomes (P1P2), with one shared in common with the biparental (M1P1) population. In the second case, the androgenetic lineage showed complete homozygosity (P2P2) for a paternal genome not common to the biparental cell population.

CONCLUSION

These new PMD cases help to define the range of possible clinical presentations of androgenetic/biparental mosaicism or chimerism. Placentas with androgenetic/biparental chimeric cell populations may derive from a single tri-pronuclear (3PN) zygote in which one or more parental genomes are not equally apportioned to the daughter cells in the first cell division.

Aneuploid analysis of tripronuclear zygotes derived from in vitro fertilization and intracytoplasmic sperm injection in humans

This study demonstrates that the diploid ratio of tripronuclear zygotes after intracytoplasmic sperm injection (ICSI) is significantly higher as compared with that after conventional IVF; the extra pronucleus of tripronuclear zygotes after ICSI are mostly from the second polar body, not from sperm.

Fertilization abnormalities following human in vitro fertilization and intracytoplasmic sperm injection

Fertilization abnormalities are commonly encountered following in vitro fertilization. The widespread introduction of assisted fertilization methods has rapidly led to a changes in both the incidence and types of these aberrations. Such abnormalities can be identified by careful morphological evaluation at the early zygote stage, of pronuclei as well as of polar body formation, and may be confirmed by cytogenetic assessment. The recognition and understanding of fertilization abnormalities have led to the development of novel techniques aimed at preventing them, as well as recent bold attempts at correction. Removal of one pronucleus may allow some triploid embryos to revert to a normal diploid stage. These new developments should provide insight into the understanding of parthenogenesis, androgenesis, and gynogenesis in the human. Microsc. Res. Tech. 61:358-361, 2003.

Bovine embryos contain a higher proportion of polyploid cells in the trophectoderm than in the embryonic disc

The frequency of polyploid cells in the embryonic disc (ED) and in the trophectoderm (TE) was assessed in 50 in vitro produced bovine embryos fixed at days 7-8 post insemination (pi) and in 20 in vitro produced embryos that were transferred to uteri of recipients at day 7 and then recovered and fixed at day 12 pi. Separation of TE and ED cells was obtained by microdissection and the frequency of polyploid cells was determined by interphase cytogenetic analysis using fluorescence in situ hybridization (FISH) with chromosome 6- and chromosome 7-specific probes. The results show that 96% of day 7 embryos contain polyploid cells in the TE, whereas only 58% contain polyploid cells in the ED. In day 12 embryos 85% of TE and 40% of ED preparations contain polyploid cells. Statistical analysis revealed that the frequency of polyploid cells was significantly higher in the TE than in the ED in embryos containing less than 25% polyploid cells (n = 65). The few embryos (n = 5), which contained more than 25% polyploid cells, did not show this difference. Further, it was revealed that the level of polyploidy on day 7-8 was significantly higher than on day 12, both in the TE (two-fold) and in the ED (seven-fold).

Investigation of effects of pregnant mare serum gonadotropin (PMSG) on the chromosomal complement of CD-1 mouse embryos

PURPOSE

The objective of this study was to examine the effect of superovulatory doses of gonadotropins on the frequency of chromosomal abnormalities of mouse embryos.

METHODS

Chromosome analysis of 8- to 16-cell stage mouse embryos and zygotes was performed by a cytogenetic method.

RESULTS

There was no significant effect of the pregnant mare serum gonadotropin (PMSG) dose on the level of aneuploidy and structural abnormalities from 8- to 16-cell-stage embryos among superovulated groups. However, a simple dose-response relationship between the PMSG dose and the incidence of polyploidy was observed, with the level of polyploidy rising from 2.9% with 10 i.u. PMSG to 10.5% with 15 i.u. PMSG. In zygote stage, the proportion of polyploid embryos also increased as the dose increased, from 1.9% in 5 i.u. to 6.7% in 15 i.u. PMSG. It was observed that the extra chromosomal set in polyploidy embryos originated by both fertilization of a diploid oocyte and dispermy.

CONCLUSIONS

These results indicate a dose-response relationship between the PMSG dose and the incidence of polyploidy in the CD-1 mouse. Both a disturbance at maturation division and an error at fertilization were the cause of polyploidy.