The cleavage rate of digynic triploid mouse embryos during the preimplantation period

Unravelling the mystery of female meiotic drive: where we are

Female meiotic drive is the phenomenon where a selfish genetic element alters chromosome segregation during female meiosis to segregate to the egg and transmit to the next generation more frequently than Mendelian expectation. While several examples of female meiotic drive have been known for many decades, a molecular understanding of the underlying mechanisms has been elusive. Recent advances in this area in several model species prompts a comparative re-examination of these drive systems. In this review, we compare female meiotic drive of several animal and plant species, highlighting pertinent similarities.

Spindle assembly checkpoint-related failure perturbs early embryonic divisions and reduces reproductive performance of LT/Sv mice

The phenotype of the LT/Sv strain of mice is manifested by abnormalities in oocyte meiotic cell-cycle, spontaneous parthenogenetic activation, teratomas formation, and frequent occurrence of embryonic triploidy. These abnormalities lead to the low rate of reproductive success. Recently, metaphase I arrest of LT/Sv oocytes has been attributed to the inability to timely inactivate the spindle assembly checkpoint (SAC). As differences in meiotic and mitotic SAC functioning were described, it remains obscure whether this abnormality is limited to the meiosis or also impinges on the mitotic divisions of LT/Sv embryos. Here, we show that a failure to inactivate SAC affects mitoses during preimplantation development of LT/Sv embryos. This is manifested by the prolonged localization of MAD2L1 on kinetochores of mitotic chromosomes and abnormally lengthened early embryonic M-phases. Moreover, LT/Sv embryos exhibit elevated frequency of abnormal chromosome separation during the first mitotic division. These abnormalities participate in severe impairment of preimplantation development and significantly decrease the reproductive success of this strain of mice. Thus, the common meiosis and mitosis SAC-related failure participates in a complex LT/Sv phenotype.

Effect of volume of oocyte cytoplasm on embryo development after parthenogenetic activation, intracytoplasmic sperm injection, or somatic cell nuclear transfer

Animal cloning methods are now well described and are becoming routine. Yet, the frequency at which live cloned offspring are produced remains below 5%, irrespective of the nuclear donor species or cell type. One possible explanation is that the reprogramming factor(s) of each oocyte is insufficient or not properly adapted for the receipt of a somatic cell nucleus, because it is naturally prepared only for the receipt of a gamete. Here, we have increased the oocyte volume by oocyte fusion and examined its subsequent development. We constructed oocytes with volumes two to nine times greater than the normal volume by the electrofusion or mechanical fusion of intact and enucleated oocytes. We examined their in vitro and in vivo developmental potential after parthenogenetic activation, intracytoplasmic sperm injection (ICSI) and somatic cell nuclear transfer (SCNT). When the fused oocytes were activated parthenogenetically, most developed to morulae or blastocysts, regardless of their original size. Diploid fused oocytes were fertilized by ICSI and developed normally and after embryo transfer, we obtained 12 (4-15%) healthy and fertile offspring. However, enucleated fused oocytes could not support the development of mice cloned by SCNT. These results suggest that double fused oocytes have normal potential for development after fertilization, but oocytes with extra cytoplasm do not have enhanced reprogramming potential.

Growth retardation of inner cell mass cells in polyspermic porcine embryos produced in vitro

The in vitro viability of polyspermic pig eggs was investigated. Immature oocytes were matured and fertilized in vitro. Approximately 10 h after insemination, the eggs were centrifuged at 12 000 x g for 10 min and individually classified into two (2PN)- and poly-pronuclear (PPN, 3 or 4 pronuclei) eggs. The classified eggs were cultured in vitro or in vivo. Nuclei numbers of inner cell mass (ICM) and trophectoderm (TE) were compared between 2PN- and PPN-derived blastocysts. The frequency of development in vitro of 2PN and PPN eggs to the blastocyst stage was 53.6% and 40.7%, respectively. The mean number (8.2 +/- 0.7, n = 48) of ICM nuclei of 2PN-derived blastocysts was higher than that (4.2 +/- 0.8, n = 37) of PPN-derived blastocysts (p < 0.001), whereas there was no difference (p > 0.05) in mean numbers of total (46.7 +/- 3.4 vs. 39. 9 +/- 3.9) and TE nuclei (38.5 +/- 2.9 vs. 35.7 +/- 3.3) between the two groups. Development of 2PN and PPN eggs cultured in vivo to the blastocyst stage was 33.3% and 27.4%, respectively. The numbers of ICM and TE nuclei of these embryos cultured in vivo showed a pattern similar to that for the in vitro-produced blastocysts. Additionally, fetuses were obtained on Day 21 from both the 2PN and the PPN groups. This suggests that polyspermic pig embryos develop to the blastocyst stage and beyond, although showing a smaller ICM cell number as compared to normal embryos.

DNA ploidy abnormalities in rabbit preimplantation embryos are not increased by conditions associated with in vitro culture

Possible adverse effects of in vitro culture-associated physical factors were studied in 3- and 4-day-old rabbit embryos. Laboratory conditions were mimicked by exposure to visible light (320-740 nm, 1600 lx) or decreased temperature (22 +/- 1 degree C). Embryos were exposed for a 24-hr period followed by either immediate evaluation or an additional 24 hr of standard in vitro culture (darkness, 37 degrees C) and evaluation thereafter. Effects were assayed by cytophotometric measurement of the DNA content in Feulgen-stained cell nuclei and by cell number. The incidence of DNA aneuploid embryos and DNA aneuploid cell nuclei per embryo, as well as the average nuclear DNA content, was not significantly different between exposed embryos and controls. Both in vitro culture and reduced temperature caused a decrease in cell number. The temperature-induced cell number decrease was reversible within 24 hr after return to 37 degrees C. These results demonstrate that physical factors associated with in vitro culture do not increase DNA ploidy abnormalities in cultured preimplantation embryos.