Building a better mouse embryo assay: effects of mouse strain and in vitro maturation on sensitivity to contaminants of the culture environment.

PURPOSE: The aim of this study is to compare the sensitivity of the standard one-cell mouse embryo assay (MEA) to that using in vitro-matured oocytes from hybrid and outbred mice. METHODS: The study was done by culturing embryos in the presence or absence of two concentrations (0.0005 or 0.001 % v/v) of Triton X-100 (TX100). Embryonic development, blastocyst cell numbers (total and allocation to the trophectoderm [TE] and inner cell mass [ICM]), and blastocyst gene expression were evaluated. RESULTS: Neither concentration of TX100 affected (P > 0.05) cleavage, blastocyst development, or hatching in one-cell embryos from BDF1 mice. However, all cell number endpoints were reduced (P < 0.05) by the high concentration of TX100 and the number of ICM cells was reduced (P < 0.05) by the low concentration of TX100. Inhibitory (P < 0.05) effects of the high concentration of TX100 were observed in in vitro maturation (IVM) embryos from BDF1, CF1, and SW, but not ICR, mice. Cell number and allocation were negatively affected by the high concentration of TX100 in CF1 and SW embryos, but not in BDF1 or ICR embryos. The only developmental endpoints affected by the low concentration of TX100 were cleavage of BDF1 oocytes, blastocyst development of SW embryos, and cell numbers (total and inner cell mass (ICM)) of SW blastocysts. CONCLUSIONS: The sensitivity of the MEA to TX100 is improved by using embryos from in vitro-matured oocytes, using oocytes from some outbred (SW or CF1, not ICR) strains of mice, and evaluating blastocyst cell number and allocation.

The beneficial effects of reduced magnesium during the oocyte-to-embryo transition are conserved in mice, domestic cats and humans.

In many cell types Mg2+ can antagonise Ca2+ -stimulated signalling pathways, but information regarding the effects of these ions on IVF and subsequent embryonic development is limited. Our objectives were to evaluate the effects of Mg2+ in the IVF medium on embryonic development in mice and then determine if similar effects occurred in domestic cats and humans. Oocytes from hybrid and outbred mice, domestic cats and humans were fertilised (IVF, mice and cats; intracytoplasmic sperm injection (ICSI), humans) in the presence of 0.2 or 1.2 (mouse and human) or 1.0 (cat) mM Mg2+ and the resulting embryos were cultured to the blastocyst stage. Decreased concentrations of Mg2+ during IVF increased (P<0.05) cleavage of oocytes from outbred mice (77.9 vs. 51.0%), development of embryos from hybrid mice (74.5 vs. 51.0% hatching blastocyst per cleaved embryo) and both cleavage (68.4 vs. 46.8%) and blastocyst development (53.0 vs. 26.2% per cleaved embryo) in cats. Development to the blastocyst stage (52.1 vs. 40.2%) was also improved (P<0.05) when ICSI was performed on human oocytes in the presence of 0.2 mM Mg2+, compared with a commercial culture medium. Sensitivity to increased (1.0 to 1.2 mM) concentrations of Mg2+ in the medium during the oocyte-to-embryo transition appears to be conserved in three different species.