In vitro analysis of pre- and early postimplantation development of lethal yellow (Ay/Ay) mouse embryos

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Abstract
Preimplantation embryos from matings between yellow heterozygous (Ay/a) mice were recovered at 56 hours post coitum, cultured for five days, and compared with the development of embryos from three control matings (Ay/a ♀ × a/a ♂, a/a ♀ × Ay/a ♂, a/a ♀ × a/a ♂). Most embryos were at the 8‐cell stage at recovery; however fewer embryos from the experimental cross had developed to the 8‐cell stage than embryos of control matings, indicating a developmental lag of experimental embryos (P < 0.01). The yellow (Ay/a) uterus did not contribute (P = 0.05) to delayed development. Experimental and control embryos were equally capable of successful development in culture to the morula stage with no distinct morphological characteristics identifying the class of Ay/Ay mutants. However, significant differences were observed in the development from morulae to blastocysts; 9.4% (10/106) of the morulae in experimental crosses failed to undergo blastocyst formation as compared with 2.5% (10/398) of morulae in pooled control crosses (P = 0.010–0.025). In the experimental cross 25.0% (24/96) of embryos that developed successfully to the blastocyst stage failed to hatch from the zona pellucida; these are presumed to include the class of lethal yellow homozygotes. Abnormalities seen in cultured embryos consisted primarily of blastomere disintegration, blastomere arrest and exclusion, and embryo fragmentation.