Analysis of the sex ratio in preimplantation embryos from B6.K1 and B6.K2 Ped gene congenic mice

Collection and preparation of rodent embryonic samples for transcriptome study

The need for large-scale collection of rodent embryos and individual embryonic tissues for genomic and proteomic studies requires modification of traditional practices of embryo necropsy. The sample intended for transcriptome study should be rapidly dissected and stabilized to preserve its molecular integrity. The retrieval of high-quality RNA, DNA, and proteins from the target tissue is crucial for informative molecular analysis (e.g., gene profiling on microarray platform). We present a reliable method of collection and preparation of rodent embryos for genomic studies supported by detailed protocols and RNA extraction results for different stages of mouse embryonic development.

Loss of genomic imprinting in mouse embryos with fast rates of preimplantation development in culture

Currently, the stage of embryo development has been proposed as one of many criteria for identifying healthy embryos in infertility clinics with the fastest embryos being highlighted as the healthiest. However the validity of this as an accurate criterion with respect to genomic imprinting is unknown. Given that embryo development in culture generally requires an extra day compared to in vivo development, we hypothesized that loss of imprinting correlates with slower rates of embryonic development. To evaluate this, embryos were recovered at the 2-cell stage, separated into four groups based on morphological stage at two predetermined time points, and cultured to blastocysts. We examined cell number, embryo volume, embryo sex, imprinted Snrpn and H19 methylation, imprinted Snrpn, H19, and Cdkn1c expression, and expression of genes involved in embryo metabolism-Atp1a1, Slc2a1, and Mapk14-all within the same individual embryo. Contrary to our hypothesis, we observed that faster developing embryos exhibited greater cell numbers and embryo volumes as well as greater perturbations in genomic imprinting and metabolic marker expression. Embryos with slower rates of preimplantation development were most similar to in vivo derived embryos, displaying similar cell numbers, embryo volumes, Snrpn and H19 imprinted methylation, H19 imprinted expression, and Atp1a1 and Slc2a1 expression. We conclude that faster development rates in vitro are correlated with loss of genomic imprinting and aberrant metabolic marker expression. Importantly, we identified a subset of in vitro cultured embryos that, according to the parameters evaluated, are very similar to in vivo derived embryos and thus are likely most suitable for embryo transfer.