Histone modifications at the blastocyst Axin1(Fu) locus mark the heritability of in vitro culture-induced epigenetic alterations in mice.

For epigenetic phenotypes to be passed on from one generation to the next, it is required that epigenetic marks between generations are not cleared during the two stages of epigenetic reprogramming: mammalian gametogenesis and preimplantation development. The molecular nature of the chromatin marks involved in these events is unknown. Using the epigenetically inherited allele Axin1(Fu) (the result of a retrotransposon insertion upstream of the Axin1 gene) we sought to establish the heritable mark during early embryonic development that determines transgenerational epigenetic inheritance and to examine a possible shift in the expression of this epiallele in future progeny induced by in vitro culture (IVC). To identify the heritable mark we analyzed 1) the level of DNA methylation shown by the Axin1(Fu) allele in sperm and embryos at blastocysts stage and 2) the histone marks (H3K4 me2, H3K9 me3, H3K9 ac, and H4K20 me3) present at the blastocyst stage at the specific Axin1(Fu) locus. According to our data, histone H3K4 me2 and H3K9 ac mark the differences between the Axin1(Fu) penetrant and the silent locus during the first period of demethylation of the preimplantation development. Moreover, suboptimal IVC (reported to produce epigenetic alterations in embryos) and the histone deacetylase inhibitor trichostatin A affect the postnatal expression of this epigenetically sensitive allele through histone modifications during early development. This finding indicates that altered histone modifications during preimplantation can drive altered gene expression later on in development.