Marisa Bartolomei
Department of Cell and Developmental Biology; University of Pennsylvania School of Medicine
Preimplantation development is a period of dynamic epigenetic change that begins with remodeling of the egg and sperm genomes, and ends with implantation. During this time, parental-specific imprinting marks must be established and maintained. These marks direct the parental-allele-specific expression patterns of a small number of genes in mammals, including the maternally-expressed H19 gene and the paternally-expressed Snrpn gene. We and others have previously demonstrated that H19 imprinting can be perturbed during preimplantation development (1, 2, 4). To define the lability of genomic imprints during this dynamic period and to determine whether loss of imprinting continues at later stages of development, imprinted gene expression and methylation were examined after in vitro preimplantation culture (3). Following culture of 2-cell embryos to the blastocyst stage, the normally silent paternal H19 allele was aberrantly expressed. Loss of imprinting persisted in midgestation conceptuses: placental tissue displayed loss of imprinting for multiple imprinted genes while imprinting was generally preserved in the corresponding embryos. Loss of imprinted expression was associated with loss of methylation at the H19 and Snrpn imprinting controls regions. These results indicate that genomic imprints are labile during preimplantation development and loss of imprinting can persist, at least in tissues of trophectodermal origin. Work is in progress to determine which aspect(s) of preimplantation culture determine future epigenetic dysregulation. Finally, these results provide a strong cautionary note for the culture of human embryos and cells since the effect of suboptimal culture on epigenetic information in humans is not known. (Supported by the NIH (HD42026), Howard Hughes Medical Institute and Lalor Foundation.)
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