International Mammalian Genome Society

The 13th International Mouse Genome Conference
October 31-November 3, 1999

Table of Contents * Structure * Bioinformatics * Sequence * Mapping * New Tools * Gene Discovery * Developmental * Mutagenesis * Functional Genomics

A13 Regulation of Imprinted Gene Expression in the Preimplantation Embryo

Mellissa Mann, Adam Doherty, Kim Tremblay, Richard Schultz and Marisa Bartolomei. Howard Hughes Medical Institute, University of Pennsylvania, School of Medicine, Philadelphia, PA

Genomic imprinting is defined as an epigenetic modification of parental alleles such that only one is expressed. For imprinted genes to be expressed appropriately, the imprinting marks carried by sperm and oocyte DNA must be maintained in the developing embryo. The period of preimplantation development is a time of dynamic epigenetic changes. Very little is known about the mechanism involved in interpreting and maintaining these germ-line imprints during this dynamic period. The aim of this research is to determine whether imprinting may be perturbed in the preimplantation embryo. To this end, parental-allele specific expression of the imprinted H19 gene was examined after culture of embryos to the blastocyst stage in different media. Two culture media were used in this analysis, the computer-optimized medium, KSOM and amino acids, and the commonly used but suboptimal medium, Whitten's. Embryos were recovered at the 2-cell stage and cultured in Whitten's or KSOM media until they reached the blastocyst stage. Embryos were then assayed for allele-specific expression. Culture of preimplantation embryos in KSOM and amino acids maintained the imprinted expression of H19, similar to control embryos, although a small fraction of the transcripts were paternally derived. In contrast, Whitten's medium failed to maintain appropriate imprinted expression, since H19 was expressed from both the maternal and paternal alleles. To determine whether a more global deregulation of imprinted gene expression occurs upon culture, Snrpn was analyzed for parental allele-specific expression. Unlike H19, preimplantation embryos cultured in Whitten's medium and in KSOM plus amino acids maintained strict monoallelic expression of Snrpn. No maternal Snrpn expression was observed. These results indicate that not all imprinted genes undergo deregulated expression, possibly suggesting that at least at some level the imprinting mechanisms controlling the expression of these genes are distinct. Studies to investigate how deregulated expression of H19 occurs at the molecular level are being pursued.


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