International Mammalian Genome Society

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

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A4 Methylation is Acquired at Different Times on the Maternal and Paternal H19 Alleles During Male Germ Cell Development

Tamara L. Davis1, Grace J.Yang1, John McCarrey2 and Marisa S. Bartolomei1. 1HHMI and Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA; 2Southwest Foundation for Biomedical Research, San Antonio, Texas

A subset of mammalian genes are subject to parent of origin-specific expression. Such genes are termed imprinted based on the fact that the maternal and paternal alleles must be differently marked to allow parental origin to be distinguished and expression regulated appropriately. To date, DNA methylation is the leading candidate for the imprinting mark. It is believed that imprints must be set in the germline since this is when the maternal and paternal genomes are separate. In support of this hypothesis, the paternal-specific methylation at the murine H19 locus is inherited from sperm and is absent in oocytes.

To determine when imprints are established during germ cell development, we have analyzed the status of methylation at the H19 locus during gametogenesis. We found that methylation is erased from the paternal H19 allele in 13.5 dpc female primordial germ cells. This result suggests that the maternal pattern of hypomethylation at H19 is present in female germ cells as early as midgestation. Establishment of the paternal pattern of hypermethylation in the male germline is more complex. 13.5 dpc male primordial germ cells lack methylation on both the maternal and the paternal H19 alleles, indicating that during male germ cell development, the paternal-specific methylation inherited from sperm is erased. By embryonic day 15.5, the paternal H19 allele is methylated in prospermatogonia. In contrast, the maternal H19 allele does not acquire significant methylation until the primitive type A spermatogonia appear at 6 days post partum. Therefore, the maternal and paternal alleles of H19 remain distinct in the male germline despite the fact that methylation differences do not persist throughout gametogenesis.


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