Use of a HpaII-polymerase chain reaction assay to study DNA methylation in the Pgk-1 CpG island of mouse embryos at the time of X-chromosome inactivation.

A HpaII-PCR assay was used to study DNA methylation in individual mouse embryos. It was found that HpaII site H-7 in the CpG island of the X-chromosome-linked Pgk-1 gene is less than or equal to 10% methylated in oocytes and male embryos but becomes 40% methylated in female embryos at 6.5 days; about the time of X-chromosome inactivation of the inner cell mass.