Mouse endogenous X-linked genes do not show lineage-specific delayed inactivation during development

Abstract

SummaryX chromosome inactivation (XCI) has been assumed to be complete in all cells of female mouse embryos at about 6 d post coitum (dpc). However, a recent study on β-galactosidase expression of an X-linkedlacZtransgene suggests that XCI is probably not complete several days after this time in some lineages. To help resolve this issue, we analysed XCI in embryos which carry the T(X;16)16H (Searle's) translocation and are heterozygous at the X-linkedHprtandPgk-1genes. The quantitative RT-PCR single nucleotide primer extension (SNuPE) assay was used to measureHprtandPgk-1allele-specific transcripts in embryos 9·5 dpc. No transcripts from the normal X chromosome were found in any of the tissues tested, indicating that inactivation was complete for these endogenous genes.