COORDINATE CONTROL AND VARIATION IN X-LINKED GENE-EXPRESSION AMONG FEMALE MICE

In normal female mammals, one of the two X Chromosome (Chr) homologs p er cell is silenced coordinately during early embryogenesis. The genes located on the inactivated X homolog are predicted to be influenced b y the same underlying repression mechanism. To test the uniformity of cis-acting gene repression, 32 genetically identical F-1 female mice w ere analyzed for differential expression of homologous alleles at thre e X-linked genes-Otc, Atp7a (=Mottled), and Hprt. Gene expression was assayed by the single-nucleotide primer extension (SNuPE) method, ther eby allowing the three genes to be quantitated from the same RNA sampl e. Although variable between individual animals, the relative expressi on of the two alleles (allelic expression ratio) of the genes is signi ficantly correlated within each steady-state RNA pool. When examined b y animal age (3 months to 12 months), no statistically significant dif ferences were observed in the mean or variance of allelic expression r atio. Together, the results confirm that X inactivation is coordinatel y controlled and is stable across the early- to mid-adult life span.