Comparative analysis of DNA methylation in transgenic mice with unstable CGG repeats from FMR1 gene.

Methylation of CpG sequences in and around CGG triplet repeats in FMR1 gene has strong correlation with manifestation of the fragile X syndrome in human patients. In contrast, we have observed a lack of correlation between repeat instability and DNA methylation in three different transgenic mouse models harboring unstable CGG repeats. Further we have demonstrated that the endogenous copy of mouse Fmr1 gene remains unmethylated both in males and females.

Instability of CGG repeats in transgenic mice.

Dynamic mutation resulting in the expansion of CGG repeats in the untranslated region (UTR) of the first exon of the FMR1 gene in humans results in fragile X syndrome. Long stretches of CGG repeats that are known to be highly unstable in humans have so far failed to show similar intergenerational instability in transgenic mice. We generated transgenic lines that show a dramatic increase from 26 to >300 repeats in three generations.