Improved DNA methylation analysis via enrichment of demethylated cells expressing an X-inactivated GFP transgene. Mus musculus

The demethylating drug 5-aza-2’-deoxycytidine (5-aza-2dC) is frequently used to investigate the effect of global DNA demethylation on gene expression in cultured mammalian cells. Here, we utilize a novel method that uses the reactivation of an X-inactivated GFP transgene as a marker to enrich for cells that have undergone drug-induced demethylation. By combining it with microarray gene expression profiling, we demonstrate the method’s utility in identifying genes activated by global DNA demethylation. Keywords: 5-aza-2'-deoxycytidine; methylation; dermal fibroblast; X-linked GFP Overall design: Mice used have an X-linked GFP transgene driven by the chicken β-actin promoter and CMV intermediate early enhancer in a 129/ICR mixed genetic background obtained from The Jackson Laboratory. Male transgenic animals were bred to wildtype BL6 female mice to obtain females that were heterozygous for the transgene. Dermal fibroblasts were obtained from explant cultures of neonatal female mice from these crosses. The cells were then sorted using FACS to obtain only GFP-nonexpressing cells. These cells represent the population with the GFP transgene on the inactive X chromosome. The GFP-silent cells were treated with the demethylating drug 5-aza-2'-deoxycytidine. This drug does not affect all cells and uses a passive form of demethylation that results in a heterogenous population of unaffected and demethylated cells. A portion of the cells affected by demethylation activate the inactive GFP transgene by demethylating the inactive X chromosome. The GFP-active and GFP-inactive cells were sorted by FACS and assayed by microarray to determine what genes were affected by demethylation. Also the microarray results indicated if sorting for GFP-active cells enriches for cells affected by the drug.