Reactivation of hprt on the inactive X chromosome with DNA demethylating agents
Hockey, A.J.; Adra, C.N.; McBurney, M.W.
Somatic Cell and Molecular Genetics 15(5): 421-434
ISSN/ISBN: 0740-7750 PMID: 2476861 DOI: 10.1007/bf01534893
The C86 line of female embryonal carcinoma cells contains one active and one inactive X chromosome. Following methylnitrosourea mutagenesis, a clone called C86AGM2 was isolated that carries a mutated hprt gene on the active X chromosome. This hprtm allele encodes an HPRT enzyme that has less than 1% normal enzyme activity, is thermolabile, and has an altered isoelectric point. Following treatment with drugs that demethylate DNA, the hprt+ gene from the inactive X chromosome in C86AGM2 cells became active as determined by the appearance of HPRT activity with the thermodenaturation and electrofocusing characteristics of the normal enzyme. No expression of this hprt+ gene occurred if C86AGM2 cells were induced to differentiate prior to DNA demethylation. Stable lines of C86AGM2 cells expressing both the hprtm and hprt+ genes did not inactivate either gene following differentiation.