50% of the levels seen in wild-type littermates [40]. Similar findings have been reported recently in mice heterozygous for either paternal or maternal disruption of Gnas exon 1, and these studies additionally demonstrated that Gsα expression is also predominantly maternal in the thyroid [41]. Consistent with these findings, the active maternal Gsα promoter shows a greater ratio of tri- to dimethylated histone-3 Lys4 compared to the silenced paternal promoter in the proximal tubule, whereas the amount of methylated histones is similar in maternal and paternal Gsα promoters in liver, a tissue in which Gsα is biallelic [42].
