Research for the transcriptional regulation of Gsα protein gene

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The transcriptional regulation of Gsα gene (GNAS1) is under control of genetic and epigenetic mechanism and subjects to tissue-specific genomic imprinting. In order to clarify this mechanism, the experimental and clinical study was performed Allele-specific expression of GNAS1 mRNA was studied by RT-PCR using cultured tubular cells isolated from human urine which were considered to be proximal tubule origin. Despite both normal and abnormal methylation patterns in the promoter region, mRNA of Gsα protein was biallelically expressed in these cells, therefore tissue-specific genomic imprinting requires both DNA methylation in GNAS1 and other trans-acting factors produced in highly differentiated status. In all 14 cases with sporadic pseudohypoparathyroidism type Ib (PHP-Ib), the maternal methylation pattern was lost in three promoter regions (NESP55, AS, exon1A) of GNAS1 and the methylation pattern in XLas region was different in each case. Among these cases, eight showed loss of methylation in all sites in XLas region examined by Southern hybridization and included four cases with some specific clinical features like mental retardation. Methylation status of each CpG site in 5' and 3' flanking region of exon XL was examined by bisulfite PCR No specific methylation pattern for clinical features was shown and loss of allelic contiguity in CpG methylation was observed in PHP-Ib. These results suggest that the epigenetic abnormality in other region is responsible for the abnormal methylation pattern in XLas region.