Physiological functions of the imprinted Gnas locus and its protein variants Gαs and XLαs in human and mouse

The stimulatory alpha-subunit of trimeric G-proteins G alpha(s) which upon ligand binding to seven-transmembrane ran e receptors activates adenylyl cyclases to produce the second messenger cAMP constitutes one of the archetypal signal transduction molecules that have beer) studied in much detail. Over the past few years, however, genetic as well as biochemical approaches have led to a range of novel insights into the G alpha(s) encoding guanine nucleotide binding protein, alpha-stimulating (Gnas) locus, its alternative protein products and its regulation by genomic imprinting, which leads to monoallelic, parental origin-dependent expression of the various transcripts. Here, we summarise the major characteristics of this complex gene locus and describe the physiological roles of G alpha(s) and its 'extra large' variant XL alpha(s) at post-natal and adult stages as defined by genetic mutations. Opposite and potentially antagonistic functions of the two proteins in the regulation of energy homeostasis and metabolism have been identified in Gnas- and Gnasxl (XL alpha(s))-deficient mice, which are characterised by obesity and leanness respectively. A comparison of findings in mice with symptoms of the corresponding human genetic disease 'Albright's hereditary osteodystrophy' / 'pseudohypoparathyroidism' indicates highly conserved functions as well as unresolved phenotypic differences.