Studies of the regulation and function of the G sα gene Gnas using gene targeting technology

Metabolic Diseases Branch, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, Bethesda, MD 20854, USA.
Pharmacology [?] Therapeutics (Impact Factor: 9.72). 08/2007; 115(2):271-291. DOI: 10.1016/j.pharmthera.2007.03.013
Source: PubMed


The heterotrimeric G protein α-subunit Gsα is ubiquitously expressed and mediates receptor-stimulated intracellular cAMP generation. Its gene Gnas is a complex imprinted gene which uses alternative promoters and first exons to generate other gene products, including the Gsα isoform XLαs and the chromogranin-like protein NESP55, which are specifically expressed from the paternal and maternal alleles, respectively. Gsα itself is imprinted in a tissue-specific manner, being biallelically expressed in most tissues but paternally silenced in a few tissues. Gene targeting of specific Gnas transcripts demonstrates that heterozygous mutation of Gsα on the maternal (but not the paternal) allele leads to early lethality, perinatal subcutaneous edema, severe obesity, and multihormone resistance, while the paternal mutation leads to only mild obesity and insulin resistance. These parent-of-origin differences are the consequence of tissue-specific Gsα imprinting. XLαs deficiency leads to a perinatal suckling defect and a lean phenotype with increased insulin sensitivity. The opposite metabolic effects of Gsα and XLαs deficiency are associated with decreased and increased sympathetic nervous system activity, respectively. NESP55 deficiency has no metabolic consequences. Other gene targeting experiments have shown Gnas to have 2 independent imprinting domains controlled by 2 different imprinting control regions. Tissue-specific Gsα knockout models have identified important roles for Gsα signaling pathways in skeletal development, renal function, and glucose and lipid metabolism. Our present knowledge gleaned from various Gnas gene targeting models are discussed in relation to the pathogenesis of human disorders with mutation or abnormal imprinting of the human orthologue GNAS.

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    • "Although G s α is expressed in liver, adipose tissue, pancreatic islets and muscle, these tissues are not involved in the parent-of-origins effects of G s α mutations as G s α expression is not affected by imprinting in these tissues (Germain-Lee et al., 2005; Mantovani et al., 2004; Weinstein et al., 2007; Yu et al., 2000; Yu et al., 1998) and G s α knockouts in these tissues due not produce a phenotype similar to the germline maternal G s α knockout (Chen et al., 2010; Chen et al., 2009a; Chen et al., 2005b; Xie et al., 2010; Xie et al., 2007). However studies of mice with disruption of either the maternal or paternal G s α allele in the central nervous system (mBrGsKO and pBrGsKO mice, respectively) that were generated by reciprocal matings of Nestin-cre and G s α-floxed mice indicate that G s α imprinting in the central nervous system underlies the parent-of-origin effects of G s α mutations on energy and glucose metabolism (Chen et al., 2009b). "
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    ABSTRACT: G(s)α is a ubiquitously expressed G protein α-subunit that couples receptors to the generation of intracellular cyclic AMP. The G(s)α gene GNAS is a complex gene that undergoes genomic imprinting, an epigenetic phenomenon that leads to differential expression from the two parental alleles. G(s)α is imprinted in a tissue-specific manner, being expressed primarily from the maternal allele in a small number of tissues. Albright hereditary osteodystrophy is a monogenic obesity disorder caused by heterozygous G(s)α mutations but only when the mutations are maternally inherited. Studies in mice indicate a similar parent-of-origin effect on energy and glucose metabolism, with maternal but not paternal mutations leading to obesity, reduced sympathetic nerve activity and energy expenditure, glucose intolerance and insulin resistance, with no primary effect on food intake. These effects result from G(s)α imprinting leading to severe G(s)α deficiency in one or more regions of the central nervous system, and are associated with a specific defect in melanocortins to stimulate sympathetic nerve activity and energy expenditure.
    European journal of pharmacology 06/2011; 660(1):119-24. DOI:10.1016/j.ejphar.2010.10.105 · 2.53 Impact Factor
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    • "The human GNAS gene is located on chromosome 20q13.2-13.3 and expression of GNAS products is regulated both by imprinting and alternative splicing (Weinstein et al., 2007). Usage of alternative promoters and first exons that splice onto a common exon (exon 2) results in multiple gene products. "
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    ABSTRACT: The human GNAS gene is imprinted in a tissue-specific manner, being expressed primarily from the maternal allele in pituitary, thyroid, renal proximal tubules, and gonads, but is supposed to be biallelically expressed with an equal allelic expression in most other tissues. We analysed allelic expression of Gαs using Pyrosequencing. By genotyping the GNAS T393C polymorphism we quantified mRNA transcripts in lymphoblasts (Ly, n=11), peripheral blood mononuclear cells (PBMC, n=18), mammary adipose tissue (MAT, n=23) and heart tissue (HT, n=44). Allelic expression analysis revealed an unequal allelic expression (ratio maternal/total×100±SEM: 55.7±1% (95% CI 53.4-58.1%) in Ly, 56.1±0.8 (95% CI 54.5-57.7%) in PBMC, 54.5±0.8% (95% CI 53-56.1%) in MAT and 54.1±0.6% (95% CI 53-55.3%) in HT). Maternal ratio differed significantly from the mean (p<0.0001). This phenomenon may be a general feature existing in all tissues.
    Molecular and Cellular Endocrinology 06/2011; 341(1-2):63-70. DOI:10.1016/j.mce.2011.05.032 · 4.41 Impact Factor
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    • "One such cluster of imprinted genes is the mammalian GNAS domain which consists of a number of imprinted genes which display complex transcriptional and epigenetic regulation [12,13]. In humans, the GNAS domain spans ~70 kilobases (kb) on chromosome 20 and displays similar gene organisation and imprinting patterns to the orthologous Gnas domain on murine chromosome 2 [14]. An integral member of this domain is the GNAS gene which encodes the alpha-stimulatory subunit of the trimeric guanine nucleotide-binding (or G-protein, GSα). "
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    ABSTRACT: Genes which are epigenetically regulated via genomic imprinting can be potential targets for artificial selection during animal breeding. Indeed, imprinted loci have been shown to underlie some important quantitative traits in domestic mammals, most notably muscle mass and fat deposition. In this candidate gene study, we have identified novel associations between six validated single nucleotide polymorphisms (SNPs) spanning a 97.6 kb region within the bovine guanine nucleotide-binding protein Gs subunit alpha gene (GNAS) domain on bovine chromosome 13 and genetic merit for a range of performance traits in 848 progeny-tested Holstein-Friesian sires. The mammalian GNAS domain consists of a number of reciprocally-imprinted, alternatively-spliced genes which can play a major role in growth, development and disease in mice and humans. Based on the current annotation of the bovine GNAS domain, four of the SNPs analysed (rs43101491, rs43101493, rs43101485 and rs43101486) were located upstream of the GNAS gene, while one SNP (rs41694646) was located in the second intron of the GNAS gene. The final SNP (rs41694656) was located in the first exon of transcripts encoding the putative bovine neuroendocrine-specific protein NESP55, resulting in an aspartic acid-to-asparagine amino acid substitution at amino acid position 192. SNP genotype-phenotype association analyses indicate that the single intronic GNAS SNP (rs41694646) is associated (P ≤ 0.05) with a range of performance traits including milk yield, milk protein yield, the content of fat and protein in milk, culled cow carcass weight and progeny carcass conformation, measures of animal body size, direct calving difficulty (i.e. difficulty in calving due to the size of the calf) and gestation length. Association (P ≤ 0.01) with direct calving difficulty (i.e. due to calf size) and maternal calving difficulty (i.e. due to the maternal pelvic width size) was also observed at the rs43101491 SNP. Following adjustment for multiple-testing, significant association (q ≤ 0.05) remained between the rs41694646 SNP and four traits (animal stature, body depth, direct calving difficulty and milk yield) only. Notably, the single SNP in the bovine NESP55 gene (rs41694656) was associated (P ≤ 0.01) with somatic cell count--an often-cited indicator of resistance to mastitis and overall health status of the mammary system--and previous studies have demonstrated that the chromosomal region to where the GNAS domain maps underlies an important quantitative trait locus for this trait. This association, however, was not significant after adjustment for multiple testing. The three remaining SNPs assayed were not associated with any of the performance traits analysed in this study. Analysis of all pairwise linkage disequilibrium (r2) values suggests that most allele substitution effects for the assayed SNPs observed are independent. Finally, the polymorphic coding SNP in the putative bovine NESP55 gene was used to test the imprinting status of this gene across a range of foetal bovine tissues. Previous studies in other mammalian species have shown that DNA sequence variation within the imprinted GNAS gene cluster contributes to several physiological and metabolic disorders, including obesity in humans and mice. Similarly, the results presented here indicate an important role for the imprinted GNAS cluster in underlying complex performance traits in cattle such as animal growth, calving, fertility and health. These findings suggest that GNAS domain-associated polymorphisms may serve as important genetic markers for future livestock breeding programs and support previous studies that candidate imprinted loci may act as molecular targets for the genetic improvement of agricultural populations. In addition, we present new evidence that the bovine NESP55 gene is epigenetically regulated as a maternally expressed imprinted gene in placental and intestinal tissues from 8-10 week old bovine foetuses.
    BMC Genetics 01/2011; 12(1):4. DOI:10.1186/1471-2156-12-4 · 2.40 Impact Factor
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