The stimulatory G protein alpha-subunit G(s)alpha couples receptors to adenylyl cyclase and is required for hormone-stimulated cAMP generation. In Albright hereditary osteodystrophy, heterozygous G(s)alpha null mutations only lead to PTH, TSH, and gonadotropin resistance when inherited maternally [pseudohypoparathyroidism type 1A; (PHP1A)]. Maternal-specific expression of G(s)alpha in specific hormone targets could explain this observation. Using hot-stop PCR analysis on total RNA from six normal human thyroid specimens, we showed that the majority of the G(s)alpha mRNA (72 +/- 3%) was derived from the maternal allele. This is consistent with the presence of TSH resistance in patients with maternal G(s)alpha null mutations (PHP1A) and the absence of TSH resistance in patients with paternal G(s)alpha mutations (pseudopseudohypoparathyroidism). Patients with PTH resistance in the absence of Albright hereditary osteodystrophy (PHP1B) have an imprinting defect of the G(s)alpha gene resulting in both alleles having a paternal epigenotype, which would lead to a more moderate level of thyroid-specific G(s)alpha deficiency. We found evidence of borderline TSH resistance in 10 of 22 PHP1B patients. This study provides further evidence for tissue-specific imprinting of G(s)alpha in humans and provides a potential mechanism for mild to moderate TSH resistance in PHP1A and borderline resistance in some patients with PHP1B.
Gnas is a complex gene with multiple imprinted promoters. The upstream Nesp and Nespas͞Gnasxl promoters are paternally and maternally methylated, respectively. The downstream promoter for the stimulatory G protein ␣-subunit (Gs␣) is unmethylated, although in some tissues (e.g., renal proximal tubules), G s␣ is poorly expressed from the paternal allele. Just upstream of the Gs␣ promoter is a primary imprint mark (1A region) where maternalspecific methylation is established during oogenesis. Pseudohypoparathyroidism type 1B, a disorder of renal parathyroid hormone resistance, is associated with loss of 1A methylation. Analysis of embryos of Dnmt3L ؊/؊ mothers (which cannot methylate maternal imprint marks) showed that Nesp, Nespas͞Gnasxl, and 1A imprinting depend on one or more maternal primary imprint marks. We generated mice with deletion of the 1A differentially methylated region. These mice had normal Nesp-Nespas͞Gnasxl imprinting, indicating that the Gnas locus contains two independent imprinting domains (Nespas-Nespas͞Gnasxl and 1A-G s␣) controlled by distinct maternal primary imprint marks. Paternal, but not maternal, 1A deletion resulted in Gs␣ overexpression in proximal tubules and evidence for increased parathyroid hormone sensitivity but had no effect on G s␣ expression in other tissues where Gs␣ is normally not imprinted. The 1A region is a maternal imprint mark that contains one or more methylation-sensitive cis-acting elements that suppress Gs␣ expression from the paternal allele in a tissue-specific manner.genomic imprinting ͉ pseudohypoparathyroidism ͉ DNA methylation ͉ guanine nucleotide binding protein
Alcohols and volatile anesthetics enhance the function of inhibitory glycine receptors (GlyRs). This is hypothesized to occur by their binding to a pocket formed between the transmembrane domains of individual ␣1 GlyR subunits. Because GlyRs are pentameric, it follows that each GlyR contains up to five alcohol/anesthetic binding sites, with one in each subunit. We asked how many subunits per pentamer need be bound by drug in order to enhance receptormediated currents. A cysteine mutation was introduced at amino acid serine 267 (S267C) in the transmembrane 2 domain as a tool to block GlyR potentiation by some anesthetic drugs and to provide a means for covalent binding by the small, anesthetic-like thiol reagent propyl methanethiosulfonate. Xenopus laevis oocytes were coinjected with various ratios of wild-type (wt) to S267C ␣1 GlyR cDNAs in order to express heteromeric receptors with a range of wt:mutant subunit stoichiometries. The enhancement of GlyR currents by 200 mM ethanol and 1.5 mM chloroform was positively correlated with the number of wt subunits found in heteromeric receptors. Furthermore, currents from oocytes injected with high ratios of wt to S267C cDNAs (up to 200:1) were significantly and irreversibly enhanced following propyl methanethiosulfonate labeling and washout, demonstrating that drug binding to a single subunit in the receptor pentamer is sufficient to induce enhancement of GlyR currents.Although volatile anesthetics were long believed to have nonspecific, lipid-based mechanisms of action, accumulating evidence led to a shift in research focus to the study of protein sites of anesthetic action and especially to the effects of these drugs on ion channels (1, 2). Among the most studied molecular targets for these drugs are members of the Cysloop family of ligand-gated ion channels, including the glycine receptor (GlyR), 2 the primary inhibitory neurotransmitter receptor in the spinal cord and brain stem (3). Studies in rats have shown that GlyRs mediate the immobilizing effects of the anesthetics halothane, isoflurane, and cyclopropane (4). In transgenic mice expressing an alcohol-insensitive mutant GlyR, these receptors mediate, at least in part, the sedating and anesthetic effects of alcohol (5). These in vivo data agree with functional studies indicating that pharmacologically relevant concentrations of alcohols and volatile anesthetics potentiate GlyRs in both brain slices and heterologous expression systems (6 -9).Significant advances have been made in the understanding of the molecular mechanisms of alcohol and volatile anesthetic enhancement of GlyR function. The GlyR consists of a pentameric assembly of subunits surrounding a central, anion-conducting pore (10). Each of these subunits contains a large, N-terminal extracellular domain responsible for agonist binding, as well as four transmembrane (TM) domains, of which TM2 lines the channel pore and forms the channel gate (11). Mihic et al. (12) identified two amino acids, serine 267 (Ser-267) in TM2 and alanine 288 (Ala-288) in TM...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.