Biomedical subjects

William H Colledge

Publications and source records attributed to William H Colledge.

26 records · Page 2Linked to original sources

PubMed2003

Stella is a maternal effect gene required for normal early development in mice.

stella is a novel gene specifically expressed in primordial germ cells, oocytes, preimplantation embryos, and pluripotent cells. It encodes a protein with a SAP-like domain and a splicing factor motif-like structure, suggesting possible roles in chromosomal organization or RNA processing. Here, we have investigated the effects of a targeted mutation of stella in mice. We show that while matings between heterozygous animals resulted in the birth of apparently normal stella null offspring, stella-deficient females displayed severely reduced fertility due to a lack of maternally inherited Stella-protein in their oocytes. Indeed, we demonstrate that embryos without Stella are compromised in preimplantation development and rarely reach the blastocyst stage. stella is thus one of few known mammalian maternal effect genes, as the phenotypic effect on embryonic development is mainly a consequence of the maternal stella mutant genotype. Furthermore, we show that STELLA that is expressed in human oocytes is also expressed in human pluripotent cells and in germ cell tumors. Interestingly, human chromosome 12p, which harbours STELLA, is consistently overrepresented in these tumors. These findings suggest a similar role for STELLA during early human development as in mice and a potential involvement in germ cell tumors.

Amino Acid Sequence↗

PubMed2003

Intrinsic sympathomimetic activity of (-)-pindolol mediated through a (-)-propranolol-resistant site of the beta1-adrenoceptor in human atrium and recombinant receptors.

The beta-blocker (-)-pindolol produces intrinsic sympathomimetic activity manifested clinically by cardiostimulation, but the beta-adrenoceptor subtype, which mediates these effects, is unknown. Recent work indicates the existence of a (-)-propranolol-resistant site of the cardiac beta(1)-adrenoceptor and we propose that it mediates the cardiostimulation evoked by (-)-pindolol. We compared the interaction of (-)-pindolol both with human atrial myocardium and with recombinant beta(1)-adrenoceptors. The effects of (-)-pindolol on paced human atrial trabeculae were studied in the presence of 3-isobutyl-1-methylxanthine (IBMX; 20 microM). (-)-Pindolol caused small negative and positive inotropic effects at nanomolar and micromolar concentrations respectively, which were unaffected by N(G)-monomethyl-L-arginine (L-NMMA, 10 microM), inconsistent with an involvement of nitric oxide. (-)-Pindolol, in the presence of (-)-propranolol, increased atrial contractile force and cAMP through recombinant beta(1)-adrenoceptors with identical potency (-logEC(50)M=6.5). The positive inotropic effects of (-)-pindolol were resistant to blockade by L-748,337 (100 nM), a beta(3)-adrenoceptor antagonist. (-)-CGP12177, known to act through the (-)-propranolol-resistant site of the beta(1)-adrenoceptor, also increased with similar potency atrial contractile force (-logEC(50)M=7.6) and cAMP at recombinant beta(1)-adrenoceptors (-logEC(50)M=7.7). (-)-Pindolol blocked the effects of (-)-CGP12177 in human atrium and recombinant beta(1)-adrenoceptors with similar equilibrium dissociation constants (pK(B)=6.5 and 6.3). Thus, stimulant potency and blocking potency of (-)-pindolol against (-)-CGP12177 agree. In contrast, (-)-pindolol was 200-400 times more effective at blocking the effects of a catecholamine than the effects of (-)-CGP12177 in both human atrium (pK(B)=9.1) and at recombinant beta(1)-adrenoceptors (pK(B)=8.6). We conclude that the cardiostimulant effects of (-)-pindolol in human atrial myocardium are mediated through a (-)-propranolol-resistant site of the beta(1)-adrenoceptor with low affinity for (-)-pindolol. In contrast, (-)-pindolol blocks the effects of catecholamines through a high-affinity site of the beta(1)-adrenoceptor. beta(3)-Adrenoceptors are not involved in the atrial effects of (-)-pindolol.

1-Methyl-3-isobutylxanthine↗

PubMed2003

The GPR54 gene as a regulator of puberty.

BACKGROUND: Puberty, a complex biologic process involving sexual development, accelerated linear growth, and adrenal maturation, is initiated when gonadotropin-releasing hormone begins to be secreted by the hypothalamus. We conducted studies in humans and mice to identify the genetic factors that determine the onset of puberty. METHODS: We used complementary genetic approaches in humans and in mice. A consanguineous family with members who lacked pubertal development (idiopathic hypogonadotropic hypogonadism) was examined for mutations in a candidate gene, GPR54, which encodes a G protein-coupled receptor. Functional differences between wild-type and mutant GPR54 were examined in vitro. In parallel, a Gpr54-deficient mouse model was created and phenotyped. Responsiveness to exogenous gonadotropin-releasing hormone was assessed in both the humans and the mice. RESULTS: Affected patients in the index pedigree were homozygous for an L148S mutation in GPR54, and an unrelated proband with idiopathic hypogonadotropic hypogonadism was determined to have two separate mutations, R331X and X399R. The in vitro transfection of COS-7 cells with mutant constructs demonstrated a significantly decreased accumulation of inositol phosphate. The patient carrying the compound heterozygous mutations (R331X and X399R) had attenuated secretion of endogenous gonadotropin-releasing hormone and a left-shifted dose-response curve for gonadotropin-releasing hormone as compared with six patients who had idiopathic hypogonadotropic hypogonadism without GPR54 mutations. The Gpr54-deficient mice had isolated hypogonadotropic hypogonadism (small testes in male mice and a delay in vaginal opening and an absence of follicular maturation in female mice), but they showed responsiveness to both exogenous gonadotropins and gonadotropin-releasing hormone and had normal levels of gonadotropin-releasing hormone in the hypothalamus. CONCLUSIONS: Mutations in GPR54, a G protein-coupled receptor gene, cause autosomal recessive idiopathic hypogonadotropic hypogonadism in humans and mice, suggesting that this receptor is essential for normal gonadotropin-releasing hormone physiology and for puberty.

Animals↗

PubMed2003

In vivo gene expression: DNA electrotransfer.

The use of electric pulses to deliver therapeutic molecules to tissues and organs in vivo is a rapidly growing field of research. Electrotransfer can be used to deliver a wide range of potentially therapeutic agents, including drugs, proteins, oligonucleotides, RNA and DNA. Optimization of this approach depends upon a number of parameters such as target organ accessibility, cell turnover, microelectrode design, electric pulsing protocols and the physiological response to the therapeutic agent. Many organs have been successfully transfected by electroporation, including skin, liver, skeletal and cardiac muscle, male and female germ cells, artery, gut, kidney, retinal ganglion cells, cornea, spinal cord, joint synovium and brain. Electrotransfer technology is relevant in a variety of research and clinical settings including cancer therapy, modulation of pathogenic immune reactions, delivery of therapeutic proteins and drugs, and the identification of drug targets by the modulation of normal gene expression. This, together with the capacity to deliver very large DNA constructs, greatly expands the research and clinical applications of in vivo DNA electrotransfer.

Animals↗

PubMed2002

Aminoglycoside suppression of a premature stop mutation in a Cftr-/- mouse carrying a human CFTR-G542X transgene.

Cystic fibrosis (CF) is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein. Since approximately 5% of all mutant CF alleles are stop mutations, it can be calculated that approximately 10% of CF patients carry a premature stop mutation in at least one copy of the CFTR gene. Certain ethnic groups, such as the Ashkenazi Jewish population, carry a much higher percentage of CF stop mutations. Consequently, a therapeutic strategy aimed at suppressing this class of mutation would be highly desirable for the treatment of this common genetic disease. We have shown previously that aminoglycoside antibiotics can suppress premature stop mutations in the CFTR gene in a bronchial epithelial cell line [Nat Med (1997) 3:1280]. To address whether aminoglycosides can suppress a CFTR premature stop mutation in an animal model, we constructed a transgenic mouse with a null mutation in the endogenous CFTR locus (Cftr-/-) that also expressed a human CFTR-G542X cDNA under control of the intestinal fatty acid binding protein promoter. We then investigated whether the daily administration of the aminoglycoside antibiotics gentamicin or tobramycin could restore the expression of a detectable level of CFTR protein. Immunofluorescence staining of intestinal tissues from Cftr-/- hCFTR-G542X mice revealed that gentamicin treatment resulted in the appearance of hCFTR protein at the apical surface of the glands of treated mice. Weaker staining was also observed in the intestinal glands following tobramycin treatment. Short-circuit current measurements made on intestinal tissues from these mice demonstrated that a significant number of positive cAMP-stimulated transepithelial chloride current measurements could be observed following gentamicin treatment (P=0.008) and a near significant number following tobramycin treatment (P=0.052). When taken together, these results indicate that gentamicin, and to a lesser extent tobramycin, can restore the synthesis of functional hCFTR protein by suppressing the hCFTR-G542X premature stop mutation in vivo.

Action Potentials↗

PubMed2002

Murine model of autosomal dominant retinitis pigmentosa generated by targeted deletion at codon 307 of the rds-peripherin gene.

We introduced a targeted single base deletion at codon 307 of the rds-peripherin gene in mice, similar mutations being known to cause autosomal dominant retinitis pigmentosa (RP) in man. Histopathological and electroretinographic analysis indicate that the retinopathy in mice homozygous for the codon 307 mutation appears more rapid than that in the naturally occurring null mutant, the rds(-/-) mouse, suggesting that the rds-307 mutation displays a dominant negative phenotype in combination with that due to haplosufficiency. RP is the most prevalent cause of registered visual handicap in those of working age in developed countries, the 50 or so mutations so far identified within the RDS-peripherin gene accounting for up to 10% of dominant cases of the disease. Given the sequence homologies that exist between the murine rds-peripherin and the human RDS-peripherin gene, this disease model, the first to be generated for peripherin-based RP using gene targeting techniques, should in principle be of value in the work-up in mice of therapeutics capable of targeting transcripts derived from the human gene.

Amino Acid Sequence↗

PubMed2002

Slowed conduction and ventricular tachycardia after targeted disruption of the cardiac sodium channel gene Scn5a.

Voltage-gated sodium channels drive the initial depolarization phase of the cardiac action potential and therefore critically determine conduction of excitation through the heart. In patients, deletions or loss-of-function mutations of the cardiac sodium channel gene, SCN5A, have been associated with a wide range of arrhythmias including bradycardia (heart rate slowing), atrioventricular conduction delay, and ventricular fibrillation. The pathophysiological basis of these clinical conditions is unresolved. Here we show that disruption of the mouse cardiac sodium channel gene, Scn5a, causes intrauterine lethality in homozygotes with severe defects in ventricular morphogenesis whereas heterozygotes show normal survival. Whole-cell patch clamp analyses of isolated ventricular myocytes from adult Scn5a(+/-) mice demonstrate a approximately 50% reduction in sodium conductance. Scn5a(+/-) hearts have several defects including impaired atrioventricular conduction, delayed intramyocardial conduction, increased ventricular refractoriness, and ventricular tachycardia with characteristics of reentrant excitation. These findings reconcile reduced activity of the cardiac sodium channel leading to slowed conduction with several apparently diverse clinical phenotypes, providing a model for the detailed analysis of the pathophysiology of arrhythmias.

Animals↗

PubMed2002

DeltaF508-CFTR causes constitutive NF-kappaB activation through an ER-overload response in cystic fibrosis lungs.

The clinical course of Cystic Fibrosis is characterized by recurrent pulmonary infections which ultimately lead to death by respiratory failure. The most common CF causing mutation, deltaF508-CFTR, produces an incorrectly folded protein, which accumulates within the endoplasmic reticulum. However, the molecular mechanism by which the deltaF508-CFTR protein facilitates pulmonary infection and inflammation remains unclear. Here we show that the expression of deltaF508-CFTR causes a constitutive activation of the pro-inflammatory transcription factor NF-kappaB by eliciting an ER stress reaction, the ER-overload response. This endogenous NF-kappaB activation stimulates the transcription of pro-inflammatory cytokines thereby commencing an inflammatory cascade within the CF lung.

Animals↗