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Biomedical subjects

A Ryan

Publications and source records attributed to A Ryan.

At least 19 recordsLinked to original sources
PubMed1995

Transgenic knockouts reveal a critical requirement for pancreatic beta cell glucokinase in maintaining glucose homeostasis.

The secretion of insulin is controlled by the rate of glucose metabolism in the pancreatic beta cells. As phosphorylation by glucokinase (GLK) appears to be the rate-limiting step for glucose catabolism in beta cells, this enzyme may be the glucose sensor. To test this possibility and to resolve the relative roles of liver and beta cell GLK in maintaining glucose levels, we have generated mice completely deficient in GLK and transgenic mice in which GLK is expressed only in beta cells. In mice with only one GLK allele, blood glucose levels are elevated and insulin secretion is reduced. GLK-deficient mice die perinatally with severe hyperglycemia. Expression of GLK in beta cells in the absence of expression in the liver is sufficient for survival. These mice demonstrate the critical need for beta cell GLK in maintaining normal glucose levels and provide a novel model for one form of noninsulin-dependent diabetes.

Alleles↗
PubMed1995

Ligand-independent repression by the thyroid hormone receptor mediated by a nuclear receptor co-repressor.

Thyroid-hormone and retinoic-acid receptors exert their regulatory functions by acting as both activators and repressors of gene expression. A nuclear receptor co-repressor (N-CoR) of relative molecular mass 270K has been identified which mediates ligand-independent inhibition of gene transcription by these receptors, suggesting that the molecular mechanisms of repression by thyroid-hormone and retinoic-acid receptors are analogous to the co-repressor-dependent transcriptional inhibitory mechanisms of yeast and Drosophila.

Amino Acid Sequence↗
PubMed1995

Inactivation of the mouse Huntington's disease gene homolog Hdh.

Huntington's disease (HD) is a dominant neurodegenerative disorder caused by expansion of a CAG repeat in the gene encoding huntingtin, a protein of unknown function. To distinguish between "loss of function" and "gain of function" models of HD, the murine HD homolog Hdh was inactivated by gene targeting. Mice heterozygous for Hdh inactivation were phenotypically normal, whereas homozygosity resulted in embryonic death. Homozygotes displayed abnormal gastrulation at embryonic day 7.5 and were resorbing by day 8.5. Thus, huntingtin is critical early in embryonic development, before the emergence of the nervous system. That Hdh inactivation does not mimic adult HD neuropathology suggests that the human disease involves a gain of function.

Animals↗
PubMed1995

The changing epidemiology of invasive meningococcal disease in Canada, 1985 through 1992. Emergence of a virulent clone of Neisseria meningitidis.

OBJECTIVE: To describe the occurrence of invasive meningococcal disease (IMD) in Canada with respect to demographic variables and characteristics of the isolated strains of Neisseria meningitidis. DESIGN: National surveillance case series. SETTING: Canada, 1985 through 1992. OUTCOME MEASURES: Morbidity and mortality. MAIN RESULTS: The incidence of IMD averaged 1.38 per 100,000 person-years, with considerable regional variation. In 1988, serogroup C organisms became more common, with one strain of the electrophoretic type 37 (ET-37) complex of N meningitidis, termed ET-15, the predominant group C strain identified. With the increase in group C disease, a greater proportion of cases were older than 5 years. By 1991, ET-15 was the most common strain identified in most parts of the country. Electrophoretic type 15 had a case fatality of 17.8% vs 8.1% for all other IMD (P < .001). Among cases 20 years and older the case fatality for ET-15 was 22.4%. CONCLUSIONS: The group C, ET-15 strain of N meningitidis, first identified in Canada, was more virulent than other prevalent strains during this period. Active surveillance, rapid identification, and typing of N meningitidis will assist public health decision making in the control of emerging strains.

Adolescent↗
PubMed1995

Meningococcal infections in the Province of Québec, Canada, during the period 1991 to 1992.

A total of 234 strains of Neisseria meningitidis obtained from hospitalized patients living in the province of Québec during the period 1991 to 1992 were characterized according to their serogroup, serotype, subtype, electrophoretic type, and antimicrobial susceptibility. All these strains were recovered from sterile body fluids, except for one strain that was isolated postmortem from a cutaneous lesion. For both years, serogroup C was the most prevalent (69.7%), followed by serogroup B (27.4%). Serotype 2a represented 80.3% of serogroup C isolates, and P1.2 was the most common subtype associated with this serotype. Clone ET 15 accounted for 76.5% of serogroup C isolates and 90.0% of serotype 2a strains. Although meningococcal disease occurred mostly in children under the age of 5 (9.7 cases per 100,000 children), with a peak incidence for children under 1 (20.3 cases per 100,000 children), most fatalities occurred among teenagers (12 to 19 years old). The total fatality rate was 11.5%, and serogroup C strains were responsible for 88.9% of these fatalities. Thirteen strains had a reduced susceptibility to penicillin G, and 28 strains were resistant to sulfadiazine. One strain was resistant to both rifampin and sulfadiazine and showed a reduced susceptibility to penicillin G.

Adolescent↗
PubMed1995

Epidermal growth factor and basic fibroblast growth factor are induced in guinea-pig tympanic membrane following traumatic perforation.

Epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF or FGF-2) have been shown to enhance the healing of traumatic tympanic membrane (TM) perforations. The action of EGF and bFGF in the TM repair process remains unknown. This study was designed to determine the expression of EGF and bFGF in normal and injured TM by immunohistochemistry. EGF was detected in normal TM mainly in the annulus tympani area. After a perforation in the TM posterior/superior quadrant, EGF was detected around the perforated area in polynuclear cells, in pericytes and in basal epithelial cells. EGF was also detected in the antero/superior quadrant in basal epithelial cells and pericytes. The peak of EGF detection was observed 3 days after the perforation. bFGF was not detected in normal TM, but it was expressed 3 days after a traumatic perforation mainly in the perforated area in pericytes and in polynuclear cells. This study suggests that EGF and bFGF are involved in the control of TM acute perforation repair. These findings help to explain the accelerated healing of TM perforations that are seen after application of FGF or EGF, and suggest that antibodies against these growth factors would retard the healing process.

Animals↗
PubMed1994

Expression of mRNAs encoding alpha and beta subunit isoforms of Na,K-ATPase in the vestibular labyrinth and endolymphatic sac of the rat.

The distribution of mRNAs coding for three different isoforms of the alpha and two of the beta subunit of Na,K-ATPase was studied in the rat vestibular system using in situ mRNA hybridization. The dark cells of the utricular macula and of the ampullae of the semicircular canals expressed high levels of mRNA encoding the alpha 1 and beta 2 isoforms of the Na,K-ATPase, a composition that in the cochlea has been uniquely found in the stria vascularis. However, in the dark cells it was coupled with a weak expression of beta 1. The sensory epithelia of the vestibular system showed alpha 1 and beta 1 expression at much higher levels than in the cochlear sensory epithelium. Weak expression limited to the alpha 1, beta 1, and beta 2 isoforms was observed in the endolymphatic sac, contrasting previous cytochemical results which suggested extensive Na,K-ATPase activity to the sac. The results support the widely held hypothesis that the vestibular dark cells play a role similar to that of the stria vascularis in endolymph production. They indicate that the ion transport requirements of the vestibular sensory epithelia may be different than those in the cochlea. They also suggest that the endolymphatic sac may not be a major site of inner ear ion exchange.

Animals↗
PubMed1993

Chicken sterol carrier protein 2/sterol carrier protein x: cDNA cloning reveals evolutionary conservation of structure and regulated expression.

The chicken is a useful model for studies of lipid biochemistry because of the profound changes in lipid metabolism during development and the marked effects of estrogen on its lipids. Here we report the cloning of a cDNA encoding chicken sterol carrier protein 2 (SCP2)/sterol carrier protein x (SCPx), proteins that are believed to play key roles in intracellular lipid movement and metabolism. The 2.4-kb clone, isolated from a liver cDNA library by homology screening with a rat SCP2 cDNA, encodes a 58-kDa polypeptide, SCPx, which encompasses the sequence for SCP2 at its C-terminus. Comparison of the deduced amino acid sequence of the chicken protein with those of mammals revealed conservation of structure from an evolutionary standpoint. Like the other vertebrate SCPx proteins, the chicken protein contains a conserved Arg-Gly-Asp sequence and a cysteine residue in the N-terminus that aligns with the active site cysteine of Escherichia coli 3-ketoacyl-CoA thiolase, a protein that was previously shown to be homologous to vertebrate SCPx. Northern blot analysis of poly(A)+ RNA from different chicken tissues revealed two mRNA species, one of 2.5 kb, encoding SCPx, and one of 1.4 kb, presumably encoding SCP2. High levels of the 2.5 and 1.4-kb mRNAs were found in liver, intestine, and ovarian granulosa cells, consistent with a role for these proteins in lipid metabolism. There was no change in the 2.5-kb mRNA in chicken liver with development (Day 20 embryo to 4 weeks posthatch), but there was a 10-fold increase in the 1.4-kb mRNA by 1 week posthatch. Treatment of roosters with a single injection of estradiol (25 mg/kg) caused a twofold increase in the 2.5-kb mRNA in liver at 6 h after estradiol administration, reaching a maximum fourfold increase at 48 h, while the 1.4-kb mRNA increased twofold at 48 h. The two SCP2/SCPx mRNAs were most abundant in granulosa cells from small follicles. A reduction in SCP2/SCPx gene expression was observed with follicular maturation, correlating with falling estrogen production. In summary, we have documented (i) marked conservation of SCP2/SCPx structure across species and (ii) developmental and hormonal regulation of the mRNAs which encode proteins thought to be involved in lipid metabolism.

Amino Acid Sequence↗
PubMed1993

Histological study of the healing of traumatic tympanic membrane perforation after basic fibroblast growth factor application.

Basic fibroblast growth factor (bFGF) can stimulate the proliferation and differentiation of keratinocytes, fibroblasts, and endothelial cells. These cells are involved during the healing of tympanic membrane (TM) perforations. Light and electron microscopy examinations were used to study the histology of TM healing after application of 400 ng of bFGF on the perforation. The progress of healing is accelerated, but the basic healing process is unchanged, i.e., epithelial proliferation first closes the perforation and is then followed by connective tissue growth. There is more connective tissue in the TM receiving bFGF, and extracellular fibers are better oriented. No significant increase of neoangiogenesis was detected in the treated TM. In the nonperforated area of treated TM, an extensive hyperplasia of the submucosal connective tissue is observed. These results demonstrate that bFGF can produce a TM scar containing more connective tissue, which may be of benefit in the prevention of atrophic healed TM.

Animals↗
PubMed1993

Direct application of basic fibroblast growth factor improves tympanic membrane perforation healing.

Topical application of basic fibroblast growth factor (b-FGF) on tympanic membrane (TM) perforations was studied in guinea pigs. One-millimeter simple round TM perforations or 2-mm TM perforations with medially flapped borders were performed. Either b-FGF or placebo was instilled in each ear on the day of surgery and daily thereafter. Treatment was applied either directly to the perforation or to a Gelfoam pledget over the defect. When no scaffolding material was interposed, b-FGF induced a faster healing response characterized by a hyperplastic but linear subepidermal connective tissue reaction compared to the control. When Gelfoam was interposed as a scaffold, a voluminous scar protruding into the middle ear cavity and involving the ossicles was observed in both b-FGF and control animals. Gelfoam-induced scars did not decrease after long-term observation, therefore discouraging its use.

Animals↗
PubMed1992

Radiomimetic cell cycle delay induced by tetranodecanoyl phorbol acetate is enhanced by caffeine and by the protein kinase inhibitor 2-aminopurine.

The tumour promoter and protein kinase C agonist, 12-O-tetranodecanoyl-phorbol-13-acetate (TPA), has been reported to show a radiomimetic action because it transiently delays the passage of HeLa cells through the G2 phase, as do ionizing radiation and other DNA damaging agents. Caffeine is known to override the G2 delay imposed by DNA damage; it is shown here that caffeine does not override the radiomimetic delay imposed by TPA in HeLa, but instead enhances it, without affecting G2 progression in control cells. Most of the other agents which more specifically affect some of the diverse range of caffeine targets either do not affect G2 progression after TPA, or delay G2 progression in control cells and exert a further delay in the presence of TPA. The exception is 2-aminopurine, a protein kinase inhibitor which has been shown to have an action similar to that of caffeine is allowing progression of the cell cycle to mitosis after the inhibition of DNA synthesis, without affecting normal cycle progression through G2. This agent, like caffeine, also has the contrary action of retarding cycle progression after TPA. It is concluded that the G2 delays induced by ionizing radiation and by TPA operate by different mechanisms, which are modulated in opposite senses by mechanisms involving protein kinase inhibition.

2-Aminopurine↗
PubMed1991

Identification of a cell-surface antigen associated with activated T lymphoblasts and activated platelets.

We have identified and biochemically characterized an antigen, 8A3, which is expressed on activated T lymphoblasts and activated platelets. Monoclonal antibodies to 8A3 were raised against the primitive lymphoid/myeloid cell line KG1a and additionally bound to the erythroleukemia-derived cell line HEL, whilst exhibiting little or no reactivity with a panel of other hematopoietic cell lines. The 8A3 antigen was expressed on poorly differentiated T-cell leukemias and on phytohemagglutinin-activated T-cells maintained in interleukin-2 (7,000 sites/cell). This antigen, though not detected on resting platelets, was expressed on thrombin-activated platelets (2,000 sites/platelet). Antibodies to 8A3 identified polypeptides of Mr 170,000 and 150,000 in lysates of surface-iodinated KG1a cells, T lymphoblasts, and activated platelets under both reducing and nonreducing conditions. However, peptide mapping and susceptibily to glycosidases indicated that the 8A3 antigen was a monomeric glycoprotein of Mr 170,000 which contained two N-linked endoglycosidase H-sensitive glycans, and that the Mr 150,000 structure was derived from it by proteolytic degradation. The 8A3 antigen was not detectably phosphorylated in KG1a cells in vivo, nor did immune complexes containing it exhibit kinase activity in vitro. Structural and serologic characteristics of the 8A3 antigen indicate that it is different from other previously described leukocyte activation antigens including transferrin receptors, interleukin-2 receptors, members of the integrin family of adhesion molecules, or "restricted" members of the leukocyte-common antigen/CD45 cluster. Furthermore, the 8A3 antigen does not appear to be related to the other previously described activation-specific platelet molecule, GMP140/PADGEM. This antibody may be useful in monitoring T-cell activation status in some clinical situations and in characterizing clinically relevant activation-associated platelet membrane alterations.

Animals↗
PubMed1991

The response to human rIL-1, rIL-2, and rTNF in the middle ear of guinea pigs.

Human recombinant interleukin 1 (rIL-1), interleukin 2 (rIL-2), or tumor necrosis factor (rTNF) were injected transtympanically into the middle ear of normal guinea pigs. Effusion volume and cellular content were determined after sacrifice and rapid dissection of the ear. By 24 hours, rIL-2 (100 U) had produced a cellular effusion (77% to 92% polymorphonuclear neutrophil leukocytes), which cleared by 72 hours. rTNF (10 U) yielded a cellular effusion (12% to 67% lymphocytes) at 24 hours, which cleared by 48 hours. rIL-1 (100 U) did not produce significant effusion when compared to control. rIL-2 and rTNF cause an inflammatory effusion in the middle ear. To the extent they are generated in the middle ear during otitis media, these cytokines have the potential to contribute to the pathogenesis of otitis media with effusion.

Animals↗
PubMed1991

Improved healing of tympanic membrane perforations with basic fibroblast growth factor.

We have investigated the effects of basic fibroblast growth factor (FGF) on the healing of tympanic membrane (TM) perforations. In the first series of experiments, a simple, round 1-mm perforation was made in the membrane and the effects of basic FGF examined. In a second series of experiments, basic FGF was tested on 2-mm perforations in which the borders were folded inward in order to delay normal healing. Topical applications of saline or basic FGF were administered onto gelfoam overlays of the TM perforations in 51 guinea pigs by delivering 5 microliters aliquots of PBS or 5 microliters of PBS containing 1 microgram of basic FGF on the day of surgery and daily thereafter. Repair of the lesions was evaluated 3, 5 or 8 days after surgery. The results show that basic FGF mediates faster healing of TM perforations by inducing rapid proliferation of the subepithelial connective tissue layer.

Animals↗
PubMed1991

Wocko, a neurological mutant generated in a transgenic mouse pedigree.

Naturally occurring mutations involving the nervous system have provided virtually all of our current understanding of the genetic regulation of neural development (Caviness and Rakic, 1978). The difficulty of isolating the corresponding genes, however, has precluded a molecular analysis of these mutants. Insertional mutagenesis, induced by microinjection of DNA into fertilized ova to produce transgenic animals, provides a molecular tag that marks the site of the mutational event. In this article, we describe a transgenic neurological mutation, designated wocko (Wo), which disrupts the development of the inner ear. These mutant mice display a dominant behavioral phenotype that consists of circling, hyperactivity, and head tossing, reminiscent of the shaker/waltzer class of mutants, and they display a recessive homozygous sublethal phenotype. Anatomical analyses showed that both structural and neural components of the vestibular system were disrupted, while analyses of mutant fetuses showed that these morphological abnormalities were due to aberrant development. Although low levels of transgene expression were detected using a sensitive PCR assay, several nonmutant pedigrees that contain the same construct also expressed the transgene in the inner ear, suggesting that low levels of transgene expression alone were not responsible for the wocko phenotype. Because the integrated transgene provides a marker to clone the wocko mutation, the analysis of this mutant will give unique insight into the molecular genetics of inner ear development and into a broad class of neurological mutations that affect the inner ear.

Animals↗