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Biomedical subjects

A A Toye

Publications and source records attributed to A A Toye.

9 recordsLinked to original sources
PubMed2005

A genetic and physiological study of impaired glucose homeostasis control in C57BL/6J mice.

AIMS/HYPOTHESIS: C57BL/6J mice exhibit impaired glucose tolerance. The aims of this study were to map the genetic loci underlying this phenotype, to further characterise the physiological defects and to identify candidate genes. METHODS: Glucose tolerance was measured in an intraperitoneal glucose tolerance test and genetic determinants mapped in an F2 intercross. Insulin sensitivity was measured by injecting insulin and following glucose disposal from the plasma. To measure beta cell function, insulin secretion and electrophysiological studies were carried out on isolated islets. Candidate genes were investigated by sequencing and quantitative RNA analysis. RESULTS: C57BL/6J mice showed normal insulin sensitivity and impaired insulin secretion. In beta cells, glucose did not stimulate a rise in intracellular calcium and its ability to close KATP channels was impaired. We identified three genetic loci responsible for the impaired glucose tolerance. Nicotinamide nucleotide transhydrogenase (Nnt) lies within one locus and is a nuclear-encoded mitochondrial proton pump. Expression of Nnt is more than sevenfold and fivefold lower respectively in C57BL/6J liver and islets. There is a missense mutation in exon 1 and a multi-exon deletion in the C57BL/6J gene. Glucokinase lies within the Gluchos2 locus and shows reduced enzyme activity in liver. CONCLUSIONS/INTERPRETATION: The C57BL/6J mouse strain exhibits plasma glucose intolerance reminiscent of human type 2 diabetes. Our data suggest a defect in beta cell glucose metabolism that results in reduced electrical activity and insulin secretion. We have identified three loci that are responsible for the inherited impaired plasma glucose tolerance and identified a novel candidate gene for contribution to glucose intolerance through reduced beta cell activity.

Animals↗
PubMed1999

Novel endogenous retroviral sequences in the chicken genome closely related to HPRS-103 (subgroup J) avian leukosis virus.

HPRS-103, the prototype of avian leukosis virus (ALV) subgroup J, is a recently identified retrovirus associated with myeloid leukosis in meat-type chickens. Although this virus shows high sequence identity to other ALV subgroups within the gag and pol genes, its env gene is highly diverged (with only about 40% sequence identity) from other ALV subgroups. On the other hand, the sequence of the env gene of HPRS-103 was 75% identical to that of E51, a member of the EAV family of endogenous avian retroviruses. It is reported here that the chicken genome also contains another EAV-related element, EAV-HP, showing much greater sequence identity (over 97%) to the HPRS-103 env gene. Southern blotting analysis showed that EAV-HP-related sequences were distinct from EAV-O and were present in all lines of chicken examined and in grey jungle fowl, but were absent from several other avian species. The potential role of these endogenous sequences in the evolution of ALV subgroup J viruses is discussed.

Amino Acid Sequence↗
PubMed1998

Mapping the genome of Eimeria tenella: use of a yeast artificial chromosome library as the basis for a physical map.

Efforts to derive a physical map of the genome of Eimeria tenella are being made to complement genetic mapping and to assist in the production of an integrated map. A large insert library of DNA from the Houghton (H) reference strain of E. tenella has been constructed in yeast artificial chromosomes (YACs). The library contains a tenfold E. tenella genome equivalent consisting of 3177 clones arrayed in 96-well microtitre plates and gridded on nylon membranes at 1728 clones/86 cm2. Size fractionation of a random sample of 185 YACs revealed an average insert size of approximately 170 kb. Hybridisation of four E. tenella single-copy probes to the gridded colony filters produced around four or more positive clones. A probe representing the whole of the 1.2-Mb chromosome 2, excised from a preparative gel following pulsed-field gel electrophoresis, revealed between 80 and 100 positive clones.

Animals↗
PubMed1998

Targeting of marker loci to chicken chromosome 16 by representational difference analysis.

Representational difference analysis (RDA) was initially used to identify differences between two inbred lines of chickens, line N and line 15I, on which the Compton mapping reference population is based. RDA was subsequently used to identify marker loci targeted specifically to chicken chromosome 16. Chromosome 16 contains the major histocompatibility complex (MHC), nucleolar organiser region (NOR) and Rfp-Y complex. To generate markers specific for this chromosome a bird was selected from the Compton mapping reference population which had inherited N line alleles for the MHC, NOR and Rfp-Y regions on this chromosome. DNA from this bird was compared with pooled DNA from 16 of its siblings, all of which had inherited line 15I alleles for the MHC, NOR and Rfp-Y regions. Initially amplicons were derived from BamHI digested samples, RDA products were cloned after the first round of hybridisation and 113 clones were investigated: 45 of these identified BamHI polymorphisms in this population. Of the 45 polymorphic clones, 17 have been mapped in the reference population so far, and these have identified seven new loci on chromosome 16. Interestingly a group of 16 other loci were linked on chromosome 4. The same birds were also compared by RDA following digestion with TaqI. Again large numbers of clones were generated of which 65 were investigated. Of these 17 clones were polymorphic and of five clones mapped so far three lie on chromosome 16. Two of the loci mapped to chromosome 16 have been used to identify yeast artificial chromosome (YAC) clones.

Animals↗
PubMed1997

A yeast artificial chromosome (YAC) library containing 10 haploid chicken genome equivalents.

We report the construction of a YAC library that provides 10-fold redundant coverage of the chicken genome. The library was made by transforming S. cerevisiae AB1380 with YAC constructs consisting of partially digested and size fractionated (>465 kb) EcoRI genomic fragments ligated to pCGS966 YAC vector arms. The primary library provides 8.5-fold redundant coverage and consists of 16,000 clones arrayed in duplicate 96-well microtiter plates and gridded on nylon membranes at high density (18,000 clones/484cm2). The average insert size, 634 kb, was derived from size fractionation of a random sample of 218 YACs. Hybridization of five unlinked chicken genes to colony blots revealed six or more positive clones. This is consistent with the theoretical expectation from average insert sizes and number of clones. A second collection of clones consists of a further 20,000 colonies, of which 20% contain inserts larger than 450 kb and 80% contain only coligated vector arms. We estimate that these clones provide a further 1.5-fold redundant coverage of the chicken genome; thus, the total collection of 36,000 clones provides 10-fold redundant coverage of the chicken genome. The library is intended as a resource for fine-scale analysis of the organization of the chicken genome and is presently being used to construct a contig map of chicken Chromosome (Chr) 16, which contains the MHC and nucleolar organizer.

Animals↗