The human glucagon receptor encoding gene: structure, cDNA sequence and chromosomal localization

Characterization of the human glucagon-receptor-encoding gene (GGR) should provide a greater understanding of blood glucose regulation and may reveal a genetic basis for the pathogenesis of diabetes. A cDNA encoding a complete functional human glucagon receptor (GGR) was isolated from a liver cDNA library by a combination of polymerase chain reaction and colony hybridization. The cDNA encodes a receptor protein with 80% identity to rat GGR that binds [¹²⁵I] glucagon and transduces a signal leading to increases in the concentration of intracellular cyclic adenosine 3′,5′-monophosphate. Southern blot analysis of human DNA reveals a hybridization pattern consistent with a single GGR locus. In situ hybridization to metaphase chromosome preparations maps the GGR locus to chromosome 17q25. Analysis of the genomic sequence shows that the coding region spans over 5.5 kb and is interrupted by 12 introns.     

A model of the role of adaptation and disadaptation in olfactory receptor neurons: implications for the coding of temporal and intensity patterns in odor signals

Natural odors occur as turbulent plumes resulting in spatiallyand temporally variable odor signals at the chemoreceptor cells.Concentrations can fluctuate widely within discrete packetsof odor and individual packets are very intermittent and unpredictable.Chemoreceptor cells display the temporally dynamic propertiesof adaptation and disadaptation, which serve to alter theirresponses to these fluctuating odor patterns. A computationalmodel, modified from one previously published, was used to investigate,the effect of adaptation and recovery of adaptation (disadaptation)on the spike output of model olfectory receptor cells undernatural stimulus conditions. The response characteristics ofmodel cells were based upon empirically determined dose-response,adaptation, disadaptation and flicker fusion properties of peripheralolfactory cells. The physiological properties of the model cell(adaptation and disadaptation rate and the dose-response relationship)could be modified independently, allowing assessment of therole of each in shaping the responses of the model cell. Completeadaptation and disadaptation time courses ranged from 500 ms(rapid cells) to 10 s (slow cells). The stimuli for the modelcells were quantified odor plume recordings obtained under avariety of biologically relevant flow conditions. As expected,the rapidly adapting model cells displayed different responsecharacteristics than the slowly adapting model cells to identicaltemporal odor profiles. Responses of the model cells dependedupon their adaptation and disadaptation rates, and the frequencycharacteristics of the odor presentation. These results indicatethat adaptation and disadaptation determine the range of concentrationfluctuations over which a particular cell will respond. Thus,these properties function as an olfactory equivalent of a band-passfilter in electronics. This type of filtering has implicationsfor the extraction of information from odor signals, men isthe coding of temporal and intensity features.     

Localization of a New Type of X-Linked Liver Glycogenosis to the Chromosomal Region Xp22 Containing the Liver α-Subunit of Phosphorylase Kinase (PHKA2)

We describe here a new type of X-linked liver glycogen storage disease. The main symptoms include liver enlargement and growth retardation. The clinical and biochemical abnormalities of this glycogenosis are similar to those of classical X-linked liver glycogenosis due to phosphorylase kinase deficiency (XLG). However, in contrast to patients with XLG, the patients described here have no reduced phosphorylase kinase activity in erythrocytes and leukocytes, and no enzyme deficiency could be found. Linkage analysis of four families with this X-linked type of liver glycogenosis assigned the disease gene to Xp22. Lod scores obtained with the markers DXS987, DXS207, and DXS999 were 3.97, 2.71, and 2.40, respectively, all at 0% recombination. Multipoint linkage analysis localized the disease gene between DXS143 and DXS989 with a maximum lod score of 4.70 at θ = 0, relative to DXS987. As both the classical XLG gene and the liver α-subunit of PHK (PHKA2) are also located in Xp22, this variant type of XLG may be allelic to classical XLG, and both diseases may be caused by mutations in PHKA2. Therefore, we propose to classify XLG as XLG type I (the classical type of XLG) and XLG type II (the variant type of XLG).     

The Location of a Disease-Associated Polymorphism and Genomic Structure of the Human 52-kDa Ro/SSA Locus (SSA1)

Sera from approximately 30% of patients with systemic lupus erythematosus (SLE) contain high titers of autoantibodies that bind to the 52-kDa Ro/SSA protein. We previously detected polymorphisms in the 52-kDa Ro/SSA gene (SSA1) with restriction enzymes, one of which is strongly associated with the presence of SLE (P < 0.0005) in African Americans. A higher disease frequency and more severe forms of the disease are commonly noted among these female patients. To determine the location and nature of this polymorphism, we obtained two clones that span 8.5 kb of the 52-kDa Ro/SSA locus including its upstream regulatory region. Six exons were identified, and their nucleotide sequences plus adjacent noncoding regions were determined. No differences were found between these exons and the coding region of one of the reported cDNAs. The disease-associated polymorphic site suggested by a restriction enzyme map and confirmed by DNA amplification and nucleotide sequencing was present upstream of exon 1. This polymorphism may be a genetic marker for a disease-related variation in the coding region for the protein or in the upstream regulatory region of this gene. Although this RFLP is present in Japanese, it is not associated with lupus in this race.     

Molecular genetic studies of Creutzfeldt-Jakob disease

Genetic study of over 200 cases of Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker disease (GSS), fatal familial insomnia (FFI), and kuru have brought a reliable body of evidence that the familial forms of CJD and all known cases of GSS and FFI are linked to germline mutations in the coding region of the PRNP gene on chromosome 20, either point substitutions or expansion of the number of repeat units. No pathogenic mutations have so far been found in sporadic or infectious forms of CJD, although there are features of genetic predisposition in iatrogenic CJD and kuru. In FFI and familial CJD, clinically and pathologically distinct syndromes that are both linked to the 178^Asp→Asn substitution, phenotypic expression is dependent on a polymorphism at codon 129. Synthetic peptides homologous to several regions of PrP spontaneously form insoluble amyloid fibrils with unique morphological characteristics and polymerization tendencies. Peptides homologous to mutated regions of PrP exhibit enhanced fibrilogenic properties and, if mixed with the wild-type peptide, produce even more abundant and larger fibrous aggregates. A similar process in vivo may lead to amyloid accumulation and disease, and transmission of “baby fibrils” may induce disease in other hosts.     

Algae as indicators of environmental change

Despite an increased awareness by governments and the general public of the need for protecting all types of aquatic habitats, human impacts continue to impair the services that these ecosystems provide. Increased monitoring activities that locus on all major biological compartments are needed to quantify the present condition of Earth's aquatic resources and to evaluate the effectiveness of regulations designed to rehabilitate damaged ecosystems. Algae are an ecologically important group in most aquatic ecosystems but are often ignored as indicators of aquatic ecosystem change. We attribute this situation both to an underappreciation of the utility of algal indicators among non-phycologists and to a lack of standardized methods for monitoring with algae.Because of their nutritional needs and their position at the base of aquatic foodwebs, algal indicators provide relatively unique information concerning ecosystem condition compared with commonly used animal indicators. Algae respond rapidly and predictably to a wide range of pollutants and, thus, provide potentially useful early warning signals of deteriorating conditions and the possible causes. Algal assemblages provide one of the few benchmarks for establishing historical water quality conditions and for characterizing the minimally impacted biological condition of many disturbed ecosystems. Preliminary comparisons suggest that algal indicators are a cost-effective monitoring tool as well.Based on available evidence from field studies, we recommend development of taxonomic indicators based on diatoms (Bacillariophyceae) as a standardized protocol for monitoring ecosystem change. Both population- and community-level indices have inherent strengths, and limitations and information from both levels of biological organization should be utilized in tandem. However, further information concerning species tolerances to a variety of anthropogenic stressors is needed if autecological indices are to be used routinely for monitoring purposes. While functional measures (e.g. productivity) may also prove useful as monitoring tools, further investigation is required to characterize the reliability of alternative methodologies and to assess the consistency of these indicators under varying field conditions.Author for correspondence     

Suppression of phaseolin and lectin in seeds of common bean, Phaseolus vulgaris L.: increased accumulation of 54 kDa polypeptides is not associated with higher seed methionine concentrations

Suppression of phaseolin and lectin accumulation in common bean resulted in higher concentrations of bean seed polypeptides with apparent molecular weights of 54 kDa and from 70 to 84 kDa on SDS-polyacrylamide gel electrophoresis. Polypeptides of 54 and 56 kDa segregated as products of different alleles. Genes for the 54/56 kDa bands and phaseolin were estimated to be 26.2±3.7 map units apart. The 54 kDa band phenotype manifested by SDS-PAGE consisted of from one to three polypeptides of 54 kDa MW on 2D gels, and the 56 kDa phenotype consisted of one polypeptide of 56 kDa plus two minor polypeptides of 54-54.5 kDa molecular weight. The pK_I of these polypeptides was approximately 5.25. The methionine content of the 54 kDa polypeptides of the cultivar Great Northern Star was 1.6±0.1 g/100 g protein, which was not statistically different from the value (1.5±0.1%) obtained for phaseolin isolated by the same procedure. F₂ seeds deficient for phaseolin and lectin contained as much total N per g as wild-type seeds and were not shrunken, but contained 50% more free amino acids. F₂ seeds from two of the three populations contained from 8 to 13% less methionine per mg total N.     

The potential for rust infection to cause natural selection in apomictic Arabis holboellii (Brassicaceae)

Few studies have examined the potential for pathogens with complex life cycles to cause selection on their required alternate (=intermediate) hosts. Here we examine the effects of two fungal pathogens on an herbaceous mustard, Arabis holboellii. One pathogen species uses A. holboellii as a primary host, the other uses it as an alternate host. This plant-pathogen system is especially interesting because the host, A. holboellii, is apomictic; thus individuals reproduce exact copies of themselves. Despite this mode of reproduction, A. holboellii populations are surprisingly genetically diverse. Could frequency dependent selection by pathogens be maintaining clonal diversity? This study assesses the potential for selection by pathogens. In a controlled greehouse experiment we show that there is heritable variation in A. holboellii's resistance to the rust, Puccinia monoica, and that host fitness is severely reduced by P. monoica infection in both the greenhouse and under natural conditions. Field observations indicate that host clones are also differentially susceptible to the short-cycled rust, P. thlaspeos, and that host fitness is reduced by infection to this pathogen as well. Although the preconditions for pathogen-mediated selection are present, frequency-dependent selection by pathogens is unlikely to be important in structuring populations of Arabis holboellii because multiple host genotypes are susceptible to the same inoculum and the pathogen has a long generation time.     

Adult emergence phenology in checkerspot butterflies: the effects of macroclimate,topoclimate, and population history

The prediction of adult emergence times in insect populations can be greatly complicated by microclimatic gradients, especially in circumstances where distributions of juveniles along those gradients vary from year to year. To investigate adult emergence patterns in topographically heterogeneous habitats, we built a model of postdiapause development of the Bay checkerspot butterfly, Euphydryas editha bayensis. The model uses slope-specific insolation as the rate-controlling variable, and accounts for both solar exposure of the habitat and cloud cover. Instar-specific larval mass gains per unit of insolation were determined from mark-recapture experiments. A small correction for daily low temperatures was used to calibrate the model to five years of field data on larval mass. The model predicted mean mass of 90% of larval samples within 4 clear days over a 70–120 day growing season. The magnitude of spatial variation in emergence times across habitat slopes is greater than annual variation in emergence times due to yearly weather conditions. Historical variation (yearly shifts in larval distributions across slopes) is an important determinant of mean population emergence dates. All of these factors need to be considered in understanding adult emergence phenology in this butterfly and in other insects inhabiting heterogeneous thermal environments. Such an understanding can be useful in managing insect populations for both pest control and conservation.