The mutation of the LEW.1AR1-<Emphasis Type="Italic">iddm</Emphasis> rat maps to the telomeric end of rat chromosome 1

The LEW.1AR1-iddm rat is an animal model of human type 1 diabetes mellitus (T1DM) with an autosomal recessive mode of inheritance. T1DM susceptibility loci could be localized on chromosome (RNO) 20 in the major histocompatibility complex region (Iddm1) and on RNO1 (Iddm8, Iddm9) in a BN backcross cohort. In this study the impact of the different susceptibility regions on diabetes development was investigated in a backcross population of the diabetes-resistant PAR strain. A cohort of 130 [(PAR × LEW.1AR1-iddm) × LEW.1AR1-iddm] N2 rats was monitored for blood glucose and analyzed by linkage analysis. Sixteen percent of the PAR backcross animals developed T1DM. Genetic analysis revealed significant linkage to T1DM in the MHC region on RNO20p12. In contrast to the linkage analysis of the BN backcross cohort, only one susceptibility locus for T1DM could be identified on RNO1. This susceptibility region on RNO1 mapped to the telomeric end corresponding to Iddm8. Eighty-nine percent of diabetic PAR backcross animals were homozygous for Iddm8. The Iddm9 diabetes susceptibility region showed no linkage to diabetes in the PAR backcross cohort. The data of this study provide evidence that the mutation leading to T1DM in the LEW.1AR1-iddm rat is located at the telomeric end of RNO1 corresponding to Iddm8. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. H. Weiss and T. Arndt contributed equally to this study.     

Clinicopathologic factors and nuclear morphometry as independent prognosticators in KIT-positive gastrointestinal stromal tumors.

Gastrointestinal stromal tumors (GISTs) are mesenchymal neoplasms found in the gastrointestinal tract. The purpose of this study was to evaluate whether morphometric measurements could complement tumor size and mitotic activity in risk evaluation. Nuclear roundness and ellipse axis ratio were found to correlate with tumor size, mitotic activity, nuclear atypia, and hemorrhage. Morphometric variables in 422 GISTs were significant for overall survival in univariate analyses but did not retain independent significance in multivariate analyses incorporating mitotic count and tumor size. Traditional variables, together with sex, location of primary tumor, and nuclear atypia, seem to be the best parameters for prognostic evaluation.     

Is there plasticity in developmental instability? The effect of daily thermal fluctuations in an ectotherm

Diversified bet‐hedging (DBH) by production of within‐genotype phenotypic variance may evolve to maximize fitness in stochastic environments. Bet‐hedging is generally associated with parental effects, but phenotypic variation may also develop throughout life via developmental instability (DI). This opens for the possibility of a within‐generation mechanism creating DBH during the lifetime of individuals. If so, DI could in fact be a plastic trait itself; if a fluctuating environment indicates uncertainty about future conditions, sensing such fluctuations could trigger DI as a DBH response. However, this possibility has received little empirical attention. Here, we test whether fluctuating environments may elicit such a response in the clonally reproducing crustacean Daphnia magna. Specifically, we exposed genetically identical individuals to two environments of different thermal stability (stable vs. pronounced daily realistic temperature fluctuations) and tested for effects on DI in body mass and metabolic rate shortly before maturation. Furthermore, we also estimated the genetic variation in DI. Interestingly, fluctuating temperatures did not affect body mass, but metabolic rate decreased. We found no evidence for plasticity in DI in response to environmental fluctuations. The lack of plasticity was common to all genotypes, and for both traits studied. However, we found considerable evolvability for DI, which implies a general evolutionary potential for DBH under selection for increased phenotypic variance.     

Identification and characterization of novel PKA holoenzymes in human T lymphocytes

Cyclic AMP-dependent protein kinase (PKA) is a holoenzyme that consists of a regulatory (R) subunit dimer and two catalytic (C) subunits that are released upon stimulation by cAMP. Immunoblotting and immunoprecipitation of T-cell protein extracts, immunofluorescence of permeabilized T cells and RT/PCR of T-cell RNA using C subunit-specific primers revealed expression of two catalytically active PKA C subunits C alpha1 (40 kDa) and C beta2 (47 kDa) in these cells. Anti-RI alpha and Anti-RII alpha immunoprecipitations demonstrated that both C alpha1 and C beta2 associate with RI alpha and RII alpha to form PKAI and PKAII holoenzymes. Moreover, Anti-C beta2 immunoprecipitation revealed that C alpha1 coimmunoprecipitates with C beta2. Addition of 8-CPT-cAMP which disrupts the PKA holoenzyme, released C alpha1 but not C beta2 from the Anti-C beta2 precipitate, indicating that C beta2 and C alpha1 form part of the same holoenzyme. Our results demonstrate for the first time that various C subunits may colocate on the same PKA holoenzyme to form novel cAMP-responsive enzymes that may mediate specific effects of cAMP.     

Genetic variation and structure in the expanding moss Pogonatum dentatum (Polytrichaceae) in its area of origin and in a recently colonized area

Genetic variation in the expanding moss species Pogonatum dentatum was studied using intersimple sequence repeat (ISSR) markers. The genetic consequences of range expansion were studied by comparing source populations in a mountain area with populations from a recently colonized lowland area in Sweden. Indices of genetic variation show slightly lower number of alleles per locus in the lowlands and a similar gene diversity in both areas. Three of four lowland populations had evidence of a recently passed bottleneck. Considerably higher haplotype diversity was found in the recently colonized lowlands compared to source populations in the mountains. Patterns of allelic diversity suggest that P. dentatum experiences loss of genetic variation through founder effects and genetic drift when expanding its distribution range. Higher haplotypic diversity, less linkage disequilibrium, and fewer compatible loci indicate that sexual recombination is relatively more important in the lowlands compared to the mountains. A likely explanation is higher success of establishment from spores in the lowlands, while clonal propagation predominates in the mountains. Less genetic differentiation among lowland populations indicates more gene flow in the lowland area, involving more spores and/or fragments moving among populations.     

Molecular cloning of KLRI1 and KLRI2, a novel pair of lectin-like natural killer-cell receptors with opposing signalling motifs

We here report the molecular cloning of a novel family of killer-cell lectin-like (KLR) receptors in the rat and the mouse, termed KLRI. In both species, there are two members, KLRI1 and KLRI2. While the extracellular lectin-like domains of KLRI1 and KLRI2 are similar [74% (rat) and 83% (mouse) amino acid identity], they differ intracellularly. KLRI1 has two immunoreceptor tyrosine-based inhibition motifs (ITIMs) in the cytoplasmic domain, suggesting an inhibitory function. KLRI2 has no ITIM, but a positively charged lysine residue in the transmembrane region, suggesting association with activating adapter molecules. Klri1 and Klri2 are localized within the natural killer (NK) cell gene complex on rat chromosome 4 and mouse chromosome 6. By RT-PCR and Northern blot analysis KLRI1 and KLRI2 were selectively expressed by NK cells in both rat and mouse. Epitope-tagged expression constructs of rat KLRI1 and rat KLRI2 induced surface expression of a nondisulphide-linked protein of M_r 36,000/39,000 and M_r 34,000, respectively.     

Egg-size evolution in aquatic environments: does oxygen availability constrain size?

Selection against large eggs has been proposed for aquatic environments, putatively because large eggs should have more difficulty obtaining the required oxygen. Here, we use brown trout (Salmo trutta) eggs to provide an experimental test of this hypothesis. At high levels of dissolved oxygen (14 mg l(-1)), egg survival was high and independent of egg size. At low oxygen levels (2.3 mg l(-1)), survival decreased overall, and was higher for large-egged than small-egged siblings. Thus, contrary to conventional expectation, low oxygen levels selected for large rather than small eggs. A second experiment using Atlantic salmon (S. salar) eggs indicated that oxygen consumption increases relatively slowly with increasing egg mass (allometric constant = 0.44). The failure of the conventional 'bigger is worse during incubation' hypothesis may thus be due to the erroneous assumption that oxygen consumption increases at a greater rate with increasing egg mass than does the egg surface area that is available for oxygen diffusion. We also demonstrate, using data from Atlantic salmon, that nest-specific oxygen consumption decreases with increasing egg size, but that this effect is more pronounced for large than for small females. This may help to explain the positive correlation between adult body size and egg size observed in fishes that cluster their eggs.     

Interactions between spermine and Mg2+ on mitochondrial Ca2+ transport

The effects of the polyamine spermine on the regulation of Ca2+ transport by subcellular organelles from rat liver, heart, and brain were investigated using ion-sensitive minielectrodes and a 45Ca2+ tracer method. Spermine stimulated Ca2+ uptake by mitochondria but not by microsomes. In the presence of spermine, isolated mitochondria could maintain a free extramitochondrial Ca2+ concentration of 0.3-0.2 microM. Stimulation of the initial rates of Ca2+ uptake and 45Ca2+ cycling of mitochondria by spermine shows that this was accomplished through a decrease of the apparent Km for Ca2+ uptake by the Ca2+ uniporter. The half maximally effective concentration of spermine (50 microM) was in the range of physiological concentrations of this polyamine in the cell. Spermidine was five times less effective. Putrescine was ineffective. The stimulation of mitochondrial Ca2+ uptake by spermine was inhibited by Mg2+ in a concentration-dependent manner. However, the diminished contribution of the mitochondria to the regulation of the free extraorganellar Ca2+ concentration could mostly be compensated for by microsomal Ca2+ uptake. Spermine also reversed ruthenium red-induced Ca2+ efflux from mitochondria. It is concluded that spermine is an activator of the mitochondrial Ca2+ uniporter and Mg2+ an antagonist. By this mechanism, the polyamines can confer to the mitochondria an important role in the regulation of the free cytoplasmic Ca2+ concentration in the cell and of the free Ca2+ concentration in the mitochondrial matrix.