Genome-Wide Association Studies in an Isolated Founder Population from the Pacific Island of Kosrae

It has been argued that the limited genetic diversity and reduced allelic heterogeneity observed in isolated founder populations facilitates discovery of loci contributing to both Mendelian and complex disease. A strong founder effect, severe isolation, and substantial inbreeding have dramatically reduced genetic diversity in natives from the island of Kosrae, Federated States of Micronesia, who exhibit a high prevalence of obesity and other metabolic disorders. We hypothesized that genetic drift and possibly natural selection on Kosrae might have increased the frequency of previously rare genetic variants with relatively large effects, making these alleles readily detectable in genome-wide association analysis. However, mapping in large, inbred cohorts introduces analytic challenges, as extensive relatedness between subjects violates the assumptions of independence upon which traditional association test statistics are based. We performed genome-wide association analysis for 15 quantitative traits in 2,906 members of the Kosrae population, using novel approaches to manage the extreme relatedness in the sample. As positive controls, we observe association to known loci for plasma cholesterol, triglycerides, and C-reactive protein and to a compelling candidate loci for thyroid stimulating hormone and fasting plasma glucose. We show that our study is well powered to detect common alleles explaining ≥5% phenotypic variance. However, no such large effects were observed with genome-wide significance, arguing that even in such a severely inbred population, common alleles typically have modest effects. Finally, we show that a majority of common variants discovered in Caucasians have indistinguishable effect sizes on Kosrae, despite the major differences in population genetics and environment.     

Potent convulsant actions of the adenosine receptor antagonist, xanthine amine congener (XAC)

The convulsant properties of xanthine amine congener (XAC, 8-(4-(2-aminoethyl)-aminocarboxylmethyloxy)phenyl-1,3-dipropylxant hine) are compared to those of caffeine. Male Swiss albino mice were infused with convulsants through a lateral tail vein. Convulsion thresholds (i.e. the amount of convulsants required to elicit convulsions) of 39.8 +/- 2.0 mg/kg (n = 10) and 109.8 +/- 2.3 mg/kg (n = 10) were calculated for XAC and caffeine respectively. Pretreatment of animals with the adenosine receptor agonists 2-chloroadenosine, N6-cyclohexyladenosine or 5'-N-ethylcarboxamido-adenosine (1 mg/kg, i.p., 20 minutes prior to infusion) significantly decreased the seizure threshold of both XAC and caffeine. The adenosine uptake blockers, 6-nitrobenzylthioinosine or dipyridamole (0.25 mg/kg, i.p., 20 minutes prior to infusion) did not significantly affect the seizure threshold to either XAC or caffeine. The benzodiazepine agonist diazepam (5 mg/kg, i.p., 20 minutes prior to infusion) significantly increased the seizure threshold to both XAC (p less than 0.05) and caffeine (p less than 0.01), whereas the benzodiazepine antagonist Ro 15-1788 (10 mg/kg, i.p., 20 minutes prior to infusion) significantly increased the seizure threshold to caffeine (p less than 0.01), but not XAC. The results suggest that actions at benzodiazepine receptors may be a tenable hypothesis to explain the convulsant actions of caffeine, but not those of XAC.     

Sequence versus Structure for the Direct Detection of 16S rRNA on Planar Oligonucleotide Microarrays

A two-probe proximal chaperone detection system consisting of a species-specific capture probe for the microarray and a labeled, proximal chaperone probe for detection was recently described for direct detection of intact rRNAs from environmental samples on oligonucleotide arrays. In this study, we investigated the physical spacing and nucleotide mismatch tolerance between capture and proximal chaperone detector probes that are required to achieve species-specific 16S rRNA detection for the dissimilatory metal and sulfate reducer 16S rRNAs. Microarray specificity was deduced by analyzing signal intensities across replicate microarrays with a statistical analysis-of-variance model that accommodates well-to-well and slide-to-slide variations in microarray signal intensity. Chaperone detector probes located in immediate proximity to the capture probe resulted in detectable, nonspecific binding of nontarget rRNA, presumably due to base-stacking effects. Species-specific rRNA detection was achieved by using a 22-nt capture probe and a 15-nt detector probe separated by 10 to 14 nt along the primary sequence. Chaperone detector probes with up to three mismatched nucleotides still resulted in species-specific capture of 16S rRNAs. There was no obvious relationship between position or number of mismatches and within- or between-genus hybridization specificity. From these results, we conclude that relieving secondary structure is of principal concern for the successful capture and detection of 16S rRNAs on planar surfaces but that the sequence of the capture probe is more important than relieving secondary structure for achieving specific hybridization.     

Emotion-Motion Interactions in Conversion Disorder: An fMRI Study

Objectives

To evaluate the neural correlates of implicit processing of negative emotions in motor conversion disorder (CD) patients.

Methods

An event related fMRI task was completed by 12 motor CD patients and 14 matched healthy controls using standardised stimuli of faces with fearful and sad emotional expressions in comparison to faces with neutral expressions. Temporal changes in the sensitivity to stimuli were also modelled and tested in the two groups.

Results

We found increased amygdala activation to negative emotions in CD compared to healthy controls in region of interest analyses, which persisted over time consistent with previous findings using emotional paradigms. Furthermore during whole brain analyses we found significantly increased activation in CD patients in areas involved in the ‘freeze response’ to fear (periaqueductal grey matter), and areas involved in self-awareness and motor control (cingulate gyrus and supplementary motor area).

Conclusions

In contrast to healthy controls, CD patients exhibited increased response amplitude to fearful stimuli over time, suggesting abnormal emotional regulation (failure of habituation / sensitization). Patients with CD also activated midbrain and frontal structures that could reflect an abnormal behavioral-motor response to negative including threatening stimuli. This suggests a mechanism linking emotions to motor dysfunction in CD.     

Morphology of the granular secretory glands in skin of poison-dart frogs (Dendrobatidae)

The granular glands of nine species of dendrobatid frogs were examined using light and electron microscopy. The glands are surrounded by a discontinuous layer of smooth muscle cells. Within the glands proper the secretory cells form a true syncytium. Multiple flattened nuclei lie at the periphery of the gland. The peripheral cytoplasm also contains mitochondria, rough surfaced endoplasmic reticulum, the Golgi apparatus, and an abundance of smooth endoplasmic reticulum. Centrally, most of the gland is filled with membrane-bound granules surrounded by amorphous cytoplasm. Few other organelles are found in this region. Early in the secretory cycle, the central part of the gland is filled with flocculent material which appears to be progressively partitioned off by membranes to form the droplet anlage. As granules form, the structure of the contents becomes progressively more vesicular. Dense vesicles, which bud off from the Golgi apparatus, fuse with the granular membrane during the development of granules, and might contain enzymes involved in toxin synthesis. The granules at this point resemble multivesicular bodies. Their structure is similar in all species of dendrobatid frogs even though the different frogs secrete substances of different chemical structure and toxicity.     

An alternative pathway of recombination of chromosomal fragments precedes recA-dependent recombination in the radioresistant bacterium Deinococcus radiodurans.

Deinococcus radiodurans R1 and other members of this genus are able to repair and survive extreme DNA damage induced by ionizing radiation and many other DNA-damaging agents. The ability of R1 to repair completely > 100 double-strand breaks in its chromosome without lethality or mutagenesis is recA dependent. However, during the first 1.5 h after irradiation, recA+ and recA cells show similar increases in the average size of chromosomal fragments. In recA+ cells, DNA continues to enlarge to wild-type size within 29 h. However, in recA cells, no DNA repair is observed following the first 1.5 h postirradiation. This recA-independent effect was studied further, using two slightly different Escherichia coli plasmids forming adjacent duplication insertions in the chromosome, providing repetitive sequences suitable for circularization by non-recA-dependent pathways following irradiation. After exposure to 1.75 Mrad (17,500 Gy), circular derivatives of the integration units were detected in both recA+ and recA cells. These DNA circles were formed in the first 1.5 h postirradiation, several hours before the onset of detectable recA-dependent homologous recombination. By comparison, D. radiodurans strains containing the same E. coli plasmids as nonrepetitive direct insertions did not form circular derivatives of the integration units before or after irradiation in recA+ or recA cells. The circular derivatives of the tandemly integrated plasmids were formed before the onset of recA-dependent repair and have structures consistent with the hypothesis that DNA repair occurring immediately postirradiation is by a recA-independent single-strand annealing reaction and may be a preparatory step for further DNA repair in wild-type D. radiodurans.     

Fatty acid composition of Simonsiella strains

Gas-liquid chromatography of methyl esters of bound fatty acids extracted from the cells of 48 Simonsiella strains showed that these aerobic, gliding, multicellular-filamentous bacteria have fatty acid profiles of the pattern considered typical of Gramnegative eubacteria. All strains contained predominantly tetradecanoic acid (29.5%), 9-hexadecenoic acid (22.2%), an unidentified acid with an equivalent chain length of approximately 20 carbon atoms (15.8%), and dodecanoic acid (11.4%).Discriminant analysis of the mean relative percentages of 12 fatty acids correctly assigned 94% of the strains to groups based on their source of origin (i.e., the oral cavities of sheep, cat, human or dog); the relative amounts of only 3 of the fatty acids (9-octadecenoic acid, hexadecanoic acid, and tetradecanoic acid) provided most of this discrimination.