Pathogenomics

The genomes described this month reflect the overall historical bias of microbial genomics towards pathogenic bacteria. Although the balance is now being redressed to some extent, especially through the study of extremophiles, it is still the case that the opportunities provided by genomic studies are primarily taken up by those who study bacterial pathogenicity. This part of the field is, however, being broadened by including the study of pathogens of animals, insects and plants alongside those that afflict humans.     

Quantitative assessment of IgG antibodies to Helicobacter pylori and outcome of ischaemic heart disease

Criticisms of serological studies on Helicobacter pylori and ischaemic heart disease (IHD) include: undiagnosed heart disease in live controls; no assessment of severity or outcome of IHD; and qualitative not quantitative measurements of IgG to the bacteria. The aim was to assess quantitatively IgG levels specific for H. pylori (ng ml(-1)) among patients who survived a myocardial infarction (MI) with those who died of IHD. Sera were from four groups: (1) men who survived one MI; (2) men matched for age and socioeconomic background to group 1; (3) individuals who died suddenly of IHD; (4) accidental deaths matched for age and sex to group 3. Levels of IgG to H. pylori increased with age (P<0.005) but were not associated with smoking or socioeconomic groups. There was a correlation between IgG to the bacteria and decreasing socioeconomic levels only among group 1 (P<0.01). IgG levels were higher for subjects who died of heart disease (median=151 ng ml(-1)) compared with survivors (median=88 ng ml(-1)) (P=0.034) and higher for survivors compared with their controls (median=58 ng ml(-1)) (P=0.039). Future serological studies of H. pylori in relation to IHD should be quantitative and severity of disease considered in analyses.     

Making scents of sex underwater

Sex and scents have long been associated. Musk, for example, is a sexual scent that has been used for many years in the perfume industry. In humans, the debate on the existence of sex pheromones continues, whereas in insects their role is well known. Through recent research, we are discovering that such chemicals are equally important in conveying sexual signals between aquatic animals.     

Lack of gonadotrophin-releasing hormone (GnRH) neuron response to decreasing photoperiod in thyroidectomized male starlings (Sturnus vulgaris)

Exposure of starlings to long days initially causes reproductive maturation, but eventually leads to photorefractoriness. During photorefractoriness, gonadotrophin-releasing hormone (GnRH) decreases in the GnRH cell bodies and fibers emanating from these to the median eminence, circulating gonadotrophin concentrations decrease to a minimum, and the gonads regress. Thyroidectomy profoundly affects these photoperiodic responses. In chronically thyroidectomized starlings, gonadal responses to changes in day length are attenuated. This investigation was conducted to determine whether, in the absence of gonadal responsiveness, the GnRH system of chronically thyroidectomized starlings responds to changes in day length. Two groups of thyroidectomized male starlings were transferred from short days (8L:16D) to long days (18L:6D) for four weeks, and testicular volume increased. One group was kept on long days (TxLD) and the other was returned to short days (TxSD). Testicular volume did not decrease in the TxSD group. The GnRH neurons of the two thyroidectomized groups were compared to those of two groups of intact starlings, one of them on long days and photorefractory (ILD), the other on short days and photosensitive (ISD). Group ILD had lower numbers of GnRH-stained cells than groups TxLD, TxSD and ISD, which did not differ in this respect. Similar differences were observed for GnRH cell size in the pre-optic area (POA) and for density of staining of GnRH fibers in the median eminence. The results confirm that thyroidectomy attenuates gonadal responses to change in day length and suggest that this results from an effect upon the central nervous system rather than a peripheral effect.     

Targeted recovery of mutations in Drosophila

Reverse genetic techniques will be necessary to take full advantage of the genomic sequence data for Drosophila and other experimental organisms. To develop a method for the targeted recovery of mutations, we combined an EMS chemical mutagenesis regimen with mutation detection by denaturing high performance liquid chromatography (DHPLC). We recovered mutant strains at the high rate of approximately 4.8 mutations/kb for every 1000 mutagenized chromosomes from a screen for new mutations in the Drosophila awd gene. Furthermore, we observed that the EMS mutational spectrum in Drosophila germ cells shows a strong preference for 5'-PuG-3' sites, and for G/C within a stretch of three or more G/C base pairs. Our method should prove useful for targeted mutagenesis screens in Drosophila and other genetically tractable organisms and for more precise studies of mutagenesis and DNA repair mechanisms.     

Individual vocal recognition and the effect of partial lesions to HVc on discrimination, learning, and categorization of conspecific song in adult songbirds

Among songbirds, the capacity to associate particular songs with particular singers (i.e., vocal recognition) forms the cognitive basis for more complex communication behaviors such as female choice and territoriality. In the present study, we combine operant conditioning techniques and excitotoxic lesions to the forebrain nucleus HVc to examine the role of this region in the discrimination, associative learning, and categorization of conspecific song. We trained adult male and female European starlings, Sturnus vulgaris, to recognize simultaneously the songs of several conspecific males. Then, using a series of transfer procedures, we demonstrate that correct recognition does not generalize to song bouts containing novel motifs from familiar singers. This suggests that starlings do not make use of individually invariant source or filter characteristics for vocal recognition. We then lesioned a portion of HVc bilaterally with ibotenic acid, and exposed the birds to a series of manipulations testing the discrimination, associative learning, and categorization of conspecific song. The lesions attenuated song production among males, but retention of the basic recognition task (i.e., maintenance of the discrimination) was unaffected. However, when the response contingencies were reversed-as a test of associative learning independent of discrimination-the initial performance and subsequent learning rate were negatively correlated with the size of the HVc lesions. This suggests that HVc plays a role in the formation of associations between a song and some referent. The results of this study are discussed in light of earlier claims regarding the role of HVc in the perceptual processing of conspecific song.     

Selective and Genetic Constraints on Pneumococcal Serotype Switching

Streptococcus pneumoniae isolates typically express one of over 90 immunologically distinguishable polysaccharide capsules (serotypes), which can be classified into “serogroups” based on cross-reactivity with certain antibodies. Pneumococci can alter their serotype through recombinations affecting the capsule polysaccharide synthesis (cps) locus. Twenty such “serotype switching” events were fully characterised using a collection of 616 whole genome sequences from systematic surveys of pneumococcal carriage. Eleven of these were within-serogroup switches, representing a highly significant (p < 0.0001) enrichment based on the observed serotype distribution. Whereas the recombinations resulting in between-serogroup switches all spanned the entire cps locus, some of those that caused within-serogroup switches did not. However, higher rates of within-serogroup switching could not be fully explained by either more frequent, shorter recombinations, nor by genetic linkage to genes involved in β–lactam resistance. This suggested the observed pattern was a consequence of selection for preserving serogroup. Phenotyping of strains constructed to express different serotypes in common genetic backgrounds was used to test whether genotypes were physiologically adapted to particular serogroups. These data were consistent with epistatic interactions between the cps locus and the rest of the genome that were specific to serotype, but not serogroup, meaning they were unlikely to account for the observed distribution of capsule types. Exclusion of these genetic and physiological hypotheses suggested future work should focus on alternative mechanisms, such as host immunity spanning multiple serotypes within the same serogroup, which might explain the observed pattern.     

Assessing Depression Related Severity and Functional Impairment: The Overall Depression Severity and Impairment Scale (ODSIS)

Background

The Overall Depression Severity and Impairment Scale (ODSIS) is a brief, five-item measure for assessing the frequency and intensity of depressive symptoms, as well as functional impairments in pleasurable activities, work or school, and interpersonal relationships due to depression. Although this scale is expected to be useful in various psychiatric and mental health settings, the reliability, validity, and interpretability have not yet been fully examined. This study was designed to examine the reliability, factorial, convergent, and discriminant validity of a Japanese version of the ODSIS, as well as its ability to distinguish between individuals with and without a major depressive disorder diagnosis.

Methods

From a pool of registrants at an internet survey company, 2830 non-clinical and clinical participants were selected randomly (619 with major depressive disorder, 619 with panic disorder, 576 with social anxiety disorder, 645 with obsessive–compulsive disorder, and 371 non-clinical panelists). Participants were asked to respond to the ODSIS and conventional measures of depression, functional impairment, anxiety, neuroticism, satisfaction with life, and emotion regulation.

Results

Exploratory and confirmatory factor analysis of three split subsamples indicated the unidimensional factor structure of ODSIS. Multi-group confirmatory factor analysis showed invariance of factor loadings between non-clinical and clinical subsamples. The ODSIS also showed excellent internal consistency and test–retest intraclass correlation coefficients. Convergence and discriminance of the ODSIS with various measures were in line with our expectations. Receiver operating characteristic curve analyses showed that the ODSIS was able to detect a major depressive syndrome accurately.

Conclusions

This study supports the reliability and validity of ODSIS in a non-western population, which can be interpreted as demonstrating cross-cultural validity.     

α-Synuclein Delays Endoplasmic Reticulum (ER)-to-Golgi Transport in Mammalian Cells by Antagonizing ER/Golgi SNAREs

Toxicity of human α-synuclein when expressed in simple organisms can be suppressed by overexpression of endoplasmic reticulum (ER)-to-Golgi transport machinery, suggesting that inhibition of constitutive secretion represents a fundamental cause of the toxicity. Whether similar inhibition in mammals represents a cause of familial Parkinson''s disease has not been established. We tested elements of this hypothesis by expressing human α-synuclein in mammalian kidney and neuroendocrine cells and assessing ER-to-Golgi transport. Overexpression of wild type or the familial disease-associated A53T mutant α-synuclein delayed transport by up to 50%; however, A53T inhibited more potently. The secretory delay occurred at low expression levels and was not accompanied by insoluble α-synuclein aggregates or mistargeting of transport machinery, suggesting a direct action of soluble α-synuclein on trafficking proteins. Co-overexpression of ER/Golgi arginine soluble N-ethylmaleimide-sensitive factor attachment protein receptors (R-SNAREs) specifically rescued transport, indicating that α-synuclein antagonizes SNARE function. Ykt6 reversed α-synuclein inhibition much more effectively than sec22b, suggesting a possible neuroprotective role for the enigmatic high expression of ykt6 in neurons. In in vitro reconstitutions, purified α-synuclein A53T protein specifically inhibited COPII vesicle docking and fusion at a pre-Golgi step. Finally, soluble α-synuclein A53T directly bound ER/Golgi SNAREs and inhibited SNARE complex assembly, providing a potential mechanism for toxic effects in the early secretory pathway.