Is osmotic potential a more appropriate property than electrical conductivity for evaluating whole-plant response to salinity?

Studies of whole-plant or crop responses to salinity often focus on yield or growth reduction in terms of solution ion concentration or electrical conductivity. The response functions describing salt stress may be better presented in terms of solution osmotic potential. We looked at the effect of increasing concentrations of NaCl and CaCl₂, either alone or in equinormal combination, on three different plant species: bean (Phaseolus vulgaris L.), corn (Zea mays L.) and melon (Cucumis melo L.). Corn and melon were found to be relatively tolerant and beans more sensitive to salinity. When yield response was related to the electrical charge concentration of the salts, i.e. salinity was expressed in units of mequiv. L^?1 or electrical conductivity, the stress effects of Na and Ca appeared to be of different magnitudes: plant growth was more sensitive to excess Na than to excess Ca and the effect of combined Na and Ca was intermediate. The effects of the two salts were, however, indistinguishable when salinity was expressed in terms of osmotic potential of the water. For all three species, the response curves of yield as a function of level of equipotential solutions of NaCl, CaCl₂ or combinations of the two salts practically overlapped. Presentation and interpretation of the whole-plant salinity response in terms of osmotic potential would be beneficial in attempts to differentiate between the osmotic and toxic effects of salinity, in normalizing data sets and in increasing their relevance in practical applications.     

Dystrophin deficiency in Drosophila reduces lifespan and causes a dilated cardiomyopathy phenotype

A number of studies have been conducted recently on the model organism Drosophila to determine the function of genes involved in human disease, including those implicated in neurological disorders, cancer and metabolic and cardiovascular diseases. The simple structure and physiology of the Drosophila heart tube together with the available genetics provide a suitable in vivo assay system for studying cardiac gene functions. In our study, we focus on analysis of the role of dystrophin (Dys) in heart physiology. As in humans, the Drosophila dys gene encodes multiple isoforms, of which the large isoforms ( DLPs ) and a truncated form ( Dp117 ) are expressed in the adult heart. Here, we show that the loss of dys function in the heart leads to an age-dependent disruption of the myofibrillar organization within the myocardium as well as to alterations in cardiac performance. dys RNAi-mediated knockdown in the mesoderm also shortens lifespan. Knockdown of all or deletion of the large isoforms increases the heart rate by shortening the diastolic intervals (relaxation phase) of the cardiac cycle. Morphologically, loss of the large DLPs isoforms causes a widening of the cardiac tube and a lower fractional shortening, a phenotype reminiscent of dilated cardiomyopathy. The dilated dys mutant phenotype was reversed by expressing a truncated mammalian form of dys ( Dp116 ). Our results illustrate the utility of Drosophila as a model system to study dilated cardiomyopathy and other muscular-dystrophy-associated phenotypes.     

Ethnic groups and high sensitivity C-reactive protein in Israel

High-sensitivity C-reactive protein (hs-CRP) is a biomarker that correlates with atherothrombotic risk and outcome. hs-CRP is influenced by various modifiable and non-modifiable factors. We studied the relationship between ethnic background and hs-CRP level, among the Jewish population in Israel. A total of 3659 men and 2180 women were divided into two ethnic groups (Ashkenazi and Sephardic Jews), based on the knowledge of Jewish immigration patterns throughout the centuries. Mean hs-CRP levels were calculated for each group and were adjusted for various factors known to influence hs-CRP. Sephardic Jews were found to have higher adjusted mean hs-CRP levels (2.0 mg l^-1 for men and 3.9 mg l^-1 for women) compared with Ashkenazi Jews (1.5 mg l^-1 for men and 2.9 mg l^-1 for women). Ethnic background emerged as an independent significant predictor of hs-CRP levels. We demonstrated that ethnicity is an important factor when considering hs-CRP as a marker of atherothrombotic risk.     

Discerning the ancestry of European Americans in genetic association studies

European Americans are often treated as a homogeneous group, but in fact form a structured population due to historical immigration of diverse source populations. Discerning the ancestry of European Americans genotyped in association studies is important in order to prevent false-positive or false-negative associations due to population stratification and to identify genetic variants whose contribution to disease risk differs across European ancestries. Here, we investigate empirical patterns of population structure in European Americans, analyzing 4,198 samples from four genome-wide association studies to show that components roughly corresponding to northwest European, southeast European, and Ashkenazi Jewish ancestry are the main sources of European American population structure. Building on this insight, we constructed a panel of 300 validated markers that are highly informative for distinguishing these ancestries. We demonstrate that this panel of markers can be used to correct for stratification in association studies that do not generate dense genotype data.     

Can hungry nestlings be trained to reduce their begging?

Nestling begging behavior is usually characterized by a behavioralresponse of increasing begging levels with an increase in nestlingneed or hunger. Recent evidence for the possible effect of learningon begging intensity raises the question of how learning canshape this response rule. In particular, it is not clear whetherhungry nestlings can learn to reduce their begging when it isnot successful or, rather, whether they must first acquire positiveexperiences with low begging levels in order to do so. To explorethis question, we conducted 3 hand-feeding experiments withpairs of house sparrow (Passer domesticus) nestlings. In thefirst 2 experiments, the nestlings targeted to lower their beggingwere rewarded mainly or only for low begging postures. However,despite the high expected reward for low begging, these nestlingsdid not lower their begging. Controlled by their behavioralresponse function, hungry nestlings were "stuck" at high postureswithout being able to experience the potential success of lowpostures. In the third experiment, nestlings targeted to lowertheir begging levels were rewarded for any begging posture,ensuring that satiation would provide their initial "positiveexperience" with low begging postures. Begging postures werereduced by this treatment. In light of these results, we suggestthat parents are unlikely to reduce offspring begging levelsby simply ignoring them. However, they might be able to do soby attending to the begging as soon as possible, thereby allowingtheir offspring to explore low begging and learn that it issufficiently effective. Received 12 April 2007; revised 1 September 2007; accepted 1 October 2007.     

Dynamic length regulation of sensory stereocilia

Stereocilia, the mechanosensory organelles of hair cells, are a distinctive class of actin-based cellular protrusions with an unparalleled ability to regulate their lengths over time. Studies on actin turnover in stereocilia, as well as the identification of several deafness-related proteins essential for proper stereocilia structure and function, provide new insights into the mechanisms and molecules involved in stereocilia length regulation and long-term maintenance. Comparisons of ongoing investigations on stereocilia with studies on other actin protrusions offer new opportunities to further understand common principles for length regulation, the diversity of its mechanisms, and how the specific needs of each cell are met.     

Neutrality of foreign complex subunits in an experimental model of lateral gene transfer

Lateral gene transfer (LGT) is a powerful force in microbial evolution. However, the barriers that restrict this evolutionary phenomenon are not fully understood. It has long been observed that genes that encode subunits of complexes exhibit relatively compatible phylogenies, implying mostly vertical evolution. This may be explained by the failure of a new gene product to effectively interact with preexisting protein subunits, making its acquisition neutral--a theory termed the "complexity hypothesis." On the other hand, such genes may reduce the fitness of the host by disturbing the stoichiometric balance between complex subunits, resulting in purifying selection against gene retention. To examine these 2 alternative scenarios, we designed an experimental system that mimics the transfer of genes encoding homologs of essential complex subunits into the model bacterium Escherichia coli. In addition, we overexpressed the native E. coli gene in order to examine the contribution of gene dosage effects. We show that accumulation of native or foreign complex subunits in the cell does not result in loss of fitness, except for a minor fitness reduction observed for a single foreign homolog. Indeed, a series of genetic and biochemical assays failed to detect any interaction between the foreign subunits and the native polypeptides of the complex, implying an inability of such transfer events to generate positive selection for gene retention. We conclude that LGT of complex subunits may be mostly neutral and that forces operating against gene retention appear to be moderate.