Variation in tolerance to drought among Scandinavian populations of <Emphasis Type="Italic">Arabidopsis lyrata</Emphasis>

The ability to cope with water limitation influences plant distributions, and several plant traits have been interpreted as adaptations to drought stress. In Scandinavia, the perennial herb Arabidopsis lyrata occurs in open habitats that differ widely in climate and water availability in summer, suggesting differential selection on drought-related traits. We conducted two greenhouse experiments to examine differentiation in drought response traits among six Scandinavian populations, and to determine whether leaf trichomes confer protection against drought. We quantified tolerance to drought as fitness (survival and biomass of survivors) when exposed to drought relative to fitness under non-drought conditions. Two Swedish populations from shores along the Bothnian Bay had higher tolerance to drought than four riverbed populations from Norway. Under conditions of drought, the shore populations experienced less leaf damage compared to the riverbed populations, and their survival and biomass were less reduced relative to non-drought conditions. Across populations, tolerance to drought was positively related to leaf mass per area and negatively related to flowering propensity and proportion roots, but not related to plant size at the initiation of the drought treatment. In populations polymorphic for trichome production, trichome-producing plants were more tolerant to drought than glabrous plants. The results suggest that both leaf morphology and life-history traits contribute to differential drought response in natural populations of A. lyrata, and that this system offers excellent opportunities for examining the adaptive value and genetic basis of drought-related traits.     

Effect of oxytocin on neuroblastoma cell viability and growth

Oxytocin, released in response to different physiological stimuli, could play a key role in reducing stress reaction. It was suggested that it has protective effect against inflammation and consequences of oxidative stress. Mechanisms how oxytocin effects mediated in the brain tissue are unclear. In this study, oxytocin effect on cell growth and neuronal viability was examined. Human neuroblastoma (SH-SY5Y and SK-N-SH) and glioblastoma (U87MG) cells were exposed to different concentrations of oxytocin for 12-96 h. Potential protective effect of oxytocin treatment was investigated after exposing cells to oxidative stress using hydrogen peroxide (50 mM, 2 h) or 6-hydroxydopamine (25 μM, 24 h). Cell proliferation was measured by cell counting and cell viability was examined by MTT assay. Protein expression of selected neurotrophic factors was measured as an additional parameter. Oxytocin (1 μM) significantly increased cell number in all three cell types. Viability of SH-SY5Y cells was increased in the presence of oxytocin without significant effect of dose (0.01-1 μM). Cell death induced by hydrogen peroxide was not prevented by incubation with oxytocin. Oxytocin pretreatment blunted neurotoxin 6-OHDA reduction of cell viability in SH-SY5Y cells. Oxytocin (1 μM, 12 h) elevated amount of total proteins without increasing levels of brain-derived neurotrophic factor and neurotrophic growth factor. In conclusion, oxytocin increases growth and viability of neuroblastoma and glioblastoma cells without activation of neurotrophic factors. Oxytocin does not have protective effect in oxidative stress; however, it might be important for neuroprotection to dopaminergic neurons. Its proliferative effect might be important in native cell life, euplastic processes, and tumor progression.     

Impact of recombination on polymorphism of genes encoding Kunitz-type protease inhibitors in the genus Solanum

Background

The group of Kunitz-type protease inhibitors (KPI) from potato is encoded by a polymorphic family of multiple allelic and non-allelic genes. The previous explanations of the KPI variability were based on the hypothesis of random mutagenesis as a key factor of KPI polymorphism.

Results

KPI-A genes from the genomes of Solanum tuberosum cv. Istrinskii and the wild species Solanum palustre were amplified by PCR with subsequent cloning in plasmids. True KPI sequences were derived from comparison of the cloned copies. “Hot spots” of recombination in KPI genes were independently identified by DnaSP 4.0 and TOPALi v2.5 software.The KPI-A sequence from potato cv. Istrinskii was found to be 100% identical to the gene from Solanum nigrum. This fact illustrates a high degree of similarity of KPI genes in the genus Solanum. Pairwise comparison of KPI A and B genes unambiguously showed a non-uniform extent of polymorphism at different nt positions. Moreover, the occurrence of substitutions was not random along the strand. Taken together, these facts contradict the traditional hypothesis of random mutagenesis as a principal source of KPI gene polymorphism. The experimentally found mosaic structure of KPI genes in both plants studied is consistent with the hypothesis suggesting recombination of ancestral genes. The same mechanism was proposed earlier for other resistance-conferring genes in the nightshade family (Solanaceae).Based on the data obtained, we searched for potential motifs of site-specific binding with plant DNA recombinases.During this work, we analyzed the sequencing data reported by the Potato Genome Sequencing Consortium (PGSC), 2011 and found considerable inconsistence of their data concerning the number, location, and orientation of KPI genes of groups A and B.

Conclusions

The key role of recombination rather than random point mutagenesis in KPI polymorphism was demonstrated for the first time.     

NS2B/NS3 protease: allosteric effect of mutations associated with the pathogenicity of tick-borne encephalitis virus

The sequences of the protease domain of the tick-borne encephalitis (TBE) virus NS3 protein have two amino acid substitutions, 16 R→K and 45 S→F, in the highly pathogenic and poorly pathogenic strains of the virus, respectively. Two models of the NS2B-NS3 protease complex for the highly pathogenic and poorly pathogenic strains of the virus were constructed by homology modeling using the crystal structure of West Nile virus NS2B-NS3 protease as a template; 20?ns molecular dynamic simulations were performed for both models, the trajectories of the dynamic simulations were compared, and the averaged distance between the two models was calculated for each residue. Conformational differences between two models were revealed in the identified pocket. The different conformations of the pocket resulted in different orientations of the NS2B segment located near the catalytic triad. In the model of the highly pathogenic TBE virus the identified pocket had a more open conformation compared to the poorly pathogenic model. We propose that conformational changes in the active protease center, caused by two amino acid substitutions, can influence enzyme functioning and the virulence of the virus.     

Molecular and Functional Differences between Heart mKv1.7 Channel Isoforms

Ion channels are membrane-spanning proteins that allow ions to permeate at high rates. The kinetic characteristics of the channels present in a cell determine the cell signaling profile and therefore cell function in many different physiological processes. We found that Kv1.7 channels from mouse heart muscle have two putative translation initiation start sites that generate two channel isoforms with different functional characteristics, mKv1.7L (489 aa) and a shorter mKv1.7S (457 aa). The electrophysiological analysis of mKv1.7L and mKv1.7S channels revealed that the two channel isoforms have different inactivation kinetics. The channel resulting from the longer protein (L) inactivates faster than the shorter channels (S). Our data supports the hypothesis that mKv1.7L channels inactivate predominantly due to an N-type related mechanism, which is impaired in the mKv1.7S form. Furthermore, only the longer version mKv1.7L is regulated by the cell redox state, whereas the shorter form mKv1.7S is not. Thus, expression starting at each translation initiation site results in significant functional divergence. Our data suggest that the redox modulation of mKv1.7L may occur through a site in the cytoplasmic N-terminal domain that seems to encompass a metal coordination motif resembling those found in many redox-sensitive proteins. The mRNA expression profile and redox modulation of mKv1.7 kinetics identify these channels as molecular entities of potential importance in cellular redox-stress states such as hypoxia.     

高密度种群的社会条件对大沙鼠幼年雄鼠形态生理特征的影响:一个实例研究

在非繁殖期高密度大沙鼠(RhombomysopimusLicht)种群中,我们研究了胁迫以及幼年雄鼠的性激素浓度、腹中腺大小和体重对社群中成体(≥1年龄)存在的依赖性。用无损伤放射免疫方法,测定了于1999年秋天在野外采集的幼年雄鼠粪便样品的皮质酮和睾酮。有成体社群中的个体大于无成体社群的个体。因此,成体对幼体的影响不能独立于社群大小本身。成体的存在促进粪便睾酮的浓度和抑制了幼年雄鼠的性成熟(由雄激素依赖的较小的腹中腺来估计),但是同时促进了其生长。因此,自然存在的社群环境能影响幼年雄鼠的形态生理特征发育。