Adaptive Remodelling by FliN in the Bacterial Rotary Motor

Sensory adaptation in the Escherichia coli chemosensory pathway has been the subject of interest for decades, with investigation focusing on the receptors that process extracellular inputs. Recent studies demonstrate that the flagellar motors responsible for cell locomotion also play a role, adding or subtracting FliM subunits to maximise sensitivity to pathway signals. It is difficult to reconcile this FliM remodelling with the observation that partner FliN subunits are relatively static fixtures in the motor. By fusing a fluorescent protein internally to FliN, we show that there is in fact significant FliN remodelling. The kinetics and stoichiometry of FliN in steady state and in adapting motors are investigated and found to match the behaviour of FliM in all respects except for timescale where FliN rates are about 4 times slower. We notice that motor adaptation is slower in the presence of the fluorescent protein, indicating a possible source for the difference. The behaviour of FliM and FliN is consistent with a kinetic and stoichiometric model that contradicts the traditional view of a packed, rigid motor architecture.     

Interrelationship between Cytoplasmic Retroviral Gag Concentration and Gag–Membrane Association

The early events in the retrovirus assembly pathway, particularly the timing and nature of Gag translocation from the site of protein translation to the inner leaflet of the plasma membrane, are poorly understood. We have investigated the interrelationship between cytoplasmic Gag concentration and plasma membrane association using complementary live-cell biophysical fluorescence techniques in real time with both human T-cell leukemia virus type 1 (HTLV-1) and human immunodeficiency virus type 1 (HIV-1) Gag proteins. In particular, dual-color, z-scan fluorescence fluctuation spectroscopy in conjunction with total internal reflection fluorescence and conventional, epi-illumination imaging were utilized. Our results demonstrate that HTLV-1 Gag is capable of membrane targeting and particle assembly at low (i.e., nanomolar) cytoplasmic concentrations and that there is a critical threshold concentration (approaching micromolar) prior to the observation of HIV-1 Gag associated with the plasma membrane. These observations imply fundamental differences between HIV-1 and HTLV-1 Gag trafficking and membrane association.     

Molecular Characterization of Various Trichomonad Species Isolated from Humans and Related Mammals in Indonesia

Trichomonad species inhabit a variety of vertebrate hosts; however, their potential zoonotic transmission has not been clearly addressed, especially with regard to human infection. Twenty-one strains of trichomonads isolated from humans (5 isolates), pigs (6 isolates), rodents (6 isolates), a water buffalo (1 isolate), a cow (1 isolate), a goat (1 isolate), and a dog (1 isolate) were collected in Indonesia and molecularly characterized. The DNA sequences of the partial 18S small subunit ribosomal RNA (rRNA) gene or 5.8S rRNA gene locus with its flanking regions (internal transcribed spacer region, ITS1 and ITS2) were identified in various trichomonads; Simplicimonas sp., Hexamastix mitis, and Hypotrichomonas sp. from rodents, and Tetratrichomonas sp. and Trichomonas sp. from pigs. All of these species were not detected in humans, whereas Pentatrichomonas hominis was identified in humans, pigs, the dog, the water buffalo, the cow, and the goat. Even when using the high-resolution gene locus of the ITS regions, all P. hominis strains were genetically identical; thus zoonotic transmission between humans and these closely related mammals may be occurring in the area investigated. The detection of Simplicimonas sp. in rodents (Rattus exulans) and P. hominis in water buffalo in this study revealed newly recognized host adaptations and suggested the existence of remaining unrevealed ranges of hosts in the trichomonad species.     

Amplified fragment length polymorphisms,the evolution of the land snail genus Theba (Stylommatophora: Helicidae), and an objective approach for relating fossils to internal nodes of a phylogenetic tree using geometric morphometrics

Time‐trees are commonly calibrated based on fossils attributed to internal nodes, thus defining the minimum age of these nodes. However, in the absence of synapomorphies, the phylogenetic position of a fossil can only be inferred based on similarity. In this study, we objectively allocated fossil shells to internal nodes based on the reconstruction of ancestral shapes and sizes in a geometric morphometric framework. Our phylogenetic analysis of 24 (putative sub)species was based on 2524 amplified fragment length polymorphism loci. In this well‐supported tree the taxa occurring in north‐west Africa and on the Iberian peninsula were paraphyletic with respect to the (sub)species from the Canary and Selvagen Islands, indicating a continental origin of the genus in contrast to our earlier sequence‐based account. Ancestral shell shapes and sizes were inferred based on landmark data using squared‐change parsimony. In a subsequent principal component analysis, only three of 20 fossil shells could be unequivocally allocated to internal nodes. However, these fossils were all Quaternary, and thus too young to infer meaningfully narrow confidence intervals for divergence estimates that probably reach back into the Miocene or even Oligocene. The apparent failure of allocating older fossils to internal nodes and achieving a reliable tree calibration was caused by the absence of phylogenetic signal in the shells of Theba due to extensive, sometimes rapid, convergent evolution, including reversals. © 2014 The Linnean Society of London     

The role of MAPK signalling pathways in the response to endoplasmic reticulum stress

Perturbations in endoplasmic reticulum (ER) homeostasis, including depletion of Ca^2 + or altered redox status, induce ER stress due to protein accumulation, misfolding and oxidation. This activates the unfolded protein response (UPR) to re-establish the balance between ER protein folding capacity and protein load, resulting in cell survival or, following chronic ER stress, promotes cell death. The mechanisms for the transition between adaptation to ER stress and ER stress-induced cell death are still being understood. However, the identification of numerous points of cross-talk between the UPR and mitogen-activated protein kinase (MAPK) signalling pathways may contribute to our understanding of the consequences of ER stress. Indeed, the MAPK signalling network is known to regulate cell cycle progression and cell survival or death responses following a variety of stresses. In this article, we review UPR signalling and the activation of MAPK signalling pathways in response to ER stress. In addition, we highlight components of the UPR that are modulated in response to MAPK signalling and the consequences of this cross-talk. We also describe several diseases, including cancer, type II diabetes and retinal degeneration, where activation of the UPR and MAPK signalling contribute to disease progression and highlight potential avenues for therapeutic intervention. This article is part of a Special Issue entitled: Calcium Signaling In Health and Disease. Guest Editors: Geert Bultynck, Jacques Haiech, Claus W. Heizmann, Joachim Krebs, and Marc Moreau.     

Evidence for species-specific clock gene expression patterns in hamster peripheral tissues

Rhythmic oscillations that repeat every 24 h can be found in numerous behavioral and physiological functions. Beside the endogenous master clock in the suprachiasmatic nucleus (SCN), peripheral oscillators exist that can disengage from the master clock rhythm by different mechanisms. The fact that core clock genes in peripheral tissues do not always have the same characteristics as in the SCN suggests that their function may vary in different organs. Additionally, suggestions about species-specific variation in expression peak and nadir times, especially in the testis, led to the need for systematical investigations on clock gene expression patterns in different organs and species under standardized methodological conditions. Therefore, daily gene expression patterns of the clock genes Bmal1, Period1, Period2, Clock, Cryptochrome1 and Cryptochrome2 were recorded at each of eight time points during a 24 hour period in the testis, kidney, liver, spleen and heart of three hamster species (Phodopus sungorus, Phodopus roborovskii and Cricetulus griseus; family: Cricetidae). Clock gene expression was found to be rhythmic in all investigated organs, however with inconsistent results in the testis. Complex cosinor analysis revealed species differences in temporal gene expression patterns regarding their orthophase, number of peaks, and amplitude for all genes and organs with most pronounced differences in the testis. The results of this study strongly indicate that clock gene expression in peripheral tissues is species-specific and that their functions might be at least partly connected to clock-unrelated traits that vary between the investigated species. Further studies should aim at clarifying the specific roles of clock genes in the testis.     

生物节律基因Timeless的生物学功能研究进展

Timeless基因广泛分布于生物体中,是主要的生物节律基因之一,它通过与节律基因Per和Cry家族成员的相互作用影响它们的表达水平。Timeless和Tipin能够稳定复制叉,促进姊妹染色单体凝聚,对DNA复制有促进作用;在细胞周期中激活S期检测点,参与ATR-Chk1和ATM-Chk2的DNA损伤修复通路,加强细胞周期的阻滞以修复DNA损伤。Timeless是生物节律和细胞周期的连接者,在多种癌组织(如肝癌、肺癌、乳腺癌、结直肠癌、肾癌和胰腺癌)中的表达水平与癌旁非癌组织相比有差异,提示Timeless表达异常可能与肿瘤的发生和发展相关。     

Long‐term changes in hypoxia and soluble reactive phosphorus in the hypolimnion of a large temperate lake: consequences of a climate regime shift

The (Lower) Lake of Zurich provides an ideal system for studying the long‐term impact of environmental change on deep‐water hypoxia because of its sensitivity to climatic forcing, its history of eutrophication and subsequent oligotrophication, and the quality and length of its data set. Based on 39 years (1972–2010) of measured profiles of temperature, oxygen concentration and phosphorus (P) concentration, the potentially confounding effects of oligotrophication and climatic forcing on the occurrence and extent of deep‐water hypoxia in the lake were investigated. The time‐series of Nürnberg's hypoxic factor (HF) for the lake can be divided into three distinct segments: (i) a segment of consistently low HF from 1972 to the late‐1980s climate regime shift (CRS); (ii) a transitional segment between the late‐1980s CRS and approximately 2000 within which the HF was highly variable; and (iii) a segment of consistently high HF thereafter. The increase in hypoxia during the study period was not a consequence of a change in trophic status, as the lake underwent oligotrophication as a result of reduced external P loading during this time. Instead, wavelet analysis suggests that changes in the lake's mixing regime, initiated by the late‐1980s CRS, ultimately led to a delayed but abrupt decrease in the deep‐water oxygen concentration, resulting in a general expansion of the hypoxic zone in autumn. Even after detrending to remove long‐term effects, the concentration of soluble reactive P in the bottom water of the lake was highly correlated with various measures of hypoxia, providing quantitative evidence supporting the probable effect of hypoxia on internal P loading. Such climate‐induced, ecosystem‐scale changes, which may result in undesirable effects such as a decline in water quality and a reduction in coldwater fish habitats, provide further evidence for the vulnerability of large temperate lakes to predicted increases in global air temperature.     

Cell‐wall invertases,key enzymes in the modulation of plant metabolism during defence responses

Most plant–pathogen interactions do not result in pathogenesis because of pre‐formed defensive plant barriers or pathogen‐triggered activation of effective plant immune responses. The mounting of defence reactions is accompanied by a profound modulation of plant metabolism. Common metabolic changes are the repression of photosynthesis, the increase in heterotrophic metabolism and the synthesis of secondary metabolites. This enhanced metabolic activity is accompanied by the reduced export of sucrose or enhanced import of hexoses at the site of infection, which is mediated by an induced activity of cell‐wall invertase (Cw‐Inv). Cw‐Inv cleaves sucrose, the major transport sugar in plants, irreversibly yielding glucose and fructose, which can be taken up by plant cells via hexose transporters. These hexose sugars not only function in metabolism, but also act as signalling molecules. The picture of Cw‐Inv regulation in plant–pathogen interactions has recently been broadened and is discussed in this review. An interesting emerging feature is the link between Cw‐Inv and the circadian clock and new modes of Cw‐Inv regulation at the post‐translational level.