Determinants of Slow Walking Speed in Ambulatory Patients Undergoing Maintenance Hemodialysis

Walking ability is significantly lower in hemodialysis patients compared to healthy people. Decreased walking ability characterized by slow walking speed is associated with adverse clinical events, but determinants of decreased walking speed in hemodialysis patients are unknown. The purpose of this study was to identify factors associated with slow walking speed in ambulatory hemodialysis patients. Subjects were 122 outpatients (64 men, 58 women; mean age, 68 years) undergoing hemodialysis. Clinical characteristics including comorbidities, motor function (strength, flexibility, and balance), and maximum walking speed (MWS) were measured and compared across sex-specific tertiles of MWS. Univariate and multivariate logistic regression analyses were performed to examine whether clinical characteristics and motor function could discriminate between the lowest, middle, and highest tertiles of MWS. Significant and common factors that discriminated the lowest and highest tertiles of MWS from other categories were presence of cardiac disease (lowest: odds ratio [OR] = 3.33, 95% confidence interval [CI] = 1.26–8.83, P<0.05; highest: OR = 2.84, 95% CI = 1.18–6.84, P<0.05), leg strength (OR = 0.62, 95% CI = 0.40–0.95, P<0.05; OR = 0.57, 95% CI = 0.39–0.82, P<0.01), and standing balance (OR = 0.76, 95% CI = 0.63–0.92, P<0.01; OR = 0.81, 95% CI = 0.68–0.97, P<0.05). History of fracture (OR = 3.35, 95% CI = 1.08–10.38; P<0.05) was a significant factor only in the lowest tertile. Cardiac disease, history of fracture, decreased leg strength, and poor standing balance were independently associated with slow walking speed in ambulatory hemodialysis patients. These findings provide useful data for planning effective therapeutic regimens to prevent decreases in walking ability in ambulatory hemodialysis patients.     

An Atypical Tubulin Kinase Mediates Stress-Induced Microtubule Depolymerization in Arabidopsis

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Embryonic Medaka Model of Microglia in the Developing CNS Allowing In Vivo Analysis of Their Spatiotemporal Recruitment in Response to Irradiation

Radiation therapy (RT) is pivotal in the treatment of many central nervous system (CNS) pathologies; however, exposure to RT in children is associated with a higher risk of secondary CNS tumors. Although recent research interest has focused on the reparative and therapeutic role of microglia, their recruitment following RT has not been elucidated, especially in the developing CNS. Here, we investigated the spatiotemporal dynamics of microglia during tissue repair in the irradiated embryonic medaka brain by whole-mount in situ hybridization using a probe for Apolipoprotein E (ApoE), a marker for activated microglia in teleosts. Three-dimensional imaging of the distribution of ApoE-expressing microglia in the irradiated embryonic brain clearly showed that ApoE-expressing microglia were abundant only in the late phase of phagocytosis during tissue repair induced by irradiation, while few microglia expressed ApoE in the initial phase of phagocytosis. This strongly suggests that ApoE has a significant function in the late phase of phagocytosis by microglia in the medaka brain. In addition, the distribution of microglia in p53-deficient embryos at the late phase of phagocytosis was almost the same as in wild-type embryos, despite the low numbers of irradiation-induced apoptotic neurons, suggesting that constant numbers of activated microglia were recruited at the late phase of phagocytosis irrespective of the extent of neuronal injury. This medaka model of microglia demonstrated specific recruitment after irradiation in the developing CNS and could provide a useful potential therapeutic strategy to counteract the detrimental effects of RT.     

A Theoretical Model of Jigsaw-Puzzle Pattern Formation by Plant Leaf Epidermal Cells

Plant leaf epidermal cells exhibit a jigsaw puzzle–like pattern that is generated by interdigitation of the cell wall during leaf development. The contribution of two ROP GTPases, ROP2 and ROP6, to the cytoskeletal dynamics that regulate epidermal cell wall interdigitation has already been examined; however, how interactions between these molecules result in pattern formation remains to be elucidated. Here, we propose a simple interface equation model that incorporates both the cell wall remodeling activity of ROP GTPases and the diffusible signaling molecules by which they are regulated. This model successfully reproduces pattern formation observed in vivo, and explains the counterintuitive experimental results of decreased cellulose production and increased thickness. Our model also reproduces the dynamics of three-way cell wall junctions. Therefore, this model provides a possible mechanism for cell wall interdigitation formation in vivo.     

Vacuolar and cytoskeletal dynamics during elicitor-induced programmed cell death in tobacco BY-2 cells

Responses of plant cells to environmental stresses often involve morphological changes, differentiation and redistribution of various organelles and cytoskeletal network. Tobacco BY-2 cells provide excellent model system for in vivo imaging of these intracellular events. Treatment of the cell cycle-synchronized BY-2 cells with a proteinaceous oomycete elicitor, cryptogein, induces highly synchronous programmed cell death (PCD) and provide a model system to characterize vacuolar and cytoskeletal dynamics during the PCD. Sequential observation revealed dynamic reorganization of the vacuole and actin microfilaments during the execution of the PCD. We further characterized the effects cryptogein on mitotic microtubule organization in cell cycle-synchronized cells. Cryptogein treatment at S phase inhibited formation of the preprophase band, a cortical microtubule band that predicts the cell division site. Cortical microtubules kept their random orientation till their disruption that gradually occurred during the execution of the PCD twelve hours after the cryptogein treatment. Possible molecular mechanisms and physiological roles of the dynamic behavior of the organelles and cytoskeletal network in the pathogenic signal-induced PCD are discussed.Key words: actin microfilament, cell cycle, cryptogein, microtubules, nuclei, programmed cell death, tobacco BY-2 cells, vacuoles     

Outward-rectifying K+ channel activities regulate cell elongation and cell division of tobacco BY-2 cells

Potassium ions (K⁺) are required for plant growth and development, including cell division and cell elongation/expansion, which are mediated by the K⁺ transport system. In this study, we investigated the role of K⁺ in cell division using tobacco BY-2 protoplast cultures. Gene expression analysis revealed induction of the Shaker -like outward K⁺ channel gene, NTORK1 , under cell-division conditions, whereas the inward K⁺ channel genes NKT1 and NtKC1 were induced under both cell-elongation and cell-division conditions. Repression of NTORK1 gene expression by expression of its antisense construct repressed cell division but accelerated cell elongation even under conditions promoting cell division. A decrease in the K⁺ content of cells and cellular osmotic pressure in dividing cells suggested that an increase in cell osmotic pressure by K⁺ uptake is not required for cell division. In contrast, K⁺ depletion, which reduced cell-division activity, decreased cytoplasmic pH as monitored using a fluorescent pH indicator, SNARF-1. Application of K⁺ or the cytoplasmic alkalizing reagent (NH₄)₂SO₄ increased cytoplasmic pH and suppressed the reduction in cell-division activity. These results suggest that the K⁺ taken up into cells is used to regulate cytoplasmic pH during cell division.     

Quantitative analysis of microtubule orientation in interdigitated leaf pavement cells

Leaf pavement cells are shaped like a jigsaw puzzle in most dicotyledon species. Molecular genetic studies have identified several genes required for pavement cells morphogenesis and proposed that microtubules play crucial roles in the interdigitation of pavement cells. In this study, we performed quantitative analysis of cortical microtubule orientation in leaf pavement cells in Arabidopsis thaliana. We captured confocal images of cortical microtubules in cotyledon leaf epidermis expressing GFP-tubulinβ and quantitatively evaluated the microtubule orientations relative to the pavement cell growth axis using original image processing techniques. Our results showed that microtubules kept parallel orientations to the growth axis during pavement cell growth. In addition, we showed that immersion treatment of seed cotyledons in solutions containing tubulin polymerization and depolymerization inhibitors decreased pavement cell complexity. Treatment with oryzalin and colchicine inhibited the symmetric division of guard mother cells.