The role of the FtsA protein in Bacillus subtilis cell division

University of Technology, Sydney. Faculty of Science.Bacterial cell division involves the invagination of the membrane and the cell wall to form a septum at midcell, between two replicated chromosomes. From a molecular perspective, the main event in cell division is the formation of a circumferential structure, the Z ring, formed by polymerisation of the tubulin-like FtsZ protein. The Z ring recruits a multi-protein complex to the division site, forming a division apparatus that eventually constricts as the septum forms. FtsA, a eukaryotic actin homologue, is another division protein, known to interact directly with FtsZ. It has been proposed that FtsA promotes Z ring formation; however its exact role has remained unknown. This thesis investigateshow FtsA affects the Z ring and cytokinesis in the Gram-positive model organism, Bacillus subtilis. Interestingly, FtsA is essential in Escherichia coli, the Gram-negative model organism, but not in Bacillus subtilis. Rather, deletion of the ftsA gene in vegetatively-growing B. subtilis cells causes a significant reduction in Z ring formation and cell division is severely diminished while cell growth is maintained, resulting in cell filamentation (long cells without septa). To confirm that this phenotype is due to the inability of FtsZ to efficiently form rings, Z ring formationwas examined in the absence of FtsA, during the first round of cell division following B. subtilis spore germination. Surprisingly the Z rings formed with wild-type efficiency. However, unlike wild-type cells that showed subsequent constriction of these Z rings leading to septum formation, Z rings did not constrict immediately in the ftsA mutant and persisted into the second cycle of division. These results reveal for the first time that, unlike E. coli, FtsA is not required for Z ring formation in B. subtilis. To understand the delay in Z ring constriction, further experiments were conducted to determine if the recruitment of downstream division proteins to the Z ring is affectedin the absence of FtsA. The live-cell microscopy data confirmed that the recruitment of DivIB, and presumably other downstream division proteins that are co-recruited with DivIB, is delayed in ftsA-mutant cells, but occurs with wild-type efficiency. However, after recruitment of DivIB, Z ring constriction and septation are still inefficient in the absence of FtsA. These observations indicate a primary role for FtsA in B. subtilis in the later stages of division, that is, after the division apparatus has assembled. This work reveals a novel perspective on the function of this protein. In an attempt to further explore how Z ring constriction is affected by FtsA, microscopy studies were designed to analyse this cell process. Different Z ring constriction defects were observed in ftsA-mutant cells. Importantly, it was shown that, in the absence of FtsA, constriction is either significantly delayed or never occurs, resulting in destabilisation of the Z ring, indicating that FtsA is required for efficient Z ring constriction in B. subtilis. This finding raised the possibility that FtsA may be affecting the dynamics of the Z ring during cytokinesis. To verify this, the rate of FtsZ turnover in Z rings of ftsA-mutant cells was investigated. The results demonstrated a decrease in the rate of the FtsZ turnover in the Z ring in the absence of FtsA, possibly enough to cause an effect on Z ring constriction

Increased expression of miR-187 in human islets from individuals with type 2 diabetes is associated with reduced glucose-stimulated insulin secretion

Journal ArticleThis article is published with open access at Springerlink.com Electronic supplementary material. The online version of this article (doi:10.1007/s00125-013-3089-4) contains peer-reviewed but unedited supplementary material, which is available to authorised usersAims/hypothesis: Type 2 diabetes is characterised by progressive beta cell dysfunction, with changes in gene expression playing a crucial role in its development. MicroRNAs (miRNAs) are post-transcriptional regulators of gene expression and therefore alterations in miRNA levels may be involved in the deterioration of beta cell function. Methods: Global TaqMan arrays and individual TaqMan assays were used to measure islet miRNA expression in discovery (n = 20) and replication (n = 20) cohorts from individuals with and without type 2 diabetes. The role of specific dysregulated miRNAs in regulating insulin secretion, content and apoptosis was subsequently investigated in primary rat islets and INS-1 cells. Identification of miRNA targets was assessed using luciferase assays and by measuring mRNA levels. Results: In the discovery and replication cohorts miR-187 expression was found to be significantly increased in islets from individuals with type 2 diabetes compared with matched controls. An inverse correlation between miR-187 levels and glucose-stimulated insulin secretion (GSIS) was observed in islets from normoglycaemic donors. This correlation paralleled findings in primary rat islets and INS-1 cells where overexpression of miR-187 markedly decreased GSIS without affecting insulin content or apoptotic index. Finally, the gene encoding homeodomain-interacting protein kinase-3 (HIPK3), a known regulator of insulin secretion, was identified as a direct target of miR-187 and displayed reduced expression in islets from individuals with type 2 diabetes. Conclusions/interpretation: Our findings suggest a role for miR-187 in the blunting of insulin secretion, potentially involving regulation of HIPK3, which occurs during the pathogenesis of type 2 diabetes. © 2013 The Author(s).This work was supported by the Wellcome Trust (project grant number 089845/Z/09/Z). GAR is the recipient of Royal Society Wolfson Research and Wellcome Trust Senior Investigator (WT098424AIA) Awards, and thanks the Medical Research Council (MRC) for Programme Grant MR/J0003042/1. GdSX and GAR were supported by a project grant from Diabetes UK (BDA 13/0004672) and HDR by MRC grant G1001644

Comparison of DeLorme with Oxford resistance training techniques: effects of training on muscle damage markers

Aim: The purpose of this study was comparing DeLorme with Oxford methods through ten repetition maximum (10 RM) performance and serum creatine kinase (CK) and lactate dehydrogenase (LDH) activity. Methods: Before and after four weeks of training with the DEL (n=16) or OXF (n=16) resistance training (RT) methods, rest and post exercise serum CK activity, serum LDH activity and 10 RM performance were measured and compared. Results: Both methods provide higher 10 RM results after training without significant differences between groups (p<0.05). Rest and post exercise CK and LDH activity was less after training with DeLorme (DEL) and Oxford (OXF), but the magnitude of the relative peak response (48-hr our 72-hr post exercise, respectively) was higher after each training protocol. Comparisons of CK activity between groups display non-significant differences. Conclusion: DEL or OXF training methods cause the same improvement on muscle performance and both alters CK activity without differences between methods in a 4-week RT program

Evaluation of vineyard growth under four irrigation regimes using vegetation and soil on-the-go sensors

Precision agriculture is a useful tool to assess plant growth and development in vineyards. The present study focused on spatial and temporal analysis of vegetation growth variability, in four irrigation treatments with four replicates. The research was carried out in a vineyard located in the southwest of Spain during the 2012 and 2013 growing seasons. Two multispectral sensors mounted on an all-terrain vehicle (ATV) were used in the different growing seasons/stages in order to calculate the vineyard normalized difference vegetation index (NDVI). Soil apparent electrical conductivity (ECa) was also measured up to 0.8m soil depth using an on-the-go geophysical sensor. All measured data were analysed by means of principal component analysis (PCA). The spatial and temporal NDVI and ECa variations showed relevant differences between irrigation treatments and climatological conditions

Dark spinor models in gravitation and cosmology

We introduce and carefully define an entire class of field theories based on non-standard spinors. Their dominant interaction is via the gravitational field which makes them naturally dark; we refer to them as Dark Spinors. We provide a critical analysis of previous proposals for dark spinors noting that they violate Lorentz invariance. As a working assumption we restrict our analysis to non-standard spinors which preserve Lorentz invariance, whilst being non-local and explicitly construct such a theory. We construct the complete energy-momentum tensor and derive its components explicitly by assuming a specific projection operator. It is natural to next consider dark spinors in a cosmological setting. We find various interesting solutions where the spinor field leads to slow roll and fast roll de Sitter solutions. We also analyse models where the spinor is coupled conformally to gravity, and consider the perturbations and stability of the spinor.Comment: 43 pages. Several new sections and details added. JHEP in prin

The role of the van der Waals interactions in the adsorption of anthracene and pentacene on the Ag(111) surface

Using first-principles calculations based on density-functional theory (DFT), we investigated the effects of the van der Waals (vdW) interactions on the structural and electronic properties of anthracene and pentacene adsorbed on the Ag(111) surface. We found that the inclusion of vdW corrections strongly affects the binding of both anthracene/Ag(111) and pentacene/Ag(111), yielding adsorption heights and energies more consistent with the experimental results than standard DFT calculations with generalized gradient approximation (GGA). For anthracene/Ag(111) the effect of the vdW interactions is even more dramatic: we found that “pure” DFT-GGA calculations (without including vdW corrections) result in preference for a tilted configuration, in contrast to the experimental observations of flat-lying adsorption; including vdW corrections, on the other hand, alters the binding geometry of anthracene/Ag(111), favoring the flat configuration. The electronic structure obtained using a self-consistent vdW scheme was found to be nearly indistinguishable from the conventional DFT electronic structure once the correct vdW geometry is employed for these physisorbed systems. Moreover, we show that a vdW correction scheme based on a hybrid functional DFT calculation (HSE) results in an improved description of the highest occupied molecular level of the adsorbed molecules

The Underestimation Of Egocentric Distance: Evidence From Frontal Matching Tasks

There is controversy over the existence, nature, and cause of error in egocentric distance judgments. One proposal is that the systematic biases often found in explicit judgments of egocentric distance along the ground may be related to recently observed biases in the perceived declination of gaze (Durgin & Li, Attention, Perception, & Psychophysics, in press), To measure perceived egocentric distance nonverbally, observers in a field were asked to position themselves so that their distance from one of two experimenters was equal to the frontal distance between the experimenters. Observers placed themselves too far away, consistent with egocentric distance underestimation. A similar experiment was conducted with vertical frontal extents. Both experiments were replicated in panoramic virtual reality. Perceived egocentric distance was quantitatively consistent with angular bias in perceived gaze declination (1.5 gain). Finally, an exocentric distance-matching task was contrasted with a variant of the egocentric matching task. The egocentric matching data approximate a constant compression of perceived egocentric distance with a power function exponent of nearly 1; exocentric matches had an exponent of about 0.67. The divergent pattern between egocentric and exocentric matches suggests that they depend on different visual cues