Selective Association (selective + association)

Distribution by Scientific Domains

Selected Abstracts

SYMPOSIUM REVIEW: Lipid microdomains and the regulation of ion channel function

Caroline Dart
Many types of ion channel localize to cholesterol and sphingolipid-enriched regions of the plasma membrane known as lipid microdomains or ,rafts'. The precise physiological role of these unique lipid microenvironments remains elusive due largely to difficulties associated with studying these potentially extremely small and dynamic domains. Nevertheless, increasing evidence suggests that membrane rafts regulate channel function in a number of different ways. Raft-enriched lipids such as cholesterol and sphingolipids exert effects on channel activity either through direct protein,lipid interactions or by influencing the physical properties of the bilayer. Rafts also appear to selectively recruit interacting signalling molecules to generate subcellular compartments that may be important for efficient and selective signal transduction. Direct interaction with raft-associated scaffold proteins such as caveolin can also influence channel function by altering gating kinetics or by affecting trafficking and surface expression. Selective association of ion channels with specific lipid microenvironments within the membrane is thus likely to be an important and fundamental regulatory aspect of channel physiology. This brief review highlights some of the existing evidence for raft modulation of channel function. [source]

Temporal and selective association of multiple sigma factors with RNA polymerase during sporulation in Bacillus subtilis

GENES TO CELLS, Issue 2 2000
Masaya Fujita
Background During sporulation in Bacillus subtilis, an asymmetric division produces two cells, a forespore and mother cell, with which follow different developmental paths. The highly ordered programme of temporal and spatial gene activation during sporulation is governed by the principal RNA polymerase holoenzyme (E,A) and alternative holoenzyme forms containing the developmental sigma factors ,H, ,F, ,E, ,G and ,K, which appear successively during development. The control mechanism(s) of temporal and selective association of multiple sigma factors with core RNA polymerase is unclear. As a first step to addressing these issues, this report quantifies the amount of each subunit of RNA polymerase that is present in the sporangium during sporulation, and analyses in vitro the relative affinities of each sigma subunit for core RNA polymerase. Results Using quantitative immunoblot analysis, the amounts of E,A, E,H, E,E and E,K in relation to the total amount of RNA polymerase at appropriate time-points were found to be 15%, 1%, 6% and 2%, respectively. Therefore, the core RNA polymerase is predicted to be in excess. The level of core RNA polymerase and ,A remained constant during the transition from vegetative growth to sporulation, whereas the sporulation-specific sigma factors appeared successively, in the order ,H, ,E and ,K. Competition experiments between sigma factors in an in vitro transcription system revealed the dominance of ,A over ,H and ,E for open promoter complex formation. These results are inconsistent with the idea that late appearing sigma factors can displace earlier appearing sigmas from the core enzyme. Conclusions As the core RNA polymerase is in excess, the results suggest that successive sigma factors can bind to core RNA polymerase without having to displace earlier appearing sigma factors. Thus, the programme of gene expression during sporulation might not require mechanisms for the substitution of one sigma factor by another on the core RNA polymerase. [source]

A disconnection account of Gerstmann syndrome: Functional neuroanatomy evidence,

Elena Rusconi PhD
Objective To examine the functional neuroanatomy that could account for pure Gerstmann syndrome, which is the selective association of acalculia, finger agnosia, left-right disorientation, and agraphia. Methods We used structural and functional neuroimaging at high spatial resolution in healthy subjects to seek a shared cortical substrate of the Grundstörung posited by Gerstmann, ie, a common functional denominator accounting for this clinical tetrad. We construed a functional activation paradigm that mirrors each of the four clinical deficits in Gerstmann syndrome and determined cortical activation patterns. We then applied fiber tracking to diffusion tensor images and used cortical activation foci in the four functional domains as seed regions. Results None of the subjects showed parietal overlap of cortical activation patterns from the four cognitive domains. In every subject, however, the parietal activation patterns across all four domains consistently connected to a small region of subcortical parietal white matter at a location that is congruent with the lesion in a well-documented case of pure Gerstmann syndrome. Interpretation Our functional neuroimaging findings are not in agreement with Gerstmann's postulate of damage to a common cognitive function underpinning clinical semiology. Our evidence from intact functional neuroanatomy suggests that pure forms of Gerstmann's tetrad do not arise from lesion to a shared cortical substrate but from intraparietal disconnection after damage to a focal region of subcortical white matter. Ann Neurol 2009;66:654,662 [source]

Phenylhydrazine as a partial model for ,-thalassaemia red blood cell hemodynamic properties

Yuval Ramot
Summary ,-Thalassaemia is a congenital haemoglobinopathy, associated with red blood cells (RBC) anomalies, leading to impairment of their flow-affecting properties, namely, RBC deformability, self-aggregability, and adherence to endothelial cells (EC). Treatment of normal RBC with phenylhydrazine (PHZ) causes selective association of oxidized ,-globin chains with the membrane skeleton, leading to reduced RBC deformability, characteristic of ,-thalassaemia. PHZ has thus been used to mimic phenotypes of ,-thalassaemia RBC. The present study was undertaken to further elucidate the suitability of PHZ-treated RBC as a model for ,-thalassemic RBC, by comparing the aggregability and adhesiveness of PHZ-treated RBC to those of RBC from thalassaemia intermedia (TI) patients, using image analysis of RBC under flow. In addition, the externalization of phosphatidylserine (PS), a mediator of RBC/EC interaction, was determined. It was found that PHZ caused enhanced RBC adhesiveness to extracellular matrix, similar to TI-RBC. Furthermore, in both conditions, the enhanced adhesiveness was mediated by PS translocated to the RBC surface. In contrast, PHZ treatment completely abolished RBC aggregability, while TI-RBC aggregability was slightly elevated. It is proposed that PHZ-treated RBC resemble ,-thalassaemia RBC in their deformability and adhesiveness, but not in their aggregability, and thus can be used as a limited model for ,-thalassaemia RBC phenotypes. [source]