Biomedical subjects
V Allan
Publications and source records attributed to V Allan.
The endoplasmic reticulum--structure and function (Bristol, September 20-22, 1999).
Explore the source record for details and available documents.
Two kinesin-related proteins associated with the cold-stable cytoskeleton of carrot cells: characterization of a novel kinesin, DcKRP120-2.
We have previously described the biochemical isolation of 65 kDa and 120 kDa microtubule-associated proteins from carrot cytoskeletons. The 65 kDa MAPs have subsequently been shown to be structural MAPs that reconstitute 30 nm cross-bridges of the kind that maintain cortical microtubules in parallel groups. By exploiting its avid binding to microtubules, we have now devised a method for isolating MAP120 from protoplast extracts, and shown that it has properties of a kinesin-related protein. MAP120 segregates with the cold stable pool of microtubules in carrot cytoskeletons, whilst the 65 kDa MAPs are also associated with the cold-sensitive microtubules. On gradient gels, MAP120 resolves as two kinesin-like bands. We report the isolation of a carrot cDNA, DcKRP120-2, corresponding to a novel kinesin of the BimC class known to move to the plus ends of microtubules. Antibodies raised against specific expressed sequences recognize the upper band, while the lower band is recognized by antibodies to the tobacco kinesin-related protein, TKRP125. We have also isolated a partial genomic carrot DNA, DcKRP120-1, homologous to the motor region of tobacco TKRP125. Immunofluorescence of the two proteins produces different staining patterns. Anti-TKRP125 labels the cortical microtubules and the pre-prophase band, but anti-DcKRP120-2 does so only weakly. Both clearly stain the spindle and the phragmoplast, but in a proportion of cells anti-DcKRP120-2 strongly decorates the phragmoplast mid-line where the plus ends of the microtubules overlap. We discuss the potential roles of these proteins during the microtubule cycle.
Corrigendum to: 'Microtubule-based membrane movement'.
Explore the source record for details and available documents.
Microtubule-based membrane movement.
Explore the source record for details and available documents.
Motor proteins: a dynamic duo.
The interactions between the microtubule motor cytoplasmic dynein and its putative regulator dynactin have been shown to be dynamic and complex.
Membrane traffic motors.
There is a wealth of data suggesting that microtubules and associated motor proteins play important roles in orchestrating membrane traffic within higher eukaryotes, with myosins and actin filaments fulfilling similar functions in organisms such as fungi, algae and plants. In addition, evidence is accumulating that both cytoskeletal systems can co-operate within one cell. Recent studies have highlighted how individual motor proteins can act at multiple steps in the membrane-traffic pathways, and in contrast, how more than one motor type may be involved in each transport step and in generating organelle morphology.
Protein phosphatase 1 regulates the cytoplasmic dynein-driven formation of endoplasmic reticulum networks in vitro.
Interphase Xenopus egg extracts form extensive tubular membrane networks in vitro. These networks are identified here as endoplasmic reticulum by the presence of ER resident proteins, as shown by immunofluorescence, and by the presence of single ribosomes and polysomes, as shown by electron microscopy. The effect of phosphorylation on ER movement in interphase was tested using the phosphatase inhibitor, okadaic acid. Okadaic acid treatment resulted in an increase of up to 27-fold in the number of ER tubules moving and in the extent of ER networks formed compared to control extracts. This activation was blocked by the broad-specificity kinase inhibitor 6-dimethylaminopurine. Okadaic acid had no effect, however, on the direction of ER tubule movement, which occurred towards the minus end of microtubules, and was sensitive to low concentrations of vanadate. Inhibition of phosphatases also had no effect on the speed or duration of ER tubule extensions, and did not stimulate the activity of soluble cytoplasmic dynein. The sensitivity of ER movement to okadaic acid closely matched that of protein phosphatase 1. Although the amount of ER motility was greatly increased by inhibiting protein phosphatase 1 (PP1), the amount of cytoplasmic dynein associated with the membrane was not altered. The data support a model in which phosphorylation regulates ER movement by controlling the activity of cytoplasmic dynein bound to the ER membrane.
Organelle movement. Dynactin: portrait of a dynein regulator.
Recent studies of dynactin, a protein complex implicated in regulating the cytoplasmic motor protein dynein, reveal that the complex contains a specialized actin filament and may also interact with microtubules.
Movement of membrane tubules along microtubules in vitro: evidence for specialised sites of motor attachment.
We have studied the microtubule-dependent formation of tubular membrane networks in vitro, using a heterologous system composed of Xenopus egg cytosol combined with rat liver membrane fractions enriched in either Golgi stacks or rough endoplasmic reticulum. The first step in membrane network construction involves the extension of membrane tubules along microtubules by the action of microtubule-based motor proteins. We have observed for both membrane fractions that 80-95% of moving tubule tips possess a distinct globular domain. These structures do not form simply as a consequence of motor protein activity, but are stable domains that appear to be enriched in active microtubule motors. Negative stain electron microscopy reveals that the motile globular domains associated with the RER networks are generally smaller than those observed in networks derived from a crude Golgi stack fraction. The globular domains from the Golgi fraction are often packed with very low density lipoprotein particles (the major secretory product of hepatocytes) and albumin, which suggests that motor proteins may be specifically enriched in organelle regions where proteins for export are accumulated. These data raise the possibility that the concentration of active motor proteins into specialised membrane domains may be an important feature of the secretory pathway.
Clinical and urodynamic features of failed incontinence surgery in the female.
Sixty women with urinary incontinence were treated by the Burch colposuspension operation and bladder neck plication. The pre- and postoperative clinical and urodynamic features of the 15 patients with recurrent incontinence were compared and contrasted with 45 women who were cured. Factors which were associated with failed surgery included increaseing age, previous continence surgery, the presence of detrusor instability, and a postoperative rise of intrinsic bladder pressure either on filling of standing up.
Biofeedback in the treatment of detrusor instability.
Detrusor instability has remained resistant to conventional forms of treatment. An attempt to use biofeedback methods in its management is described. Six female patients with symptoms of frequency, urgency and urge incontinence due to detrusor instability were conditioned to auditory and visual stimuli for 6 to 8 1 h sessions. They were assessed clinically and urodynamically. The results are presented as well as detailed case studies of 3 patients. Subjectively, 3 were cured, 2 improved and 1 remained the same; objectively, 3 were cured, 1 improved and 2 remained the same. No significant side effects were encountered.