The dynamin-related GTPase Dnm1 controls mitochondrial morphology in yeast. Here we show that dnm1 mutations convert the mitochondrial compartment into a planar 'net' of interconnected tubules. We propose that this net morphology results from a defect in mitochondrial fission. Immunogold labelling localizes Dnm1 to the cytoplasmic face of constricted mitochondrial tubules that appear to be dividing and to the ends of mitochondrial tubules that appear to have recently completed division. The activity of Dnm1 is epistatic to that of Fzo1, a GTPase in the outer mitochondrial membrane that regulates mitochondrial fusion. dnm1 mutations prevent mitochondrial fragmentation in fzo1 mutant strains. These findings indicate that Dnm1 regulates mitochondrial fission, assembling on the cytoplasmic face of mitochondrial tubules at sites at which division will occur.The mitochondrion is a complex organelle with a double membrane, its own genome and an independent protein-synthetic machinery. Although the role of mitochondria in metabolism and ATP production is more widely recognized, alterations in mitochondrial shape and abundance are also important for cellular function and differentiation. For example, mitochondrial morphology and copy number change in response to nutrient availability in yeast cells 1 , cell damage and apoptosis in mammalian cells 2 and developmental cues in Xenopus and Drosophila 3,4 . Cytological studies indicate that the 'steady-state' mitochondrial morphology and copy number can vary dramatically in different cell types, ranging from multiple, spherical organelles to the branched, tubular networks found in budding yeast and some mammalian cells [5][6][7] . These differences in mitochondrial morphology and copy number are largely determined by the balance between ongoing mitochondrial fission and fusion events.Little is known about molecules that regulate mitochondrial fission and fusion. The fuzzy onions (fzo) family of transmembrane GTPases was recently shown to control mitochondrial fusion in different organisms and cell types. In Drosophila, fzo is required for a developmentally regulated mitochondrial fusion event during spermatogenesis 8 . In budding yeast, mutations in fzo1 cause mitochondrial networks to fragment 9,10 and prevent mitochondrial fusion during yeast mating 9 . Molecules required for mitochondrial fission © 1999 Macmillan Magazines Ltd § Correspondence and requests for materials should be addressed to J.M.S. shaw@bioscience.utah.edu. NIH Public Access Results Mitochondrial membranes form nets in dnm1 mutant cellsWe previously reported that mitochondrial membranes collapse to one side of the cell in a dnm1Δ mutant strain 11 . Transmission electron microscopy indicated that these collapsed membranes might be organized in an unusual structure 11 . To characterize this structure further, we studied mitochondrial morphology in dnm1Δ cells under several different conditions.As reported previously, dnm1Δ mutants grown at 25 °C lack the highly branched mitochondrial network charac...

Although a pilot, this study has produced a wealth of data that demonstrates the impact of pressure ulcers on people. While a larger study is required to obtain a European perspective, it is still reasonable to conclude that the issues of pain and restrictions should be considered in the development of pressure ulcer treatment and prevention guidelines.

A hydropolymer dressing (Tielle) and a hydrocolloid dressing (Granuflex) were compared In a randomised controlled clinical study involving 100 patients with leg ulcers and 99 patients with pressure sores in the community. Statistically significant differences in favour of the hydropolymer dressing were detected for dressing leakage and odour production, but no statistically significant differences were recorded in the number of patients with either leg ulcers or pressure sores who healed in each treatment group.

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A report of a study that evaluated the performance of Lyofoam A, compared with NA dressing and Tegaderm in treating superficial pressure sores.

This study compared a polyurethane foam dressing with a hydrocolloid dressing for ease of application and removal, adhesion, conformability, absorbency and wear time. A randomised study was carried out, including 61 patients with stage two or three pressure sores in five centres in the UK. Dressings were applied for up to 30 days and assessments were carried out at each dressing change. The results indicated that both dressings are easy and convenient to apply; absorbency and ease of removal were significantly better with the polyurethane foam dressing than the hydrocolloid dressing; wear times were similar.

This study investigated the influence on the number of pressure sores developing in patients nursed in a hospice when three levels of pressure support were used in association with a risk assessment tool. The study was designed as phase one of an epidemiological study examining the use of a modified Norton scoring system. This was followed by a second phase of the study, when patients were allocated to pressure sore support systems according to their risk assessment score. A total of 327 patients entered, 223 in phase one and 104 in phase two. A significant reduction in the development of pressure sores was observed in the second phase of the study.