Pelvic stresses in vitro--II. A study of the efficacy of metal-backed acetabular prostheses

Six embalmed human cadaveric hemi-pelves with their associated proximal femurs have been tested in vitro using 25 strain-gauge rosettes on each hemi-pelvis. Loads were applied up to 2.5 kN and principal stresses were computed from the principal strain data. Acetabular prostheses, cemented in place upon a cartilage-devoid but intact subchondral bone-plate, showed little change in stress-patterns when compared with the normal data, regardless of whether or not the component employed metal-backing. The use of 30 anchoring holes of 6.4 mm diameter, in the intact subchondral bone-plate, had little effect upon the stress-patterns, regardless of whether metal-backing was employed upon the prosthesis. When the subchondral bone-plate was removed, there were notable changes in the stress-pattern in the periacetabular region and on the medial wall of pelvis. The metal-backed prosthesis did not produce such notable changes as its plastic counterpart, when the subchondral bone-plate was removed. The use of a plastic prosthesis cemented in a Protrusio ring, in an acetabulum devoid of subchondral bone, produced notable changes in the stress-patterns in the whole periacetabular region and on the medial wall.     

Myxosporean infections in cultured tilapias in Israel

Five new species of myxosporean parasite are described from cultured tilapias in Israel. These are: Myxosoma sarigi, Myxosoma equatorialis, Myxobolus israelensis, Myxobolus agolus, and Myxobolus galilaeus. The first four were found in hybrids of Oreochromis aureus X Oreochromis niloticus while Myxobolus galilaeus was found in Sarotherodon galilaeus. In addition, M. sarigi, M. israelensis, and Myxobolus sp. were also found in S. galilaeus. In the light of the present study, the taxonomy of myxosporean infections in tilapias is modified. Mature spores may localize in the melano-macrophage centers of the spleen and kidney where they may eventually be destroyed. No cases of mortality have so far been associated with these parasites.     

Hormonal regulation of iron-stress response in sunflower roots: a morphological and cytological investigation

Summary Sunflowers are known to respond to Fe deficiency (-Fe) with a typical root tip swelling and the formation of root hairs and transfer cells in the rhizodermis. The possible regulation of this process was examined by a comparative study of root morphology and cytology of intact seedlings (Helianthus annuus L. cv. Giganteus) under -Fe and hormonal treatment in nutrient solution. Longitudinal sections of -Fe roots showed root tip swelling is due to cessation of cell elongation and isodiarnetric volume increase of the cortical cells. Enhanced cell division in the pericycle leads to the formation of lateral root primordia in the swollen zone. Xylem vessel differentiation is markedly accelerated and accompanied by early differentiation of the casparian band in the endodermis. Exogenous application of IAA (10^–8-10^–7 M) via the nutrient solution to Fe sufficient plants causes symptoms which closely mimick the characteristics of Fe deficiency including root hair development. Moreover, rhizodermal cells produce peripheral protuberances reminiscent of -Fe transfer cells. Ethylene-releasing ethephon (10^–4M) also causes subapical swelling and root hair formation. However, wall protuberance development is less pronounced. ABA (10^–5 M) leads to similar root thickening and root hair formation but without any comparable transfer cell differentiation. From the striking similarities between -Fe and IAA treatment it is concluded that this hormone (possibly in cooperation with ethylene) is involved in the Fe stress response of sunflower roots. The importance of a continuous polar IAA transport for this process is discussed.Abbreviations ABA abscisic acid - ACC 1-aminocyclopropane-1-carboxylic acid - Ethephone 2-chloro-ethylphosphonic acid - Fe(III)-EDTA ethylenediaminetetraacetic ferric-sodium salt - IAA indole-acetic acid - TIBA triiodobenzoic acid     

Detecting non-neutral heterogeneity across a region of DNA sequence in the ratio of polymorphism to divergence

Natural selection, in the form of balancing selection or selective sweeps, can result in a decoupling of the amounts of molecular polymorphism and divergence. Thus natural selection can cause some areas of DNA sequence to have greater silent polymorphism, relative to divergence between species, than other areas. It would be useful to have a statistical test for heterogeneity in the polymorphism to divergence ratio across a region of DNA sequence, one that could identify heterogeneity greater than that expected from the neutral processes of mutation, drift, and recombination. The only currently available test requires that a region be arbitrarily divided into sections that are compared with each other, and the subjectivity of this division could be problematic. Here a test is proposed in which runs of polymorphic and fixed sites are counted, where a "run" is a set of one or more sites of one type preceded and followed by the other type. The number of runs is smaller than otherwise expected if polymorphisms are clumped together. By simulating neutral evolution and comparing the observed number of runs to the simulations, a statistical test is possible which does not require any a priori decisions about subdivision.      

High Variation of Fluorescence Protein Maturation Times in Closely Related Escherichia coli Strains

Fluorescent proteins (FPs) are widely used in biochemistry, biology and biophysics. For quantitative analysis of gene expression FPs are often used as marking molecules. Therefore, sufficient knowledge of maturation times and their affecting factors is of high interest. Here, we investigate the maturation process of the FPs GFP and mCherry expressed by the three closely related Escherichia coli strains of the Colicin E2 system, a model system for colicinogenic interaction. One strain, the C strain produces Colicin, a toxin to which the S strain is sensitive, and against which the R strain is resistant. Under the growth conditions used in this study, the S and R strain have similar growth rates, as opposed to the C strain whose growth rate is significantly reduced due to the toxin production. In combination with theoretical modelling we studied the maturation kinetics of the two FPs in these strains and could confirm an exponential and sigmoidal maturation kinetic for GFP and mCherry, respectively. Our subsequent quantitative experimental analysis revealed a high variance in maturation times independent of the strain studied. In addition, we determined strain dependent maturation times and maturation behaviour. Firstly, FPs expressed by the S and R strain mature on similar average time-scales as opposed to FPs expressed by the C strain. Secondly, dependencies of maturation time with growth conditions are most pronounced in the GFP expressing C strain: Doubling the growth rate of this C strain results in an increased maturation time by a factor of 1.4. As maturation times can vary even between closely related strains, our data emphasize the importance of profound knowledge of individual strains'' maturation times for accurate interpretation of gene expression data.     

The Influence of Antimicrobial Peptides and Mucolytics on the Integrity of Biofilms Consisting of Bacteria and Yeasts as Affecting Voice Prosthetic Air Flow Resistances

The integrity of biofilms on voice prostheses used to rehabilitate speech in laryngectomized patients causes unwanted increases in airflow resistance, impeding speech. Biofilm integrity is ensured by extracellular polymeric substances (EPS). This study aimed to determine whether synthetic salivary peptides or mucolytics, including N-acetylcysteine and ascorbic acid, influence the integrity of voice prosthetic biofilms. Biofilms were grown on voice prostheses in an artificial throat model and exposed to synthetic salivary peptides, mucolytics and two different antiseptics (chlorhexidine and Triclosan). Synthetic salivary peptides did not reduce the air flow resistance of voice prostheses after biofilm formation. Although both chlorhexidine and Triclosan reduced microbial numbers on the prostheses, only the Triclosan-containing positive control reduced the air flow resistance. Unlike ascorbic acid, the mucolytic N-acetylcysteine removed most EPS from the biofilms and induced a decrease in air flow resistance.