Nanoscale structure of type I collagen fibrils: Quantitative measurement of D-spacing

This article details a quantitative method to measure the D-periodic spacing of type I collagen fibrils using atomic force microscopy coupled with analysis using a two-dimensional fast fourier transform approach. Instrument calibration, data sampling and data analysis are discussed and comparisons of the data to the complementary methods of electron microscopy and X-ray scattering are made. Examples of the application of this new approach to the analysis of type I collagen morphology in disease models of estrogen depletion and osteogenesis imperfecta (OI) are provided. We demonstrate that it is the D-spacing distribution, not the D-spacing mean, that showed statistically significant differences in estrogen depletion associated with early stage osteoporosis and OI. The ability to quantitatively characterize nanoscale morphological features of type I collagen fibrils will provide important structural information regarding type I collagen in many research areas, including tissue aging and disease, tissue engineering, and gene knockout studies. Furthermore, we also envision potential clinical applications including evaluation of tissue collagen integrity under the impact of diseases or drug treatments.     

Enzyme-linked immunosorbent assay of antigens from Candida albicans circulating in infected mice and rabbits: The role of mannan

Various antisera raised either to antigens ofCandida albicans or to sub-lethal infections of blastospores (convalescent sera) were tested for their efficacy in diagnosing systemic disease in artifically infected animals. Globulin from convalescent serum, when conjugated with alkaline phosphatase and used in enzyme-linked immunosorbent assays (ELISA), was the only antiserum type which detected circulatingCandida-related antigen in the serum of infected animals. Conjugates made from anti-mannan, anti-blastospore or antimycelial globulin did not detect antigen. Mannan did not appear to be related to an antigen produced in sera of experimentally infected mice. The significance of these results in the diagnosis of systemic candidosis is discussed.     

Knowledge-based models for predicting species occurrence in arable conditions

This paper explores the potential of rule-based habitat models to predict the occurrence of some common species in arable conditions. Models were developed for 10 arable plant species, 7 Hemiptera species, 8 carabid species and for 5 bird species whose ecology was sufficiently known. Rule sets linking species occurrence to environmental variables were produced using available literature and expert knowledge about ecological requirements of the selected species. Environmental variables described the nature and condition of habitats at various scales, ranging from vegetation quadrat to the landscape in a 1 km radius of species sampling sites. The performance of the 34 models developed was assessed in two areas of England. Results show the rule-based habitat models developed for arable plants and birds were not very successful with Cohen's k values often <0.4 for plants and very close to 0 for all bird species. Conversely, rule-based models performed surprisingly well for carabids and Hemiptera with k values on average >0.4. This suggests that ecological knowledge on these invertebrate species is more complete than we expected. The effect of species prevalence on model performance and the potential application of knowledge-based habitat models in the context of biodiversity assessment are discussed.     

Developmental Changes in the Visual Pigments of the Yellowfin Tuna, Thunnus Albacares

Previous studies have suggested that adult tunas have only two visual pigments in their retinas - a rod pigment with a wavelength at maximum absorbance ( λmax ) around 485 nm and one with similar λmax in both twin and single cones inferred from extraction data. Using microspectrophotometry we confirm the presence of a λmax 483 nm visual pigment in the rods of adult yellowfin tuna and a λmax 485 nm pigment in both members of the twin cones. However, all single cones contain a previously undetected violet visual pigment with λmax 426 nm making the adult yellowfin tuna a photopic dichromat. The situation for larvae and early juveniles is different from that of the adults. The all single-cone retina of preflexion larvae shows a wide distribution in individual cone absorbances suggesting not only mixtures of the two adult cone pigments, but the presence of at least a third visual pigment with λmax greater than 560 nm. With growth, the variation in cone absorbances decreases with convergence to the adult condition coincident with cone twinning. The significance of λmax variability, multiple visual pigment expression and age-related differences are discussed in terms of the visual ecology of larval, juvenile and adult tunas.