Functional morphology of Tethya species (Porifera): 2. Three-dimensional morphometrics on spicules and skeleton superstructures of T. minuta

The biomechanics of body contraction in Porifera is almost unknown, although sponge contraction has been observed already in ancient times. Some members of the genus Tethya represent the most contractile poriferan species. All of them show a highly ordered skeleton layout. Based on three main spicule types, functional units are assembled, termed skeleton superstructures here. Using synchrotron radiation based x-ray microtomography and quantitative image analysis with specially developed particle and structure recognition algorithms allowed us to perform spatial allocation and 3D-morphometric characterizations of single spicules and skeleton superstructures in T. minuta. We found and analyzed three skeleton superstructures in the investigated specimen: (1) 85 megasclere bundles, (2) a megaster sphere, composed by 16,646 oxyasters and (3) a pinacoderm–tylaster layer composed by micrasters. All three skeleton superstructures represent composite materials of siliceous spicules and extracellular matrix. From structure recognition we developed an abstracted mathematical model of the bundles and the sphere. In addition, we analyzed the megaster network interrelation topology and found a baso-apical linear symmetry axis for the megaster density inside the sphere. Based on our results, we propose a hypothetical biomechanical contraction model for T. minuta and T. wilhelma, in which the skeleton superstructures restrain physical stress generated by contraction in the tissue. While skeletal structures within the genus Tethya have been explained using R. Buckminster Fullers principle of tensegrity by other authors, we prefer material science based biomechanical approaches, to understand skeletal superstructures by referring to their composite material properties.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Interactions between genes and environmental factors in asthma and atopy: new developments

Asthma and associated phenotypes are complex traits most probably caused by an interaction of multiple disease susceptibility genes and environmental factors. Major achievements have occurred in identifying chromosomal regions and polymorphisms in candidate genes linked to or associated with asthma, atopic dermatitis, IgE levels and response to asthma therapy. The aims of this review are to explain the methodology of genetic studies of multifactorial diseases, to summarize chromosomal regions and polymorphisms in candidate genes linked to or associated with asthma and associated traits, to list genetic alterations that may alter response to asthma therapy, and to outline genetic factors that may render individuals more susceptible to asthma and atopy due to environmental changes.     

Histochemical and biochemical urease localization in the periplasm and outer membrane of two Proteus mirabilis strains

Proteus mirabilis, a gram-negative bacillus, is often implicated in the formation of infectious kidney stones. As ureolytic activity of this organism is thought to play a major role in its pathogenesis, we adapted our recently described urease localization technique to visualize urease activity in vivo. Urease activity was ultrastructurally localized in two clinically isolated P. mirabilis strains by precipitating the enzymatic reaction product (ammonia) with sodium tetraphenylboron. Subsequent silver staining of the cells revealed urease activity to be predominantly associated with the periplasm and outer membranes of each strain. Biochemical measurements of urease activity in P. mirabilis cell fractions correlated well with histochemical observations in that the majority of urease activity was associated with the periplasm. Membrane-bound urease activity of these strains was associated mainly with the peptidoglycan in the detergent-insoluble (outer membrane) fraction.     

Tardigrades of South America: Machu Picchu and Ollantaytambo, Peru

During July 1999, a study group from the University of Kansas visited the ancient Inca ruins in and around Machu Picchu and Ollantaytambo, Peru. They collected lichens and mosses from the rock walls around the ruins. The samples contained four genera and six species of tardigrades. No associational patterns and relationships were detected. A new species, Echiniscus ollantaytamboensis nov. sp. is described.     

l-Proline transport into renal OK epithelial cells: a second renal proline transport system is induced by amino acid deprivation

Influx of [³H]-l-proline into renal OK cells revealed that basal transport was mediated by the transporter SIT1. When cells were submitted for 8 h to amino acid deprivation, uptake of l-proline was now dominated by a low-affinity system with an apparent K _m of 4.4 ± 0.6 mM and a V _max of 10.2 ± 0.6 nmol/mg of protein/min operating in addition to the high-affinity SIT1 system with a K _m of 0.12 ± 0.01 mM and a V _max of 0.28 ± 0.04 nmol/mg of protein/min. The low- and high-affinity proline transporting systems were sensitive to inhibitors of JNK and PI-3 kinases, whereas a GSK-3 inhibitor affected only the upregulated transport system. Ion-replacement studies and experiments assessing substrate specificities for both systems provided strong evidence that SNAT2, that showed two- to threefold increased mRNA levels, is the responsible transporter mediating the increased proline influx under conditions of amino acid deprivation.     

Methylation of the mouse M-lysozyme downstream enhancer inhibits heterotetrameric GABP binding.

Expression of the mouse M-lysozyme gene is a specific marker for the differentiation of macrophage/granulocyte cell lineages. Analysis of the mechanisms regulating M-lysozyme gene expression revealed an enhancer element in the 3'-flanking region of the gene, termed the M-lysozyme downstream enhancer (MLDE). Here we demonstrate that the nuclear factors binding to MLDE are present in all tested myeloid and non-myeloid mouse cell lines. Sequence analysis of MLDE identified two different sequences, CAGGAAGT and CCGGAAGT, which match the consensus binding sequences for proteins of the ets gene superfamily. The two sites are oriented palindromicly and separated by 10 bp. DMS/DEPC interference assays revealed different patterns of DNA-protein contacts on the two sites. Mutation of each consensus sequence leads to an individual change in protein binding in vitro. Despite these differences, both sequences are bound by GABP, forming a heterotetrameric complex. Tissue specificity is correlated with demethylation of a single CpG dinucleotide located in one of the two Ets motifs. This site when methylated inhibits GABP binding to both sequences in non-macrophage cell types.