Kinetics of reaction zone formation with radial diffusion of ligands over a receptor-coated surface

Theoretical calculations are presented, describing the kinetics of reaction zone formation with radial diffusion of ligands over a receptor coated surface. Calculated concentration distributions of ligands diffusing radially over a receptor-coated surface are combined with different types of receptor-ligand reactions, taking place at the surface, in order to obtain theoretical relations between the initial concentration of ligand in the source, the diameter of the receptor-ligand reaction zone and reaction time. These relations are compared to experimental data, using bovine serum albumin (BSA) as immobilized receptor and anti-BSA antibodies as diffusing ligand. The theory predicts how the diffusion constant of the ligand and the detection level of the visualization method may be determined and how to discriminate between different kinetics of the receptor-ligand reaction. The practical use of the theory in experimental studies of receptor-ligand interaction is discussed.     

Glutaminyl-peptide gamma-glutamyltransferase dependence of the uptake of trypsin-alpha-macroglobulin complexes by macrophages

The canine alpha-macroglobulin 125I-trypsin complexes were prepared and exposed to canine alveolar macrophages. The binding of the complexes to cells was time- and dose-dependent. A rapid uptake and degradation of the bound complexes was evidenced by the finding of less than 20% cell-bound radioactivity after a 4 h incubation at 20 degrees C. The canine alveolar macrophages contain a glutaminyl-peptide gamma-glutamyltransferase which shows slightly retarded agarose gel electrophoretic mobility as compared to the respective enzymes from tissues of other species, such as guinea pig and man. Evidence is presented that the binding and degradation of trypsin alpha-macroglobulin complexes by macrophages is dependent on this gamma-glutamyltransferase. Monodansylthiacadaverine, a strong inhibitor of this enzyme, blocks the binding of trypsin-alpha-macroglobulin complexes to macrophages and (probably as a consequence of this) degradation of the complexes. Furthermore, this gamma-glutamyltransferase is a calcium-dependent enzyme and the process of binding trypsin-alpha-macroglobulin complexes to the macrophages was likewise found to be calcium-dependent.     

The metabolism of 4-androstene-3,17-dione by isolated rat hepatocytes. Maintenance of the sex differences in culture

Hepatocytes from adult rats were isolated and cultivated as primary monolayers for 3 days in a medium containing only 1% homologous serum. The metabolism of 4-androstene-3,17-dione was followed in hepatocytes from male, female and hypophysectomized animals. It was found that immediately after preparation, 5alpha-reductase and 16alpha-hydroxylase activities were present in the cells in amounts comparable to those found in microsomal preparations from liver homogenates. After 3 days in culture, these enzyme activities had decreased to about half the values measured on day 0. During this time the sexual differences in steroid metabolism in the cells were stable, i.e. there was no detectable induction of 16alpha-hydroxylase in cells from female animals, and the relative sex difference in 5alpha-reductase activity persisted.     

Transamidating enzymes in maternal plasma and placenta in human pregnancies complicated by intrauterine growth retardation

Transamidases are enzymes, which are necessary for normal clot formation. They fall into two types: thrombin-dependent Factor XIII and thrombin-independent tissue transglutaminases. The investigation showed that human placenta contains not only Factor XIII, but also considerable amounts of a tissue trans-glutaminase identical with an enzyme present in red blood cells. A quantitative assay for transamidases, using incorporation of radioactively labelled putrescine into casein, was applied to placental extracts. With this assay the amounts of thrombin-dependent and thrombin-independent transamidases were determined in the placenta of fullterm infants and term infants who were small for gestational age. The transamidase activities of the placenta in the two groups showed no statistically significant difference. Plasma Factor XIII subunit a antigen concentration was increased by about 40% in midpregnancy and returned to normal nonpregnant values in the 3rd trimester, but when intrauterine growth was retarded the plasma Factor XIII concentration remained elevated. Plasma Factor XIII activities showed a similar variation.     

Disentangling genetic and epigenetic determinants of ultrafast adaptation

A major rationale for the advocacy of epigenetically mediated adaptive responses is that they facilitate faster adaptation to environmental challenges. This motivated us to develop a theoretical–experimental framework for disclosing the presence of such adaptation‐speeding mechanisms in an experimental evolution setting circumventing the need for pursuing costly mutation–accumulation experiments. To this end, we exposed clonal populations of budding yeast to a whole range of stressors. By growth phenotyping, we found that almost complete adaptation to arsenic emerged after a few mitotic cell divisions without involving any phenotypic plasticity. Causative mutations were identified by deep sequencing of the arsenic‐adapted populations and reconstructed for validation. Mutation effects on growth phenotypes, and the associated mutational target sizes were quantified and embedded in data‐driven individual‐based evolutionary population models. We found that the experimentally observed homogeneity of adaptation speed and heterogeneity of molecular solutions could only be accounted for if the mutation rate had been near estimates of the basal mutation rate. The ultrafast adaptation could be fully explained by extensive positive pleiotropy such that all beneficial mutations dramatically enhanced multiple fitness components in concert. As our approach can be exploited across a range of model organisms exposed to a variety of environmental challenges, it may be used for determining the importance of epigenetic adaptation‐speeding mechanisms in general.     

Ovine reference materials and assays for prion genetic testing

Background  

Genetic predisposition to scrapie in sheep is associated with several variations in the peptide sequence of the prion protein gene (PRNP). DNA-based tests for scoring PRNP codons are essential tools for eradicating scrapie and for evaluating rare alleles for increased resistance to disease. In addition to those associated with scrapie, there are dozens more PRNP polymorphisms that may occur in various flocks. If not accounted for, these sites may cause base-pair mismatching with oligonucleotides used in DNA testing. Thus, the fidelity of scrapie genetic testing is enhanced by knowing the position and frequency of PRNP polymorphisms in targeted flocks.     

Multimodal signals in male European treefrog (Hyla arborea) and the influence of population isolation on signal expression

In nocturnal treefrogs, mate choice implies the use of acoustic and visual signals. Multimodality is suspected to have evolved for either information redundancy or information complementariness. It is essential to explore multimodality in a natural context to understand the selection pressures operating on the signals. In the present study, we investigated calling and coloration in relation to male biometry and condition in four populations of European treefrog (Hyla arborea) varying in size and genetic isolation. We compared the signal intensity between core and satellite populations to estimate the impact of genetic diversity on male secondary sexual traits. The results obtained show important regional variations in both traits, likely as a result of local adaptations. Call and coloration are weakly correlated within an individual, implying that these traits likely convey different information about the signaller's identity or quality, thus supporting the hypothesis of complementariness of multiple messages. By contrast to the experimental evidence, we find that call and coloration are not related to male condition (as estimated by the residual of mass over size), suggesting that the condition‐dependence of these traits may be mediated by complex mechanisms not accurately reflected by the chosen estimator. Finally, male call and colour phenotypes present no robust pattern of variation with isolation status, probably because of variation in local selective pressures and in history of population dynamics. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 633–647.     

Analyzing genes using closing and replicating circles

During the past two years, significant breakthroughs have been achieved in genetic analyses through the application of technologies based on analytical DNA-circularization reactions. Padlock probes and molecular inversion probes have enabled parallel, high-throughput single nucleotide polymorphism (SNP) genotyping at increased scales, whereas, at the other end of the analysis spectrum, DNA molecules in individual cells have been genotyped, in situ, using padlock probes and rolling-circle amplification (RCA). This review describes the recent developments in the technologies that use specific DNA circularization, coupled to DNA amplification through PCR or rolling-circle amplification, and addresses the great potential of these tools.     

Patch use behaviour in benthic fish depends on their long-term growth prospects

Animals foraging in a heterogeneous environment may combine prior information on patch qualities and patch sample information to maximize intake rate. Prior information dictates the long-term expectations, whereas prior information in combination with patch sample information determines when to leave an individual food patch. We examined patch use behaviour of benthic feeding fish in their natural environment at different spatial scales to test if they could determine patch quality and if patch use behaviour was correlated with environmental quality. In seven lakes along a gradient of environmental quality (measured as maximum benthivore size), we made repeated measurements of giving-up density (GUD) in artificial food patches of different qualities. At the largest spatial scale, between lakes, we tested if giving-up densities revealed the long-term growth expectation of benthic fish. At the local scale of patches and micro patches we tested for the ability of benthic fish to assess patch quality, and how this ability depended on the patch exploitation levels between the different lakes. We found that GUD was positively related to maximum size of bream, suggesting that short-term behavioural decisions reflected long-term growth expectations. Benthic fish discriminated between nearby rich and poor patches, but not between rich and poor micropatches within a food patch. This suggests that the foraging scale of benthic fish lies between the patch and micro patch scale in our experiments. We conclude that patch use behaviour of benthic fish can provide a powerful measure of habitat quality that reveals how benthic fish perceive their environment.