Functional dissimilarity of melanomacrophage centres in the liver and spleen from females of the teleost fish <Emphasis Type="Italic">Prochilodus argenteus</Emphasis>

Melanomacrophage centres (MMCs) are formed by macrophage aggregates containing pigments such as hemosiderin, melanin and lipofuscin. MMCs are found in animals such as reptiles, amphibians and, mainly, fishes, in organs such as the kidney, spleen, thymus and liver. In teleost fish, several functions have been attributed to MMCs, including the capture and storage of cations, the phagocytosis of cellular debris and immunological reactions. As the use of MMCs has been suggested as a tool for the assessment of environmental impacts, our aim has been to describe the various metabolic processes performed by MMCs in diverse organs (liver and spleen) by using the teleost Prochilodus argenteus as an animal model. MMCs from the liver and spleen were assessed by histochemistry, transmission electron microscopy, scanning electron microscopy, X-ray microanalysis techniques and biochemical assay for N-acetylglucosaminidase activity. The data showed metabolic differences in MMCs between the liver and spleen of P. argenteus in their morphometric characteristics and biochemical and elemental composition. The implications of these findings are discussed, focusing on their role in organ metabolism.     

Tubulin potentiates the interaction of the metalloendopeptidase nardilysin with the neuronal scaffold protein p42<Superscript>IP4</Superscript>/centaurin-α1 (ADAP1)

We found colocalization of the neuronal protein p42^IP4 (centaurin-α1; ArfGAP with dual pleckstrin homology domain [ADAP1]), the metalloendopeptidase nardilysin (NRD; involved in axonal maturation and myelination) and tubulin in the cytosol and at the plasma membrane of SH-SY5Y neuroblastoma cells. To examine the importance of tubulin for the interaction of NRD with p42^IP4, we treated cells with nocodazole, which interferes with tubulin polymerization. Nocodazole did not affect the colocalization of p42^IP4 and tubulin but caused a clear redistribution of the proteins in cells, so that the colocalization of p42^IP4, tubulin and NRD was visible exclusively in multiple foci. To reveal the mechanism of the interaction between NRD, p42^IP4 and tubulin observed in neuronal cells, we performed Far-Western blotting, a technique that directly detects protein-protein interactions on Western blots. This technique demonstrated that tubulin enhanced the binding of NRD to functionally renatured p42^IP4. The mutation of a highly conserved cysteine residue in NRD to alanine abolished the potentiation by tubulin. NRD lacking the characteristic acidic domain was able to bind p42^IP4 but addition of tubulin did not significantly potentiate the binding of this deletion mutant to p42^IP4. A function-abolishing mutation of the Zn²⁺-binding motif of NRD did not affect the potentiation by tubulin. Thus, the capacity of tubulin to enhance the interaction between p42^IP4 and NRD together with the known interaction of p42^IP4 with F-actin support the novel notion that p42^IP4 plays a possible role as a linker between the two networks, actin and tubulin, in neural cells.     

Ecto-5′-nucleotidase/CD73 knockdown increases cell migration and mRNA level of collagen I in a hepatic stellate cell line

Ecto-5′-nucleotidase (eNT/CD73, E.C.3.1.3.5) is a glycosyl phosphatidylinositol (GPI)-linked cell-surface protein with several functions, including the local generation of adenosine from AMP, with the consequent activation of adenosine receptors and the salvaging of extracellular nucleotides. It also apparently functions independently of this activity, e.g., in the mediation of cell-cell adhesion. Liver fibrosis can be considered as a dynamic and integrated cellular response to chronic liver injury and the activation of hepatic stellate cells (HSCs) plays a role in the fibrogenic process. eNT/CD73 and adenosine are reported to play an important role in hepatic fibrosis in murine models. Knockdown of eNT/CD73 leads to an increase in mRNA expression of tissue non-specific alkaline phosphatase (TNALP), another AMP-degrading enzyme and thus no alteration is seen in the total ecto-AMPase activity of the cell. eNT/CD73 knockdown also leads to changes in the expression of collagen I and a clear alteration of cell migration. We suggest that eNT/CD73 protein expression controls cell migration and collagen expression in a mechanism independent of changes in nucleotide metabolism.     

Evolution of immune-neuroendocrine integration from an ecological immunology perspective

Bow tie architecture can support evolutionary integration between the immune and neuroendocrine systems, answering ecological immunology demands in terms of economy and efficiency.     

Ammonium and attachment of <Emphasis Type="Italic">Rhodopirellula baltica</Emphasis>

A dimorphic life cycle has been described for the planctomycete Rhodopirellula baltica SH1^T, with juvenile motile, free-swimming cells and adult sessile, attached-living cells. However, attachment as a response to environmental factors was not investigated. We studied the response of R. baltica to nitrogen limitation. In batch cultures, ammonium limitation coincided with a dominance of free-swimming cells and a low number of aggregates. Flow cytometry revealed a quantitative shift with increasing ammonium availability, from single cells towards attached cells in large aggregates. During growth of R. baltica on glucose and ammonium in chemostats, an ammonium addition caused a macroscopic change of the growth behaviour, from homogeneous growth in the liquid phase to a biofilm on the borosilicate glass wall of the chemostat vessel. Thus, an ammonium limitation—a carbon to nitrogen supply ratio of 30:1—sustained free-living growth without aggregate formation. A sudden increase in ammonium supply induced sessile growth of R. baltica. These observations reveal a response of Rhodopirellula baltica cells to ammonium: they abandon the free-swimming life, attach to particles and form biofilms.     

Phylogeny and compatibility: plasmid classification in the genomics era

Whole genome sequences are present-day bonanzas for taxonomists. Comparative genomics provides a promising perspective to reveal the evolutionary relationship between organisms, but this strategy is not applicable for extrachromosomal elements due to their high recombination frequencies. Classification of plasmids is based on their compatibility, i.e., the ability to coexist within the same cell. Compatibility testing is a laborious experimental discipline of pairwise comparisons developed for a small set of replicons. Thus, novel approaches are urgently required to deal with the exponentially increasing amount of sequence data. In this minireview, a short overview about the functional role and distribution of plasmids as well as a summary of recent strategies to classify the replicons via phylogenetic analyses is given. Our own work essentially bases on genes of the replication module, i.e., the replicase and two conserved partitioning genes and we exemplified this approach for the four different plasmid types from Alphaproteobacteria. It is suitable for a reliable classification of these replicons and allows in silico predictions about their compatibility. The development of a general classification scheme for plasmids from all microbial lineages will ensure a systematic assessment of the upcoming data flood and help to understand the distribution of extrachromosomal elements.     

The variability of male quality and female mate choice decisions: second-order stochastic dominance and the behavior of searchers under a sequential search strategy

The strategy employed by a female to sample prospective mates determines the likelihood that a high-quality male is encountered in the search process. In general, the choosiness of females is expected to depend on the variability of quality amongst the males that are sampled. The sequential search strategy is a prominent model of search behavior that involves the use of a threshold criterion to evaluate encountered individuals. In this paper, we show that the stochastic dominance of one distribution of male quality over another at the second order is necessary and sufficient for the optimal threshold criterion to differ under two distributions of male quality when the cost to sample males is held constant and the mean quality of males under each of the distributions is identical. A difference of the variance of male quality between two distributions does not imply that one distribution stochastically dominates the other at the second order and, hence, should not, in general, be used to assess the relative variability of quality amongst prospective mates. The adjustment of the threshold criterion in response to experimental manipulations of the distribution of male quality has been inferred from induced differences of the duration of search or the number of males sampled in the search process. Here we show that such inferences are unjustified. In particular, the difference of the threshold criterion imposed by second-order stochastic dominance does not determine the distribution under which females are expected to sample a larger number of males in the search process.     

Sustained oscillations for density dependent Markov processes

Simulations of models of epidemics, biochemical systems, and other bio-systems show that when deterministic models yield damped oscillations, stochastic counterparts show sustained oscillations at an amplitude well above the expected noise level. A characterization of damped oscillations in terms of the local linear structure of the associated dynamics is well known, but in general there remains the problem of identifying the stochastic process which is observed in stochastic simulations. Here we show that in a general limiting sense the stochastic path describes a circular motion modulated by a slowly varying Ornstein–Uhlenbeck process. Numerical examples are shown for the Volterra predator–prey model, Sel’kov’s model for glycolysis, and a damped linear oscillator.     

A stability analysis of the power-law steady state of marine size spectra

This paper investigates the stability of the power-law steady state often observed in marine ecosystems. Three dynamical systems are considered, describing the abundance of organisms as a function of body mass and time: a “jump-growth” equation, a first order approximation which is the widely used McKendrick–von Foerster equation, and a second order approximation which is the McKendrick–von Foerster equation with a diffusion term. All of these yield a power-law steady state. We derive, for the first time, the eigenvalue spectrum for the linearised evolution operator, under certain constraints on the parameters. This provides new knowledge of the stability properties of the power-law steady state. It is shown analytically that the steady state of the McKendrick–von Foerster equation without the diffusion term is always unstable. Furthermore, numerical plots show that eigenvalue spectra of the McKendrick–von Foerster equation with diffusion give a good approximation to those of the jump-growth equation. The steady state is more likely to be stable with a low preferred predator:prey mass ratio, a large diet breadth and a high feeding efficiency. The effects of demographic stochasticity are also investigated and it is concluded that these are likely to be small in real systems.