Fluid–structure interaction modeling of compliant aortic valves using the lattice Boltzmann CFD and FEM methods

Biomechanics and Modeling in Mechanobiology - The lattice Boltzmann method (LBM) has been increasingly used as a stand-alone CFD solver in various biomechanical applications. This study proposes a...     

Depolarization-independent net uptake of calcium into clonal insulin-releasing cells exposed to glucose

Insulin release, net fluxes of Ca²⁺, and glucose metabolism were studied in a clonal cell line (RINmSF) established from a transplantable rat islet tumor. The insulin content amounted to only 0.03% of that of the total protein and decreased even further with subsequent passages. The insulin secretion was as high as 10 to 20% of the total hormone content per hour. Insulin release was stimulated by K⁺ depolarization but not by exposure to glucose. In contrast to this secretory pattern, glucose but not K⁺ stimulated the net uptake of Ca²⁺ at micromolar concentrations of the ion. The glucose effect was not mimicked by 20 mM 3-O-methylglucose. It was as pronounced at 1 mM as at 20 mM of the sugar and corresponded to an uptake of 119 fmol cm^–2 s^–1. Glucose metabolism was typical for tumor cells with a high glycolytic flux and an oxidationtoutilization ratio as low as 0.05–0.15. Maximal oxidative degradation was attained already at l mM. This concentration was also equivalent to the K_m for glucose utilization, indicating a substantial left-hand shift of the normal dose-response curve. It is suggested that glucose induces a depolarizationindependent net uptake of Ca²⁺ by favouring intracellular buffering of the cation.     

Bruterfolg, Siedlungsdichte und Raumnutzung der Elster (Pica pica) in unterschiedlichen Habitaten

Zusammenfassung Auf einer Fläche von 128 km² im Raum Rayreuth (Oberfranken) wurde der Einfluß verschiedener Faktoren auf Bruterfolg, Nestbau, Siedlungsdichte und Nistplatzwahl der Elster durch multivariable statistische Methoden geprüft. Größte Bedeutung kam der Lage zur Siedlung zu: Elstern innerhalb von Siedlungen hatten einen vergleichsweise höheren Bruterfolg und eine höhere Siedlungsdichte. Das Habitat (Stadt, Stadtrand, Land) spielte demgegenüber eine geringere Rolle. Ein Einfluß potentieller Feinde (Rabenkrähe, Habicht) war (vermutlich wegen zu geringer Dichte) nicht erkennbar. Die mögliche Beziehung zur Wacholderdrossel wird als gemeinsame Nutzung von Grünland als wichtigste Nahrungsquelle diskutiert. Waldrandnahe Standorte wurden gemieden. Die Höhenlage hatte nur einen geringen Einfluß auf Bruterfolg und Nestbauverhalten. Von verschiedenen das Nest betreffenden Parametern (Baumtyp, Baumhöhe, Exposition, Blattaustrieb, Nestausbau, Nestalter) hatte nur das Nestalter einen deutlichen positiven Effekt auf den Bruterfolg. Bei der Wahl eines Nistplatzes war die Baumhöhe die einzig erkennbare wichtige Größe: Elstern nutzten höhere Bäume als dem durchschnittlichen Angebot entsprach. Die Bedeutung anderer Faktoren (Nistplatzangebot, Jagd) und die Beziehung zwischen den verschiedenen Parametern wird diskutiert.

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Breeding success, density and dispersion of the Magpie (Pica pica) in different habitats

Summary The influence of several factors on breeding success, nesting behaviour, density and selection of nesting sites was investigated on a study plot of 128 km² in northeastern Bavaria (Bayreuth, Oberfranken). The position to human settlement is the most important factor: Magpies within settlements showed a higher breeding success and density than outside (Tab. 5); the habitat (rural, urban, outskirts) was less important. Potential predators (GoshawkAccipiter gentilis, Carrion CrowCorvus corone corone) had no effect, Probably because of its low densities. The relation to colonies of the Fieldfare (Turdus pilaris) is interpreted as a common use of grassland as feeding site during the breeding season (Tab. 5). Magpies seem to avoid the vicinity of forests (Tab. 4). The altitude had only a slight effect on breeding success and nesting behaviour. Among several factors which refer to the nesting site (tree type, height, exposition, period of leaf break, nest type) only the nest age had a clear (positive) effect on breeding success. Magpies preferred higher trees for nest-building (Tab. 4). The influence of other factors (density of nest sites, hunting, character of trees) and the relation between the different factors are discussed.

     

In vitro anamnestic immune responses and modulating factors

Summary The term anamnestic refers to the specific and enhanced immune responses of antigen-immunized (primed) lymphoid memory cells to secondary challenge with a foreign substance (antigen). These responses include the accelerated and quantitatively greater syntheses of antibody and other macromolecules than upon primary challenge of such cells. Rabbits were primarily immunized with keyhole limpet hemocyanin (KLH). Six days later their memory lymph node cells (LNC) were removed, and upon culture with KLH, responded with the synthesis of antibody, immunoglobulin (Ig), protein, DNA and RNA, as well as with active transport of dibutryl cyclic AMP (DbcAMP). Purified thymus-derived (T) LNC were prepared on anti-rabbit Ig affinity columns. Bursal-equivalent (B) cells were prepared by binding to a complex of sheep erythrocytes (SRBC)-antibody to SRBC-complement and centrifugation of these complexes on suitable gradients. When these T and B KLH-primed LNC were mixed and challenged with KLH the aforementioned macromolecular syntheses and active transport occurred. Indeed, by a variety of criteria, the reconstituted anamnestic immune responses were indistinguishable from these responses of unfractionated LNC. Antigenic stimulation of KLH-primed T cells induced the synthesis of proteins and DNA, but not antibody, but antigenic challenge of KLH-primed B cells did not evoke these syntheses. However, added KLH induced a mixture of T and B antigen-primed LNC to synthesize more protein, Ig, DNA than either population alone and more antibody than T cells per se; B cells required help for all of these responses. The thymus (T) cell-dependent phase of in vitro anamnestic antibody response lasted the first 24–36 hr.The antibody response was regulated by antigen-concentration. One g KLH evoked maximal antibody synthesis, 10 and 100 g KLH much less. Challenge of the separated T and B cell populations with different KLH concentrations, followed by recombination and eventual assay of antibody synthesis revealed different optima. The optimal concentration for T cell help was 0.01–0.1 g KLH; higher amounts induced much less antibody production. The optimum for B cells was 1–10 g KLH; 100 g inhibited antibody formation.The antibody response to KLH and human serum albumin (HSA) was regulated nonspecifically utilizing LNC from rabbits immunized simultaneously with these two antigens. Thus stimulation of LNC from these rabbits with either antigen induced the synthesis of antibodies to both antigens. HSA and KLH did not cross-react either serologically or cellularly. Cross-stimulation of antibody synthesis also was observed when rabbit LNC were primed with KLH and Mb. However, in this instance, cross-reaction between KLH and sperm-whale myoglobulin (Mb) was observed at the cellular, presumably the T cell, level, although not at the antibody (B cell) level. The antibody response could also be modulated by exogenous cholera enterotoxin (CT), dibutyryl cyclic AMP (DbcAMP) and prostaglandins of the E series. The addition of each substance together with 1–100 g KLH to KLH-primed LNC enhanced the antibody response many-fold. CT-induced non-immunized LNC to produce soluble factor(s) (SF) which, when added to KLH-primed LNC together with KLH, enhanced antibody synthesis significantly. The addition of Indomethacin, an inhibitor of PGE synthesis to KLH-immunized cells together with KLH inhibited antibody production, suggesting that PGE was involved in this response. Evidence was adduced that neither cyclic AMP nor PGE was required for the antibody response: Ca²⁺ was not required for induction of this response by KLH, but only its regulation by cAMP.Moreover, when KLH-primed LNC were fractionated on Nylon columns, the effluent cells were induced by KLH to synthesize antibody, but this synthesis was not enhanced by added DbcAMP or PGE; presumably, regulatory cells were removed on the column. Added KLH induced PGE synthsis in these cultures; this synthesis required macrophages. In all of the LNC cultures — including cultures from rabbits immunized with KLH, HSA, and MB months or a year earlier — much antibody synthesis occurred even when antigen was not added to the cultures. This spontaneous antibody was anamnestic, thymus (T cell)-dependent and involved the interaction of residual immunogen on dendritic cells with T and B memory cells. This spontaneous antibody response provides a model for the study of the factors involved in the longterm maintenance of humoral immunity.Mb was employed as a source of more refined antigenic determinants. Rabbits were immunized with Mb in complete Freunds adjuvant. The addition of small synthetic peptides corresponding to the five antigenic sites of Mb to the Mb-primed LNC induced the synthesis of antibody, Ig, protein, DNA, RNA, and macrophage migration inhibitory factor (MIF). The N terminal 1–6 peptide, which is not antigenic, i.e. does not combine with antibody to Mb, also induced all of these syntheses, except MIF. These peptide-induced responses appeared to be thymus-dependent.Abbreviations AP alum-precipitated - AFab goat IgG antibody to rabbit Fab - ATG goat IgG antibody to rabbit thymocytes - BGG bovine gamma globulin - Bsa bovine serum albumin - BAC bromo acetyl cellulose - B bursalequivalent lymphocytes - CT cholera enterotoxin - CRL complement receptor lymphocytes - DFA complete Freund's adjuvant-, - cAMP adenosine 3:5-cyclic monophosphate - cGMP guanosine 3:5-cyclic monophosphate - DbcAMP N⁶,O²-dibutryl cyclic AMP - EAC sheep erythrocytes sensitized with antibody and complement - FITC fluorescein isothiocyanate - HSA human serum albumin - KLH keyhole limpet hemocyanin - LNC lymph node cells - MEM minimum essectial Eagle's medium - medium; MIF m crophage migration inhibitory factor - Mb sperm-whale myoglobin - PHA phytohemagglutinin - PGE prostaglandins of the E series - PGF prostaglandins of the F series - PGSI inhibitors of prostaglandin systhesis - Slg surface immunoglobulin - T thymus-derived lymphocytes     

Two types of FtsH protease subunits are required for chloroplast biogenesis and Photosystem II repair in Arabidopsis

FtsH protease is important in chloroplast biogenesis and thylakoid maintenance. Although bacteria contain only one essential FTSH gene, multiple genes exist in cyanobacteria and higher plants. However, the functional significance of FTSH multiplication in plants is unclear. We hypothesized that some FTSH genes may be redundant. To test this hypothesis, we generated double mutant combinations among the different FTSH genes in Arabidopsis thaliana. A double mutant of ftsh1 and ftsh8 showed no obvious phenotypic alterations, and disruption of either FTSH1 or FTSH5 enhanced the phenotype of the ftsh2 mutant. Unexpectedly, new phenotypes were recovered from crosses between ftsh2 and ftsh8 and between ftsh5 and ftsh1, including albinism, heterotrophy, disruption of flowering, and severely reduced male fertility. These results suggest that the duplicated genes, FTSH1 and FTSH5 (subunit type A) and FTSH2 and FTSH8 (subunit type B), are redundant. Furthermore, they reveal that the presence of two types of subunits is essential for complex formation, photosystem II repair, and chloroplast biogenesis.     

Selecton: a server for detecting evolutionary forces at a single amino-acid site

SUMMARY: We present an algorithmic tool for the identification of biologically significant amino acids in proteins of known three dimensional structure. We estimate the degree of purifying selection and positive Darwinian selection at each site and project these estimates onto the molecular surface of the protein. Thus, patches of functional residues (undergoing either positive or purifying selection), which may be discontinuous in the linear sequence, are revealed. We test for the statistical significance of the site-specific scores in order to obtain reliable and valid estimates. AVAILABILITY: The Selecton web server is available at: http://selecton.bioinfo.tau.ac.il SUPPLEMENTARY INFORMATION: More information is available at http://selecton.bioinfo.tau.ac.il/overview.html. A set of examples is available at http://selecton.bioinfo.tau.ac.il/gallery.html.     

Identification of methylated sequences in genomic DNA of adult Drosophila melanogaster

The genome of Drosophila melanogaster contains methylated cytosines. Recent studies indicate that DNA methylation in the fruit fly depends on one DNA methyltransferase, dDNMT2. No obvious phenotype is associated with the downregulation of this DNA methyltransferase. Thus, identifying the target sequences methylated by dDNMT2 may constitute the first step towards understanding the biological functions of this enzyme. We used anti-5-methylcytosine antibodies as affinity column to identify the methylated sequences in the genome of adult flies. Our analysis demonstrates that components of retrotransposons and repetitive DNA sequences are putative substrates for dDNMT2. The methylation status of DNA encoding Gag, a protein involved in delivering the transposition template to its DNA target, was confirmed by sodium bisulfite sequencing.     

Death-associated protein 3 localizes to the mitochondria and is involved in the process of mitochondrial fragmentation during cell death

Death-associated protein 3 (DAP3) was previously isolated in our laboratory as a positive mediator of cell death. It is a 46-kDa protein containing a GTP binding domain that was shown to be essential for the induction of cell death. DAP3 functions downstream of the receptor signaling complex, and its death-promoting effects depend on caspase activity. Recent reports have suggested that DAP3 is localized to the mitochondria, but no functional significance of this localization has been reported so far. Here, we study the sub-cellular localization and cellular function of human DAP3 (hDAP3). We found that hDAP3 is localized to the mitochondria and, in contrast to cytochrome c, is not released to the cytoplasm following several cell death signals. Overexpression of hDAP3 induced dramatic changes in the mitochondrial structure involving increased fragmentation of the mitochondria. Both the mitochondrial localization of hDAP3 and its GTP-binding activity were essential for the fragmentation. The punctiform mitochondrial morphology was similar to that observed upon treatment of HeLa cells with staurosporine. In fact, reduction of endogenous hDAP3 protein by RNA interference partially attenuated staurosporine-induced mitochondrial fission. Thus, hDAP3 is a necessary component in the molecular pathway that culminates in fragmented mitochondria, probably reflecting its involvement in the fission process. These results, for the first time, provide a specific functional role for hDAP3 in mitochondrial maintenance.     

Spatial and temporal dynamics of potato tuberworm (Lepidoptera: Gelechiidae) infestation in field-stored potatoes

The potato tuberworm, Phthorimaea operculella (Zeller), is a major pest of potatoes in fields and traditional storage. A common method of nonrefrigerated storage is to pile potatoes in straw-covered heaps in the field. Tubers may be stored up to 3-4 mo in this manner, until the next harvest. We studied the dynamics of potato tuber moth infestation associated with such field storage in a 12-wk experiment in Israel. We set up six potato heaps, and sampled them for potato tuber moth at different locations at weekly intervals. Potato tuber moth infestation was significantly higher at the perimeter of the heaps than at their center, but it did not differ between bottom, mid-height, and top of the heaps. The proportion of potato tuber moth-infested potato tubers increased from 10 to 65% over the course of the experiment, and the mean number of potato tuber moth larvae per tuber increased from 0.25 to 2.50. Potato tuberworm populations increased sharply after 3, 6, and 9 wk of study, possibly corresponding to successive generations that developed within the heaps. This interpretation is supported by calculations of potato tuberworm generation length based on temperature data. Catches in pheromone traps that were placed near the heaps were not correlated (spatially and temporally) with potato tuberworm densities within heaps, hinting that migration among heaps did not considerably affect within-heap population dynamics. Potato tuberworm levels were not correlated with ambient temperatures, perhaps because of the warm, humid, and constant microclimate within the heaps. We discuss the significance of our findings for control efforts of the potato tuberworm.