Inhibition of nitrate consumption by nitrite in entrapped Chlamydomonas reinhardtii cells.

Whereas in freely suspended cell cultures growing photoautotrophically under non-limiting carbon conditions nitrite and nitrate were simultaneously consumed after ammonium consumption was complete, in alginate-entrapped cell cultures a sequential consumption of nitrite (first) and nitrate was observed after ammonium had almost been fully removed. In this paper results are reported that show inhibition of nitrate consumption by nitrite in immobilized cells. However no inhibition of nitrate active transport was observed. The sequential consumption of ammonium, nitrite and nitrate by Ca-alginate immobilized cells is explained on the basis of local ammonium accumulation due to its photoproduction by photorespiration, that could be caused by the increase of the O2/CO2 ratio around the entrapped cells. Measurements of light-dependent oxygen production (LDOP) and activity levels of nitrogen assimilation enzymes, including nitrite reductase (NiR) and glutamine synthetase (GS) in immobilized cells, determined under photorespiration stimulating conditions, are shown that support this explanation.     

Epidemiology of candidemia in Spain - Multicenter study

The results of the epidemiological study on candidemias with the highest number of cases carried out in Spain is presented. This study is included in the Epidemiological Survey of Candidemia in Europe supported by the ECMM in which another five countries take part. In the Spanish study, 19 hospitals participated, 290 candidemia episodes were analysed (80 in children under 15 years and 210 in adults), 293 strains of yeasts being isolated. Both in children and in adults, the risks factors more frequently observed were the intravenous catheter and previous antibiotic therapy. In adults, the most habitual underlying disease was the solid tumor and, in children, hematological diseases. Candida albicans was the most prevalent species isolated in adults (46.1%) and Candida parapsilosis in children (50%). As part of the therapy, the intravenous line was removed and antifungal treatment was prescribed to 74% and 92.5% of children, respectively and to 43.8% and 73.8% of adults. The antifungal agent of election in adults was fluconazole (54.8%) and liposomal amphotericin B (58.1%) in children. The global mortality of the study was 38.9%, which for ages was major in adults (41.4%) than in children (38.7%). The geographical distribution of the isolated species was homogeneous, C. albicans being the predominant species, with the exception of Galicia and Extremadura where C. parapsilosis was the most frequent.     

Cell-cycle-dependent regulation of CNT1, a concentrative nucleoside transporter involved in the uptake of cell-cycle-dependent nucleoside-derived anticancer drugs

Most nucleoside-derived anticancer drugs are taken up by the high-affinity Na-dependent nucleoside transporter CNT1. Since such drugs are to some extent cell-cycle-dependent in their cytotoxic action, we examined the relationship between CNT1 expression and cell-cycle progression in the rat hepatoma cell line FAO. Cell cultures were synchronized either at late G1 or early S stages by combining mimosin treatment with either previous synchronization or not by serum starvation. Cell-cycle progression was then assessed by measuring [methyl-3H]thymidine incorporation into DNA and monitoring cyclin E and A protein levels. In these conditions, CNT1 protein amounts increase at the G1-S transition. When cells were synchronized using hydroxyurea (HU), which directly interacts with nucleotide metabolism by inhibiting ribonucleotide reductase, CNT1 protein amounts increased in synchronized cells and remained high during cell-cycle progression. These data indicate that CNT1 adapts to cell-cycle progression and responds to nucleos(t)ide metabolism status, a feature that might contribute to the cytotoxic action of cell-cycle-dependent anticancer drugs.     

Taurine levels and localisation in the stratified squamous epithelia

The content and distribution of the amino acid taurine in squamous epithelia were studied using high-performance liquid chromatography and immunohistochemical methods. Quantitative analysis demonstrated that taurine was highly concentrated in the epidermis (5.49 mumol/g fresh tissue in the hairless skin of the hind footpad of the rat), although the values in the isolated stratum corneum were extremely low (< 0.073 mumol/g in the horny layer of the same skin area). No other analysed amino acid (such as glutamate, glutamine, glycine or alanine) showed this specific pattern of distribution. The immunohistochemical study revealed that in the dog and rat epidermis, taurine was present in the keratinocytes of the granular and upper spinous layers. The basal layer, lower spinous layer and stratum corneum were immunonegative. A similar immunostaining pattern was found in the epithelia of the different organs studied: the mouth, tongue and oesophagus of the dog and rat, the rat forestomach and the rat corneal epithelium. Other cell types, such as sebaceous and muscle cells, were immunolabelled. The existence of a circulating pool of taurine in the epidermis (via taurine release from keratinocytes before they reach the horny layer and its uptake by nearby cells) and its possible roles in these cells are discussed.     

Sedimentation loss of phytoplankton cells from the mixed layer: effects of turbulence levels

In this paper, we describe a study of the role of turbulencein the loss by sedimentation of phytoplankton cells from themixed layer. The approach presented allows the quantificationof the sedimentation rate of phytoplankton in the whole rangeof turbulence levels of this layer. Two types of phytoplanktercan be distinguished according to the effect that turbulencecan exert on their sedimentation rate. The rate of those cellswhose settling velocity is lower than –1 m day^–1will not be modified by turbulence. The sedimentation rate ofcells with higher settling velocities can, however, be modifiedby the level of turbulence. A set of dimensionless numbers isgiven to delimit several processes that are important in thedynamics of phytoplankton sedimentation in a turbulent regime.The use of these dimensionless numbers suggests that an increasein the turbulence level in the mixed layer does not always implya decrease in the sedimentation rate of phytoplankton cells.     

Robustness and stability of the gene regulatory network involved in DV boundary formation in the Drosophila wing

Gene regulatory networks have been conserved during evolution. The Drosophila wing and the vertebrate hindbrain share the gene network involved in the establishment of the boundary between dorsal and ventral compartments in the wing and adjacent rhombomeres in the hindbrain. A positive feedback-loop between boundary and non-boundary cells and mediated by the activities of Notch and Wingless/Wnt-1 leads to the establishment of a Notch dependent organizer at the boundary. By means of a Systems Biology approach that combines mathematical modeling and both in silico and in vivo experiments in the Drosophila wing primordium, we modeled and tested this regulatory network and present evidence that a novel property, namely refractoriness to the Wingless signaling molecule, is required in boundary cells for the formation of a stable dorsal-ventral boundary. This new property has been validated in vivo, promotes mutually exclusive domains of Notch and Wingless activities and confers stability to the dorsal-ventral boundary. A robustness analysis of the regulatory network complements our results and ensures its biological plausibility.     

Invasive and adherent bacterial pathogens co-Opt host clathrin for infection

Infection by the bacterium Listeria monocytogenes depends on host cell clathrin. To determine whether this requirement is widespread, we analyzed infection models using diverse bacteria. We demonstrated that bacteria that enter cells following binding to cellular receptors (termed "zippering" bacteria) invade in a clathrin-dependent manner. In contrast, bacteria that inject effector proteins into host cells in order to gain entry (termed "triggering" bacteria) invade in a clathrin-independent manner. Strikingly, enteropathogenic Escherichia coli (EPEC) required clathrin to form actin-rich pedestals in host cells beneath adhering bacteria, even though this pathogen remains extracellular. Furthermore, clathrin accumulation preceded the actin rearrangements necessary for Listeria entry. These data provide evidence for a clathrin-based entry pathway allowing internalization of large objects (bacteria and ligand-coated beads) and used by "zippering" bacteria as part of a general mechanism to invade host mammalian cells. We also revealed a nonendocytic role for clathrin required for extracellular EPEC infections.     

Dynamic emergence of the mesenchymal CD44CD24 phenotype in HER2-gene amplified breast cancer cells with de novo resistance to trastuzumab (Herceptin)

Evidence is mounting that the occurrence of the CD44^pos/CD24^neg/low cell population, which contains potential breast cancer (BC) stem cells, could explain BC clinical resistance to HER2-targeted therapies. We investigated whether de novo refractoriness to the anti-HER2 monoclonal antibody trastuzumab (Tzb; Herceptin) may relate to the dynamic regulation of the mesenchymal CD44^pos/CD24^neg/low phenotype in HER2-positive BC. We observed that the subpopulation of Tzb-refractory JIMT-1 BC cells exhibiting CD44^pos/CD24^neg/low-surface markers switched with time. Low-passage JIMT-1 cell cultures were found to spontaneously contain ∼10% of cells bearing the CD44^pos/CD24^neg/low immunophenotype. Late-passage (>60) JIMT-1 cultures accumulated ∼80% of CD44^pos/CD24^neg/low cells and closely resembled the CD44^pos/CD24^neg/low-enriched (∼85%) cell population constitutively occurring in HER2-negative MDA-MB-231 mesenchymal BC cells. Dynamic expression of mesenchymal markers was not limited to CD44/CD24 because high-passages of JIMT-1 cells exhibited also reduced expression of the HER2 protein and over-secretion of pro-invasive/metastatic chemokines and metalloproteases. Accordingly, late-passage JIMT-1 cells displayed an exacerbated migratogenic phenotype in plastic, collagen, and fibronectin substrates. Intrinsic genetic plasticity to efficiently drive the emergence of the CD44^pos/CD24^neg/low mesenchymal phenotype may account for de novo resistance to HER2 targeting therapies in basal-like BC carrying HER2 gene amplification.