Yersinia enterocolitica Infection and tcaA-Dependent Killing of Caenorhabditis elegans

Caenorhabditis elegans is a validated model to study bacterial pathogenicity. We report that Yersinia enterocolitica strains {"type":"entrez-nucleotide","attrs":{"text":"W22703","term_id":"1299536","term_text":"W22703"}}W22703 (biovar 2, serovar O:9) and WA314 (biovar 1B, serovar O:8) kill C. elegans when feeding on the pathogens for at least 15 min before transfer to the feeding strain Escherichia coli OP50. The killing by Yersinia enterocolitica requires viable bacteria and, in contrast to that by Yersinia pestis and Yersinia pseudotuberculosis strains, is biofilm independent. The deletion of tcaA encoding an insecticidal toxin resulted in an OP50-like life span of C. elegans, indicating an essential role of TcaA in the nematocidal activity of Y. enterocolitica. TcaA alone is not sufficient for nematocidal activity because E. coli DH5α overexpressing TcaA did not result in a reduced C. elegans life span. Spatial-temporal analysis of C. elegans infected with green fluorescent protein-labeled Y. enterocolitica strains showed that Y. enterocolitica colonizes the nematode intestine, leading to an extreme expansion of the intestinal lumen. By low-dose infection with {"type":"entrez-nucleotide","attrs":{"text":"W22703","term_id":"1299536","term_text":"W22703"}}W22703 or DH5α followed by transfer to E. coli OP50, proliferation of Y. enterocolitica, but not E. coli, in the intestinal lumen of the nematode was observed. The titer of {"type":"entrez-nucleotide","attrs":{"text":"W22703","term_id":"1299536","term_text":"W22703"}}W22703 cells within the worm increased to over 10⁶ per worm 4 days after infection while a significantly lower number of a tcaA knockout mutant was recovered. A strong expression of tcaA was observed during the first 5 days of infection. Y. enterocolitica WA314 (biovar 1B, serovar O:8) mutant strains lacking the yadA, inv, yopE, and irp1 genes known to be important for virulence in mammals were not attenuated or only slightly attenuated in their toxicity toward the nematode, suggesting that these factors do not play a significant role in the colonization and persistence of this pathogen in nematodes. In summary, this study supports the hypothesis that C. elegans is a natural host and nutrient source of Y. enterocolitica.Yersinia enterocolitica belongs to the family of Enterobacteriaceae and is a psychrotolerant human pathogen that causes gastrointestinal syndromes ranging from acute enteritis to mesenteric lymphadenitis (5). It infects a number of mammals, and swine was identified as a major source for human infection (6). A multiphasic life cycle, which comprises a free-living phase and several host-associated phases, including cold-blooded and warm-blooded hosts, appears to be characteristic for biovars 1B and 2 to 5 of Y. enterocolitica (7, 24).Nonmammalian host organisms including Dictyostelium discoideum, Drosophila melanogaster, or Caenorhabditis elegans are increasingly used to study host-pathogen interactions (16, 26). Due to the obvious parallels between the mammalian and invertebrate defense mechanisms, it has been suggested that the bacteria-invertebrate interaction has shaped the evolution of microbial pathogenicity (53). Several human pathogens including Gram-positive and Gram-negative bacteria infect and kill the soil nematode C. elegans when they are supplied as a nutrient source (42). For example, Streptococcus pneumoniae (4), Listeria monocytogenes (50), extraintestinal Escherichia coli (15), and Staphylococcus aureus (43) but not Bacillus subtilis have been shown to kill the nematode. Upon infection of C. elegans with Enterococcus faecalis, Gram-positive virulence-related factors as well as putative antimicrobials have been identified (20, 35). The extensive conservation in virulence mechanisms directed against invertebrates as well as mammals was demonstrated using a screen with Pseudomonas aeruginosa (30). In this study, 10 of 13 genes whose knockout attenuated the nematode killing were also required for full virulence in a mouse model, confirming the suitability of the C. elegans model to study bacterial pathogenicity. C. elegans is also colonized by Salmonella enterica serovar Typhimurium (S. Typhimurium). This process requires Salmonella virulence factors and was used to study the innate immune response of the nematode (1, 2, 49).The effect of pathogenic Yersinia spp. on C. elegans has also been investigated. It could be demonstrated that both Yersinia pestis and Yersinia pseudotuberculosis block food intake by creating a biofilm around the worm''s mouth (13, 27). This biofilm formation requires the hemin storage locus (hms) and has been suggested to be responsible for the blockage of the digestive tract following uptake by fleas, thus acting as a bacterial defense against predation by invertebrates. In a study with 40 Y. pseudotuberculosis strains, one-quarter of them caused an infection of C. elegans by biofilm formation on the worm head (27). In contrast, a similar effect was not observed following nematode infection with 15 Y. enterocolitica strains. Using a Y. pestis strain lacking the hms genes, it could be demonstrated that this mutant can infect and kill the nematode by a biofilm-independent mechanism that includes the accumulation of Y. pestis in the intestine of the worm (47). This pathogenesis model was applied to show that putative virulence factors such as YapH, OmpT, or a metalloprotease, Y3857, but not the virulence plasmids pCD1 and pPCP1, are required for Y. pestis virulence in C. elegans. Six yet unknown genes required for full virulence in C. elegans were also identified, and one of them appeared to be a virulence factor in the mouse infection model.C. elegans has not been used to study the pathogenicity properties of Y. enterocolitica, mainly due to the fact that many of its virulence factors are upregulated at 37°C in comparison to growth at lower temperatures while C. elegans cannot be cultivated at temperatures above 25°C. In this study, we examined for the first time the infection of C. elegans by Y. enterocolitica strains, demonstrating that this pathogen colonizes and kills C. elegans and that the insecticidal toxin TcaA, which is expressed only at ambient temperature, is required for full nematocidal activity.     

Mesenchymal stem cells in autoimmune diseases: hype or hope?

Intervention with mesenchymal stem cells (MSCs) represents a promising therapeutic tool in treatment-refractory autoimmune diseases. A new report by Schurgers and colleagues in a previous issue of Arthritis Research & Therapy sheds novel mechanistic insight into the pathways employed by MSCs to suppress T-cell proliferation in vitro, but, at the same time, indicates that MSCs do not influence T-cell reactivity and the disease course in an in vivo arthritis model. Such discrepancies between the in vitro and in vivo effects of potent cellular immune modulators should spark further research and should be interpreted as a sign of caution for the in vitro design of MSC-derived interventions in the setting of human autoimmune diseases.     

Polyamine and nitric oxide levels relate with morphogenetic evolution in somatic embryogenesis of <Emphasis Type="Italic">Ocotea catharinensis</Emphasis>

In this study we examined the effect of polyamines (PAs) putrescine (Put), spermidine (Spd) and spermine (Spm) on growth, morphology evolution, endogenous PAs levels and nitric oxide (NO) release in Ocotea catharinensis somatic embryo cultures. We observed that Spd and Spm reduced culture growth, permitted embryo morphogenetic evolution from the earliest to last embryo development stages, increased endogenous PAs levels, and induced NO release in O. catharinensis somatic embryos. On the other hand, Put had little effect on these parameters. Spd and Spm could successfully be used to promote somatic embryo maturation in O. catharinensis. The results suggest that Spd and Spm have an important role during the growth, development and morphogenetic evolution of somatic embryos, through alterations in the endogenous nitric oxide and PAs metabolism in this species.     

Analysis of compensatory beta-cell response in mice with combined mutations of Insr and Irs2

Type 2 diabetes results from impaired insulin action and beta-cell dysfunction. There are at least two components to beta-cell dysfunction: impaired insulin secretion and decreased beta-cell mass. To analyze how these two variables contribute to the progressive deterioration of metabolic control seen in diabetes, we asked whether mice with impaired beta-cell growth due to Irs2 ablation would be able to mount a compensatory response in the background of insulin resistance caused by Insr haploinsufficiency. As previously reported, approximately 70% of mice with combined Insr and Irs2 mutations developed diabetes as a consequence of markedly decreased beta-cell mass. In the initial phases of the disease, we observed a robust increase in circulating insulin levels, even as beta-cell mass gradually declined, indicating that replication-defective beta-cells compensate for insulin resistance by increasing insulin secretion. These data provide further evidence for a heterogeneous beta-cell response to insulin resistance, in which compensation can be temporarily achieved by increasing function when mass is limited. The eventual failure of compensatory insulin secretion suggests that a comprehensive treatment of beta-cell dysfunction in type 2 diabetes should positively affect both aspects of beta-cell physiology.     

Aquaporin-1 channel function is positively regulated by protein kinase C

Aquaporin-1 (AQP1) channels contribute to osmotically induced water transport in several organs including the kidney and serosal membranes such as the peritoneum and the pleura. In addition, AQP1 channels have been shown to conduct cationic currents upon stimulation by cyclic nucleotides. To date, the short term regulation of AQP1 function by other major intracellular signaling pathways has not been studied. In the present study, we therefore investigated the regulation of AQP1 by protein kinase C. AQP1 wild type channels were expressed in Xenopus oocytes. Water permeability was assessed by hypotonic challenges. Activation of protein kinase C (PKC) by 1-oleoyl-2-acetyl-sn-glycerol (OAG) induced a marked increase of AQP1-dependent water permeability. This regulation was abolished in mutated AQP1 channels lacking both consensus PKC phosphorylation sites Thr(157) and Thr(239) (termed AQP1 DeltaPKC). AQP1 cationic currents measured with double-electrode voltage clamp were markedly increased after pharmacological activation of PKC by either OAG or phorbol 12-myristate 13-acetate. Deletion of either Thr(157) or Thr(239) caused a marked attenuation of PKC-dependent current increases, and deletion of both phosphorylation sites in AQP1 DeltaPKC channels abolished the effect. In vitro phosphorylation studies with synthesized peptides corresponding to amino acids 154-168 and 236-250 revealed that both Thr(157) and Thr(239) are phosphorylated by PKC. Upon stimulation by cyclic nucleotides, AQP1 wild type currents exhibited a strong activation. This regulation was not affected after deletion of PKC phosphorylation sites in AQP1 DeltaPKC channels. In conclusion, this is the first study to show that PKC positively regulates both water permeability and ionic conductance of AQP1 channels. This new pathway of AQP1 regulation is independent of the previously described cyclic nucleotide pathway and may contribute to the PKC stimulation of AQP1-modulated processes such as endothelial permeability, angiogenesis, and urine concentration.     

Diagnostic Real-Time PCR Assays for the Detection of Emetic Bacillus cereus Strains in Foods and Recent Food-Borne Outbreaks

Cereulide-producing Bacillus cereus can cause an emetic type of food-borne disease that mimics the symptoms provoked by Staphylococcus aureus. Based on the recently discovered genetic background for cereulide formation, a novel 5′ nuclease (TaqMan) real-time PCR assay was developed to provide a rapid and sensitive method for the specific detection of emetic B. cereus in food. The TaqMan assay includes an internal amplification control and primers and a probe designed to target a highly specific part of the cereulide synthetase genes. Additionally, a specific SYBR green I assay was developed and extended to create a duplex SYBR green I assay for the one-step identification and discrimination of the two emesis-causing food pathogens B. cereus and S. aureus. The inclusivity and exclusivity of the assay were assessed using a panel of 100 strains, including 23 emetic B. cereus and 14 S. aureus strains. Different methods for DNA isolation from artificially contaminated foods were evaluated, and established real-time assays were used to analyze two recent emetic food poisonings in southern Germany. One of the food-borne outbreaks included 17 children visiting a day care center who vomited after consuming a reheated rice dish, collapsed, and were hospitalized; the other case concerned a single food-poisoning incident occurring after consumption of cauliflower. Within 2 h, the etiological agent of these food poisonings was identified as emetic B. cereus by using the real-time PCR assay.     

Germ-line DNA copy number variation frequencies in a large North American population

Genomic copy number variation (CNV) is a recently identified form of global genetic variation in the human genome. The Affymetrix GeneChip 100 and 500 K SNP genotyping platforms were used to perform a large-scale population-based study of CNV frequency. We constructed a genomic map of 578 CNV regions, covering approximately 220 Mb (7.3%) of the human genome, identifying 183 previously unknown intervals. Copy number changes were observed to occur infrequently (<1%) in the majority (>93%) of these genomic regions, but encompass hundreds of genes and disease loci. This North American population-based map will be a useful resource for future genetic studies. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Modeling inspiratory and expiratory steady-state velocity fields in the Sprague-Dawley rat nasal cavity

Distribution patterns of odorant molecules in the rat nasal olfactory region depend in large part on the detailed airflow patterns in the nasal cavity, which in turn depend on the anatomical structure. To investigate these flow patterns, we constructed an anatomically accurate finite element model of the right nasal cavity of the Sprague-Dawley rat based on horizontal (anterior-posterior) nasal cast cross sections. By numerically solving the fluid mechanical momentum and continuity equations using the finite element method, we studied the flow distribution and the complete velocity field for both inspiration and expiration throughout the nasal cavity under physiological flow rates of resting breathing and sniffing. Detailed velocity profiles, volumetric flow distributions, and streamline patterns for quasi-steady airflow are presented. S-shaped streamlines passing through the olfactory region are found to be less prevalent during expiratory than inspiratory flow leading to trapping and an increase in odorant molecule retention in the olfactory region during sniffing. The rat nasal velocity calculations will be used to study the distribution of odorant uptake onto the rat olfactory mucosa and compare it with the known anatomic location of some types of rat olfactory receptors.