VEGF receptor 2/‐3 heterodimers detected in situ by proximity ligation on angiogenic sprouts

The vascular endothelial growth factors VEGFA and VEGFC are crucial regulators of vascular development. They exert their effects by dimerization and activation of the cognate receptors VEGFR2 and VEGFR3. Here, we have used in situ proximity ligation to detect receptor complexes in intact endothelial cells. We show that both VEGFA and VEGFC potently induce formation of VEGFR2/‐3 heterodimers. Receptor heterodimers were found in both developing blood vessels and immature lymphatic structures in embryoid bodies. We present evidence that heterodimers frequently localize to tip cell filopodia. Interestingly, in the presence of VEGFC, heterodimers were enriched in the leading tip cells as compared with trailing stalk cells of growing sprouts. Neutralization of VEGFR3 to prevent heterodimer formation in response to VEGFA decreased the extent of angiogenic sprouting. We conclude that VEGFR2/‐3 heterodimers on angiogenic sprouts induced by VEGFA or VEGFC may serve to positively regulate angiogenic sprouting.     

Evidence for myofibril remodeling as opposed to myofibril damage in human muscles with DOMS: an ultrastructural and immunoelectron microscopic study

The myofibrillar and cytoskeletal alterations observed in delayed onset muscle soreness (DOMS) caused by eccentric exercise are generally considered to represent damage. By contrast our recent immunohistochemical studies suggested that the alterations reflect myofibrillar remodeling (Yu and Thornell 2002; Yu et al. 2003). In the present study the same human muscle biopsies were further analyzed with transmission electron microscopy and immunoelectron microscopy. We show that the ultrastructural hallmarks of DOMS, Z-disc streaming, Z-disc smearing, and Z-disc disruption were present in the biopsies and were significantly more frequent in biopsies taken 2–3 days and 7–8 days after exercise than in those from controls and 1 h after exercise. Four main types of changes were observed: amorphous widened Z-discs, amorphous sarcomeres, double Z-discs, and supernumerary sarcomeres. We confirm by immunoelectron microscopy that the main Z-disc protein alpha-actinin is not present in Z-disc alterations or in the links of electron-dense material between Z-discs in longitudinal register. These alterations were related to an increase of F-actin and desmin, where F-actin was present within the strands of amorphous material. Desmin, on the other hand, was seen in less dense regions of the alterations. Our results strongly support that the myofibrillar and cytoskeletal alterations, considered to be the hallmarks of DOMS, reflect an adaptive remodeling of the myofibrils.     

Multiple-locus variable-number tandem-repeats analysis of Salmonella enterica subsp. enterica serovar Typhimurium using PCR multiplexing and multicolor capillary electrophoresis

The multiple-locus variable-number tandem-repeats analysis (MLVA) method is currently being used as the primary typing tool for Salmonella enterica subsp. enterica serovar Typhimurium (S. Typhimurium) isolates in our laboratory. Our published initial MLVA was performed using a single fluorescent dye and the different patterns were assigned from gel images. Here we present a new and significantly improved assay using multiple dye colors, enhanced PCR multiplexing and the introduction of two new loci for better adaptation to capillary electrophoresis with increased speed. The different MLVA patterns are now based on allele sizes entered as character values, thus removing the uncertainties introduced when analyzing band patterns from gel images. We additionally propose an easy numbering scheme for the identification of separate isolates that will facilitate exchange of typing data. A total of 106 human, bird, animal and food isolates of S. Typhimurium, including 16 with definite type (DT) 104, were used for the development of the improved MLVA. The method is based on capillary separation of multiplexed PCR products from five VNTR loci in the S. Typhimurium genome labeled with multiple fluorescent dyes. The different alleles at each locus were then assigned allele numbers, which were used for strain comparison.     

Rat intestinal ceramidase: purification, properties, and physiological relevance

Neutral ceramidase activity has previously been identified in the intestinal mucosa and gut lumen and postulated to be important in the digestion of sphingolipids. It is found throughout the intestine but has never been fully characterized. We have purified rat intestinal neutral ceramidase from an eluate obtained by perfusing the intestinal lumen with 0.9% NaCl and 3 mM sodium taurodeoxycholate. Using a combination of acetone precipitation and ion-exchange, hydrophobic-interaction, and gel chromatographies, we obtained a homogenous enzyme protein with a molecular mass of approximately 116 kDa. The enzyme acts on both [14)]octanoyl- and [14C]palmitoyl-sphingosine in the presence of glycocholic and taurocholic acid and the bile salt analog 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate but is inhibited by 2 mM or more of other bile salts. It is a glycosylated protein stable to trypsin and chymotrypsin exposure, is not influenced by Ca2+, Mg2+, or Mn2+, and is inhibited by Zn2+ and Cu2+. Mass fragmentographic analysis identified 12 fragments covering 17.5% of the sequence for neutral/alkaline ceramidase 2 purified (Mitsutake S, Tani M, Okino N, Mori K, Ichinose S, Omori A, Iida H, Nakamura T, and Ito M. J Biol Chem 276: 26249-262459, 2001) from rat kidney and located in apical membrane of renal tubular cells. Intestinal and kidney ceramidases also have similar molecular mass and ion dependence. Intestinal ceramidase thus is a neutral ceramidase 2 released by bile salts and resistant to pancreatic proteases. It is well suited to metabolize ceramide formed from dietary and brush border sphingolipids to generate other bioactive sphingolipid messengers.     

Postreplicative recruitment of cohesin to double-strand breaks is required for DNA repair

Chromosome stability depends on accurate chromosome segregation and efficient DNA double-strand break (DSB) repair. Sister chromatid cohesion, established during S phase by the protein complex cohesin, is central to both processes. In the absence of cohesion, chromosomes missegregate and G2-phase DSB repair fails. Here, we demonstrate that G2-phase repair also requires the presence of cohesin at the damage site. Cohesin components are shown to be recruited to extended chromosome regions surrounding DNA breaks induced during G2. We find that in the absence of functional cohesin-loading proteins (Scc2/Scc4), the accumulation of cohesin at DSBs is abolished and repair is defective, even though sister chromatids are connected by S phase generated cohesion. Evidence is also provided that DSB induction elicits establishment of sister chromatid cohesion in G2, implicating that damage-recruited cohesin facilitates DNA repair by tethering chromatids.     

The diversity of Listeria monocytogenes strains from 10 Icelandic sheep farms

AIMS: The purpose of this study was to examine the diversity of Listeria monocytogenes strains from healthy sheep, winter feed and environment of sheep farms in Iceland. METHODS AND RESULTS: A total of 104 L. monocytogenes isolates from animals, winter feed and environment on 10 Icelandic sheep farms were compared by serotyping, ribotyping, and pulsed-field gel electrophoresis with ApaI and AscI. The isolates were divided into 24 genotypes, all identified as serovars 1/2a, 1/2b, or 4b. Nine genotypes were detected on more than one farm. On three of the farms there seemed to be a dominant strain of L. monocytogenes. Isolates from incidents of listeriosis in animals occurring on two of the farms belonged to the genotype most commonly found on the particular farm. Nine of the 24 genotypes found on the sheep farms have been associated with disease in animals and/or humans elsewhere in Iceland. CONCLUSIONS: Certain strains of L. monocytogenes seem to be widely distributed on Icelandic sheep farms. On some farms there appears to be a dominant strain of L. monocytogenes. Incidents of listeriosis in animals may tend to be associated with strains commonly found on the farm. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrates the diversity of L. monocytogenes present in healthy sheep and their environment.     

Switching the mode of metabolism in the yeast Saccharomyces cerevisiae

The biochemistry of most metabolic pathways is conserved from bacteria to humans, although the control mechanisms are adapted to the needs of each cell type. Oxygen depletion commonly controls the switch from respiration to fermentation. However, Saccharomyces cerevisiae also controls that switch in response to the external glucose level. We have generated an S. cerevisiae strain in which glucose uptake is dependent on a chimeric hexose transporter mediating reduced sugar uptake. This strain shows a fully respiratory metabolism also at high glucose levels as seen for aerobic organisms, and switches to fermentation only when oxygen is lacking. These observations illustrate that manipulating a single step can alter the mode of metabolism. The novel yeast strain is an excellent tool to study the mechanisms underlying glucose-induced signal transduction.