Temperature-Sensitive Modification and Restriction Phenotypes of an Escherichia coli dnaD Mutant

A mutant of Escherichia coli temperature-sensitive for deoxyribonucleic acid synthesis, dnaD, was found to have temperature-sensitive modification and restriction phenotypes. In contrast to the original observation by Carl (1970), the mutant could support the growth of λ phage at 41 C. However, the λ phages thus produced were able to form plaques with normal plating efficiency only on E. coli C, a restriction-less strain, but not on E. coli K. Since the λ phages produced in the mutant at 30 C could form plaques equally well on both E. coli strains, it was concluded that the dnaD mutant has a temperature-sensitive modification phenotype. Furthermore, since the dnaD mutant allowed some growth of unmodified λ·C phages at 41 C but less at 30 C, the mutant is also temperature sensitive in restriction. The relationship, if any, between temperature-sensitive deoxyribonucleic acid synthesis and temperature-sensitive modification-restriction in the dnaD mutant is not known. Similar experiments were done with three dnaC mutants and one dnaA mutant. Two dnaC mutants were found to have altered restriction phenotypes at 41 C, but none of the mutants were defective in modification.     

THE FUNCTION OF HEAT-SHOCK PROTEINS IN STRESS TOLERANCE

We earlier demonstrated that hsp68 is deficiently induced upon stress in the glucocorticoid-resistant, dedifferentiated Reuber rat hepatoma clone 2 cells, but is strongly activated in the differentiated, glucocorticoid-sensitive Faza 967 cells from which clone 2 was derived. We used the two cell types to address the questions whether hsp68 is specifically involved in the development of thermotolerance and/or thermoresistance or drug resistance. Our experiments show that clone 2 cells were not protected from the killing effect of heat by pretreatment with sodium arsenite, whereas Faza 967 cells were. These results strongly suggest a role of hsp68 in the development of thermotolerance in hepatoma cells. Stable heat-resistant variants of clone 2 cells were also isolated, where an increased basal expression of several hsps was observed together with the (at least partial) restoration of the heat-inducibility of hsp68. These results suggest that several hsps are needed to protect the critical biological processes at high temperature. The heat-resistant hepatoma cells also became resistant to several anticancer drugs. The multidrug resistance of the hepatoma variants correlates with the overexpression of the plasma membrane P-glycoprotein. Our results showing that severely stressed hepatoma cells overexpressed the mdr gene(s) raise the possibility that the P-gp may participate in protection against environmental stress such as heat.     

Functionally distinct PI 3-kinase pathways regulate myelination in the peripheral nervous system

The PI 3-kinase (PI 3-K) signaling pathway is essential for Schwann cell myelination. Here we have characterized PI 3-K effectors activated during myelination by probing myelinating cultures and developing nerves with an antibody that recognizes phosphorylated substrates for this pathway. We identified a discrete number of phospho-proteins including the S6 ribosomal protein (S6rp), which is down-regulated at the onset of myelination, and N-myc downstream-regulated gene-1 (NDRG1), which is up-regulated strikingly with myelination. We show that type III Neuregulin1 on the axon is the primary activator of S6rp, an effector of mTORC1. In contrast, laminin-2 in the extracellular matrix (ECM), signaling through the α6β4 integrin and Sgk1 (serum and glucocorticoid-induced kinase 1), drives phosphorylation of NDRG1 in the Cajal bands of the abaxonal compartment. Unexpectedly, mice deficient in α6β4 integrin signaling or Sgk1 exhibit hypermyelination during development. These results identify functionally and spatially distinct PI 3-K pathways: an early, pro-myelinating pathway driven by axonal Neuregulin1 and a later-acting, laminin–integrin-dependent pathway that negatively regulates myelination.     

Exercise Increases Markers of Spermatogenesis in Rats Selectively Bred for Low Running Capacity

The oxidative stress effect of exercise training on testis function is under debate. In the present study we used a unique rat model system developed by artificial selection for low and high intrinsic running capacity (LCR and HCR, respectively) to evaluate the effects of exercise training on apoptosis and spermatogenesis in testis. Twenty-four 13-month-old male rats were assigned to four groups: control LCR (LCR-C), trained LCR (LCR-T), control HCR (HCR-C), and trained HCR (HCR-T). Ten key proteins connecting aerobic exercise capacity and general testes function were assessed, including those that are vital for mitochondrial biogenesis. The VO2 max of LCR-C group was about 30% lower than that of HCR-C rats, and the SIRT1 levels were also significantly lower than HCR-C. Twelve weeks of training significantly increased maximal oxygen consumption in LCR by nearly 40% whereas HCR remained unchanged. LCR-T had significantly higher levels of peroxisome proliferator-activated receptor-gamma coactivator-1 (PGC-1α), decreased levels of reactive oxygen species and increased acetylated p53 compared to LCR-C, while training produced no significant changes for these measures in HCR rats. BAX and Blc-2 were not different among all four groups. The levels of outer dense fibers -1 (Odf-1), a marker of spermatogenesis, increased in LCR-T rats, but decreased in HCR-TR rats. Moreover, exercise training increased the levels of lactate dehydrogenase C (LDHC) only in LCR rats. These data suggest that rats with low inborn exercise capacity can increase whole body oxygen consumption and running exercise capacity with endurance training and, in turn, increase spermatogenesis function via reduction in ROS and heightened activity of p53 in testes.     

Multivariate exploratory tools for microarray data analysis

The ultimate success of microarray technology in basic and applied biological sciences depends critically on the development of statistical methods for gene expression data analysis. The most widely used tests for differential expression of genes are essentially univariate. Such tests disregard the multidimensional structure of microarray data. Multivariate methods are needed to utilize the information hidden in gene interactions and hence to provide more powerful and biologically meaningful methods for finding subsets of differentially expressed genes. The objective of this paper is to develop methods of multidimensional search for biologically significant genes, considering expression signals as mutually dependent random variables. To attain these ends, we consider the utility of a pertinent distance between random vectors and its empirical counterpart constructed from gene expression data. The distance furnishes exploratory procedures aimed at finding a target subset of differentially expressed genes. To determine the size of the target subset, we resort to successive elimination of smaller subsets resulting from each step of a random search algorithm based on maximization of the proposed distance. Different stopping rules associated with this procedure are evaluated. The usefulness of the proposed approach is illustrated with an application to the analysis of two sets of gene expression data.     

Tyrosine 3 of poliovirus terminal peptide VPg(3B) has an essential function in RNA replication in the context of its precursor protein, 3AB

Poliovirus (PV) VPg is a genome-linked protein that is essential for the initiation of viral RNA replication. It has been well established that RNA replication is initiated when a molecule of UMP is covalently linked to the hydroxyl group of a tyrosine (Y3) in VPg by the viral RNA polymerase 3D(pol), but it is not yet known whether the substrate for uridylylation in vivo is the free peptide itself or one of its precursors. The aim of this study was to use complementation analyses to obtain information about the true in vivo substrate for uridylylation by 3D(pol). Previously, it was shown that a VPg mutant, in which tyrosine 3 and threonine 4 were replaced by phenylalanine and alanine (3F4A), respectively, was nonviable. We have now tested whether wild-type forms of proteins 3B, 3BC, 3BCD, 3AB, 3ABC, and P3 provided either in trans or in cis could rescue the replication defect of the VPg(3F4A) mutations in the PV polyprotein. Our results showed that proteins 3B, 3BC, 3BCD, and P3 were unable to complement the RNA replication defect in dicistronic PV or dicistronic luciferase replicons in vivo. However, cotranslation of the P3 precursor protein allowed rescue of RNA replication of the VPg(3F4A) mutant in an in vitro cell-free translation-RNA replication system, but only poor complementation was observed when 3BC, 3AB, 3BCD, or 3ABC proteins were cotranslated in the same assay. Interestingly, only protein 3AB but not 3B and 3BC, when provided in cis by insertion of a wild-type 3AB coding sequence between the P2 and P3 domains of the polyprotein, supported the replication of the mutated genome in vivo. Elimination of cleavage between 3A and 3B in the complementing 3AB protein, however, led to a complete lack of RNA replication. Our results suggest that (i) VPg has to be delivered to the replication complex in the form of a large protein precursor (P3) to be fully functional in replication; (ii) the replication complex formed during PV replication in vivo is essentially inaccessible to proteins provided in trans, even if the complementing protein is translated from a different cistron of the same RNA genome; (iii) 3AB is the most likely precursor of VPg; and (iv) Y3 of VPg has an essential function in RNA replication in the context of both VPg and 3AB.     

Phylogenetic relationships in the Neotropical tribe Hamelieae (Rubiaceae,Cinchonoideae) and comments on its generic limits

Our molecular phylogenetic analyses shed some light on the evolutionary relationships within the Hamelieae tribe. Phylogenetic reconstructions based on Internal Transcribed Spacer and trnL-F sequence data revealed the presence of three distinct evolutionary lineages. The first clade includes Hamelia and Syringantha, the second clade includes Deppea s.l. (including Bellizinca, Csapodya, and Edithea), and the third clade includes Pinarophyllon, Deppeopsis, Hoffmannia,Pseudomiltemia, Plocaniophyllon, Omiltemia, and Renistipula. The phylogenetic analysis re-evaluated some taxonomical combinations. The transfer of Deppeopsistaxa from Deppea s.l. is supported, but however, the monophyly of the genus is not. The transfer of Renistipula from Rondeletieae is also highly supported. BothCsapodya and Edithea species form a well-defined group among Deppea s.l. with high posterior probabilities, allowing to reconsider the exclusion or integration of these taxa to Deppea.