Cyclitol metabolism is a central feature of Burkholderia leaf symbionts

The symbioses between plants of the Rubiaceae and Primulaceae families with Burkholderia bacteria represent unique and intimate plant–bacterial relationships. Many of these interactions have been identified through PCR-dependent typing methods, but there is little information available about their functional and ecological roles. We assembled 17 new endophyte genomes representing endophytes from 13 plant species, including those of two previously unknown associations. Genomes of leaf endophytes belonging to Burkholderia s.l. show extensive signs of genome reduction, albeit to varying degrees. Except for one endophyte, none of the bacterial symbionts could be isolated on standard microbiological media. Despite their taxonomic diversity, all endophyte genomes contained gene clusters linked to the production of specialized metabolites, including genes linked to cyclitol sugar analog metabolism and in one instance non-ribosomal peptide synthesis. These genes and gene clusters are unique within Burkholderia s.l. and are likely horizontally acquired. We propose that the acquisition of secondary metabolite gene clusters through horizontal gene transfer is a prerequisite for the evolution of a stable association between these endophytes and their hosts.     

Loss of DNA repair mechanisms in cardiac myocytes induce dilated cardiomyopathy

Cardiomyopathy is a progressive disease of the myocardium leading to impaired contractility. Genotoxic cancer therapies are known to be potent drivers of cardiomyopathy, whereas causes of spontaneous disease remain unclear. To test the hypothesis that endogenous genotoxic stress contributes to cardiomyopathy, we deleted the DNA repair gene Ercc1 specifically in striated muscle using a floxed allele of Ercc1 and mice expressing Cre under control of the muscle-specific creatinine kinase (Ckmm) promoter or depleted systemically (Ercc1^−/D mice). Ckmm-Cre^+/−;Ercc1^−/fl mice expired suddenly of heart disease by 7 months of age. As young adults, the hearts of Ckmm-Cre^+/−;Ercc1^−/fl mice were structurally and functionally normal, but by 6-months-of-age, there was significant ventricular dilation, wall thinning, interstitial fibrosis, and systolic dysfunction indicative of dilated cardiomyopathy. Cardiac tissue from the tissue-specific or systemic model showed increased apoptosis and cardiac myocytes from Ckmm-Cre^+/-;Ercc1^−/fl mice were hypersensitive to genotoxins, resulting in apoptosis. p53 levels and target gene expression, including several antioxidants, were increased in cardiac tissue from Ckmm-Cre^+/−;Ercc1^−/fl and Ercc1^−/D mice. Despite this, cardiac tissue from older mutant mice showed evidence of increased oxidative stress. Genetic or pharmacologic inhibition of p53 attenuated apoptosis and improved disease markers. Similarly, overexpression of mitochondrial-targeted catalase improved disease markers. Together, these data support the conclusion that DNA damage produced endogenously can drive cardiac disease and does so mechanistically via chronic activation of p53 and increased oxidative stress, driving cardiac myocyte apoptosis, dilated cardiomyopathy, and sudden death.     

Epidermal Growth Factor Inhibits Gap Junctional Communication and Stimulates Serine-Phosphorylation of Connexin43 in WB Cells by a Protein Kinase C-Independent Mechanism

Epidermal growth factor (EGF) stimulated the phosphorylation of connexin43 (Cx43) in WB cells as evidenced by the formation of multiple irnmunoreactive Cx43 proteins of higher molecular mass which were abolished by treatment with alkaline phosphatase. Phosphorylation of Cx43 occurred within 10 min of EGF stimulation, was sustained for 1 h, and was associated with almost complete inhibition of gap junctional communication in these cells. EGF-induced phosphorylation and communication inhibition were retained in cells pretreated with phorbol 12-myristate 13-acetate (PMA) to deplete protein kinase C. These results show that the EGF inhibition of communication is tightly linked to protein kinase C-independent phosphorylation of Cx43. Further, Cx43 phosphorylated in the presence of EGF did not react with phosphotyrosine antibodies and in ³²P_i incorporation experiments was shown to contain only phosphoserine indicating that the tyrosine kinase activity of the EGF receptor was not directly involved.     

Induction of detoxification enzymes in phytophagous insects: Role of insecticide synergists,larval age,and species

Five insecticide synergists, all of which were either methylenedioxyphenyl compounds or analogs, were compared as to their effect on cytochrome P450 monooxygenase induction caused by an allelochemical in fall armyworm larvae. Feeding the synergists (piperonyl butoxide, safrole, isosafrole, MGK 264, and myristicin) individually to the larvae caused decreases in the microsomal aldrin epoxidase activities ranging from 38% to 74% when compared with controls. Feeding indole-3-carbinol resulted in a 4-fold increase in the microsomal epoxidase activity. However, cotreatment of any of the synergists and the inducer completely eliminated the induction. Sixth instar larvae were more inducible than second instar larvae with respect to microsomal epoxidase and glutathione transferase in the fall armyworm. Enzyme inducibility varied widely among the seven phytophagous Lepidoptera examined. When indole-3-carbinol was used as an inducer of microsomal epoxidase, the extent of inducibility of the enzyme was fall armyworm > velvetbean caterpillar > corn earworm > beet armyworm > tobacco budworm > cabbage looper > diamondback moth. When indole-3-acetonitrile was used as an inducer, the inducibility of glutathione transferase was fall armyworm > beet armyworm > corn earworm > cabbage looper > velvetbean caterpillar > tobacco budworm > diamondback moth. Inducibility of five microsomal oxidase systems also varied considerably in the corn earworm, indicating the multiplicity of cytochrome P450 in this species. Microsomal epoxidase and glutathione transferase were induced by cruciferous host plants such as cabbage and their allelochemicals in diamondback moth larve. © 1993 Wiley-Liss, Inc.     

Human Menkes X-chromosome disease and the staphylococcal cadmium-resistance ATPase: a remarkable similarity in protein sequences

A search with the proposed amino acid translation product from the new ‘candidate gene’ for human Menkes disease against protein sequence libraries showed a remarkable similarity to that for the cadmium efflux ATPase from Staphylococcus aureus resistance plasmids. The Menkes sequence appears closer to the CadA Cd²⁺ sequence than to P-type ATPases from animal sources. Menkes syndrome is an X-chromosome invariably fatal disease that results from abberant copper metabolism. The gene that is defective in Menkes patients, i.e. the Menkes candidate gene, encodes a P-type ATPase, whose properties satisfactorily explain the phenotype of the disease. P-type ATPases are all cation pumps, either for uptake (e.g. the bacterial Kdp K⁺ ATPase), for efflux (e.g. the muscle sarcoplasmic reticulum Ca²⁺ ATPase), or for cation exchange (e.g. the animal cell Na⁺/K⁺ ATPase). These enzymes have a conserved aspartate residue that is transiently phosphorylated from ATP during the transport cycle, hence the name ‘P-type’ ATPase. The Menkes sequence shares with the staphylococcal CadA ATPase those regions common to all P-type ATPases and also an N-terminal dithiol region that was proposed to be a ‘metal-binding motif’. There are one or two copies of this motif in the available CadA sequences and six copies in the Menkes sequence.     

The caecilian amphibian Scolecomorphus kirkii Boulenger as prey of the burrowing asp Atractaspis aterrima Günther: trophic relationships of fossorial vertebrates

A report is given of an adult caecilian, Scolecomorphus kirkii, found in the gut of a specimen of the snake Atractaspis aterrima from the Udzungwa Mountains, Tanzania. Both predator and prey are largely fossorial in soil, and their ecology is poorly known, such that this is the first reported predator of any scolecomorphid caecilian. The caecilian was ingested head first and much of the flesh from the anterior of the specimen had been digested. The prey/predator mass ratio is 0.48. This value is substantially higher than reported for A. aterrima from West Africa, and refutes the notion that this species feeds only on small prey. Most reported predators of caecilians are snakes, and a brief review is presented.