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.     

Phylogenetic diversification of immunoglobulin genes and the antibody repertoire

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.      

EXPERIMENTAL STUDIES OF THE EVOLUTIONARY SIGNIFICANCE OF SEXUAL REPRODUCTION. VI. A GREENHOUSE TEST OF THE SIB-COMPETITION HYPOTHESES

This study tests the hypothesis that competition among groups of sexual and asexual siblings generates an advantage for sexual females. Individual tillers of Anthoxanthum odoratum were planted singly, among other siblings from the same family, and among groups of sexual and asexual siblings from different families in pots in an unheated greenhouse. Unlike previous field experiments, there was little difference between the performance of sexual and clonal tillers after two years, despite strong treatment effects and high mortality. The results demonstrate that sib competition does not generate an advantage for sexual reproduction in biotically simple environments.     

Febrile Gastroenteritis Due to Salmonella thompson—Report of an Outbreak

Salmonella thompson, a common pathogen of poultry, has received scant attention as a cause of human gastroenteritis. At least 45 persons were infected with S thompson in Sacramento, California, after eating at a chicken restaurant and 38 became symptomatic. Ten required admission to hospital, and all were treated with antibiotics and improved. In 19 cases cultures of stool specimens for S thompson over a 60-day period showed slower but statistically insignificant differences in salmonellal elimination in 7 patients who received antibiotics when compared with 12 who were untreated. We report this outbreak to increase awareness of the virulence and prevalence of gastroenteritis due to S thompson.     

Effect of noncoliforms on coliform detection in potable groundwater: improved recovery with an anaerobic membrane filter technique

A total of 529 well and distribution potable water samples were analyzed for total coliforms by the most-probable-number and membrane filter (MF) techniques. Standard plate count bacteria and MF noncoliform bacteria were also enumerated. Frequency of coliform detection, turbidity in most-probable-number tubes, and extensive overgrowth by noncoliforms on MF filters were directly proportional to standard plate counts. Recovery of coliforms was greatest by the MF method at low (less than 100 CFU/ml) standard plate count densities and better by the most-probable-number method (confirming gas and turbid tube) at high (greater than 500 CFU/ml) standard plate count densities. In the latter case, overgrowth by noncoliforms on MF filters suppressed sheen development and, in turn, masked coliform detection. Of 341 atypical (no sheen) MF colonies verified by parallel inoculation of lauryl sulfate broth and billiant green-bile broth, 156 were aerogenic in the latter medium. Of atypical isolates, 84% were identified as either Citrobacter or Enterobacter species. A 4.3-fold reduction in numbers of overgrown MF filters and an 2.2-fold increase in numbers of coliforms recovered from 127 water samples was accomplished by anaerobic incubation of MF cultures. This anaerobic modification of the standard MF technique significantly reduced overgrowth and enhanced recovery of coliforms from potable groundwater. This technique is simple, cost effective, and suitable for monitoring of untreated ground water common to some small water systems and private water supplies.     

Comparison of microporous filters for concentration of viruses from wastewater.

The 1-MDS Virosorb filter and the 50S and 30S Zeta-plus filters, all with a net positive charge, were compared with the negatively charged Filterite filter for concentration of naturally occurring coliphages and animal viruses from sewage effluent. When Filterite filters were used, the effluent was adjusted to pH 3.5 and AlCl3 was added before filtration to facilitate virus adsorption. No adjustment was required with the positively charged filters. Sets of each filter type were eluted with 3% beef extract (pH 9.5) or eluted with 0.05 M glycine (pH 11.5). A maximum volume of 19 liters could be passed through 142-mm diameter Filterite filters before clogging, whereas only 11, 11, and 15 liters could be passed through the 1-MDS, 50S, and 30S filters, respectively. For equal volumes passed through the filters, coliphage recoveries were 14, 15, 18, and 37% in primary effluent and 40, 97, 50, and 46% in secondary effluent for the Filterite , 1-MDS, 50S, and 30S filters, respectively. No statistically significant difference was observed in the recovery of animal viruses among the filters from secondary effluent, whereas in the Filterite and 50S filters, higher numbers of viruses from primary effluent were recovered than in the 1-MDS and 30S filters in two of three collections. Glycine was found to be a less-efficient eluent than beef extract in the recovery of naturally occurring viruses.     

Protein synthesis in rat lung. Measurements in vivo based on leucyl-tRNA and rapidly turning-over procollagen I.

The relationships of the specific radioactivities of leucine in serum, leucine acylated to tRNA and leucine in procollagen I, procollagen III and total protein in lungs of unanaesthetized young male rats in vivo were assessed as a function of time during constant intravenous infusion of radiolabelled leucine. The specific radioactivity of free leucine in plasma reached a steady-state plateau value within 30 min of initiation of [3H]leucine infusion. Leucine acylated to tRNA isolated from lungs had the same specific radioactivity as free serum leucine. Leucine in procollagen I rapidly achieved a specific radioactivity equal to that of serum leucine and leucyl-tRNA, indicating that serum leucine and leucyl-tRNA isolated from total lung were in rapid equilibrium with the precursor leucine pool for procollagen I synthesis. On the basis of leucyl-tRNA or free serum leucine as the precursor, half-times of fractional conversion of procollagen I and III were calculated as 9 and 38 min respectively. The incorporation of leucine into mixed lung proteins calculated from the tracer studies was 6.8 mumol/day for the first 30 min of the infusion, after which the calculated rate increased to 15.0 mumol/day. This apparent increase correlated with the appearance of rapidly labelled plasma proteins trapped in the lungs. On the basis of short infusions lasting 30 min or less, followed by vascular perfusion of the lung, the average fractional synthesis rate of mixed pulmonary proteins in young male rats was 20%/day.     

Attack and defensive behaviour in the albino rat

Attack of dominant colony males of an albino rat (Rattus norvegicus) strain, on introduced strangers, produced a non-random distribution of bites, with ventral trunk virtually never bitten. Also, vibrissae-contact of attacker and defender interfered with bites to the defender's head and upper back. The specific agonistic reactions of attacking and defending rats appeared to involve strategies based on these limitation on attack: defenders utilized 'boxing' and lying 'on-the-back' behaviour, which interposed ventral trunk and vibrissae between attacker and defender. In turn, the 'lateral display' permitted attackers to circumvent the defender's behaviour. Limitations on attack therefore appeared to underlie the specific agonistic behaviour of both attacking and defending rats.     

An ultramicro method of amino acid analysis: application to studies of protein metabolism in cultured cells.

Analysis of the quantity and specific radioactivity of amino acids derived from intra-cellular pools, aminoacyl-transfer RNA, and protein hydrolysates of cultured cells has been achieved using a radiolabeled amino group ligand, dansyl chloride. Speeific activities of ¹⁴C- or ³H-labeled amino acids are calculated after reaction with appropriately labeled dansyl chloride of known specific activity. The quantity of amino acid is determined as a function of its diluting influence on a radioactive standard. The specific activity of as little as 2 pmol of amino acid can be measured using [¹⁴C]dansyl chloride the less sensitive of the two isotopic species available. Thus, cells from a single 60-mm culture dish provide sufficient material for analysis of both intracellular and transfer RNA amino acid pools, and one can easily analyze the amino acids in hydrolysates made from individual bands in polyacrylamide gels. The method offers significant improvement in speed, sensitivity, and economy over conventional methods of amino acid analysis and, because of its double-label design, gives accurate results with a minimum of technical expertise and no major equipment other than a scintillation counter.     

Effect of light nitrogenase function and synthesis in Rhodopseudomonas capsulata.

The metabolic versatility of the purple nonsulfur photosynethetic bacterial permits the expression of either a phototrophic or a dark aerobic mode of growth. These organism also possess nitrogenase activity which may function under semiaerboic conditions. On the basis of these important properties, the light dependence of nitrogenase function and synthesis in Rhodopseudomonas capsulata was investigated. Nitrogenase activity was strictly dependent on light; no activity was observed in the dark, even when energy (ATP) was supplied by oxidative phosphorylation. It was concluded that the low-potential reducing agent required by the nitrogenase-catalyzed reaction could only be generated by a photochemical reaction. Nitrogenase biosynthesis was also largely dependent on light; however, a small amount of synthesis was observed in resting cells incubated in the dark. Resting cells prepared from dark-grown cultures synthesized nitrogenase at high rates upon illumination. The highest stability of nitrogenase in these resting cells was observed when suspensions were exposed to a diurnal pattern of illumination rather than continuous light. Although nitrogenase function and synthesis are closely coupled to photosynthetic activity, the biosyntheses of bacteriochorophyll and nitrogenase are independent of each other and are most probably subject to different regulatory mechanisms by light.