Manganese superoxide dismutase (SOD2) converts superoxide to oxygen plus hydrogen peroxide and serves as the primary defense against mitochondrial superoxide. Impaired SOD2 activity in humans has been associated with several chronic diseases, including ovarian cancer and type I diabetes, and SOD2 overexpression appears to suppress malignancy in cultured cells. We have produced a line of SOD2 knockout mice (SOD2m1BCM/SOD2m1BcM) that survive up to 3 weeks of age and exhibit several novel pathologic phenotypes including severe anemia, degeneration of neurons in the basal ganglia and brainstem, and progressive motor disturbances characterized by weakness, rapid fatigue, and circling behavior. In addition, SOD2m1BCM/SOD2m1BCM mice older than 7 days exhibit extensive mitochondrial injury within degenerating neurons and cardiac myocytes. Approximately 10% of SOD2m1BCM/SOD2m1BCM mice exhibit markedly enlarged and dilated hearts. These observations indicate that SOD2 deficiency causes increased susceptibility to oxidative mitochondrial injury in central nervous system neurons, cardiac myocytes, and other metabolically active tissues after postnatal exposure to ambient oxygen concentrations. Our SOD2-deficient mice differ from a recently described model in which homozygotes die within the first 5 days of life with severe cardiomyopathy and do not exhibit motor disturbances, central nervous system injury, or ultrastructural evidence of mitochondrial injury.Superoxide radicals produced as by-products of metabolic oxidation can cause extensive cellular injury, and several different superoxide dismutases (SODs) have evolved to inactivate both intracellular and extracellular superoxide (1-7). Two closely related SODs containing either manganese or iron as cofactors are produced in most bacterial species, whereas most eukaryotic species contain at least two different intracellular SODs: (i) manganese superoxide (Mn SOD/SOD2) localized within the mitochondrial matrix and (ii) copper-and zinc-containing SOD1 (Cu/Zn SOD1/SOD1) localized predominantly in cytoplasmic and nuclear compartments (8).Another copper-and zinc-containing SOD found predominantly in extracellular compartments (EC SOD/SOD3) has recently been described (9). Although Mn SOD is located within the mitochondrial matrix, the SOD2 gene encoding Mn SOD is located within nuclear chromosomal DNA (10).Yeast and bacterial mutants devoid of all SOD activities exhibit hypersensitivity to oxygen and redox compounds such as paraquat, and they survive ambient oxygen by using predominantly anaerobic metabolic pathways to minimize superoxide production (2, 11-13). SODl-deficient mutants of Drosophila melanogaster are viable, but exhibit oxygen and paraquat sensitivity, decreased lifespan, and female infertility (14). Although other potent antioxidants such as glutathione, ascorbate, and tocopherols are present to varying degrees within eukaryotic and prokaryotic cells, none of these inactivates superoxide as rapidly or effectively as SODs.Several recent studies have sugg...

Single-nucleotide changes are the most common cause of natural genetic variation among members of the same species, but there is remarkably little information bearing on how they alter bacterial virulence. We recently discovered a single-nucleotide mutation in the group A Streptococcus genome that is epidemiologically associated with decreased human necrotizing fasciitis ("flesh-eating disease"). Working from this clinical observation, we find that wild-type mtsR function is required for group A Streptococcus to cause necrotizing fasciitis in mice and nonhuman primates. Expression microarray analysis revealed that mtsR inactivation results in overexpression of PrsA, a chaperonin involved in posttranslational maturation of SpeB, an extracellular cysteine protease. Isogenic mutant strains that overexpress prsA or lack speB had decreased secreted protease activity in vivo and recapitulated the necrotizing fasciitis-negative phenotype of the ΔmtsR mutant strain in mice and monkeys. mtsR inactivation results in increased PrsA expression, which in turn causes decreased SpeB secreted protease activity and reduced necrotizing fasciitis capacity. Thus, a naturally occurring single-nucleotide mutation dramatically alters virulence by dysregulating a multiple gene virulence axis. Our discovery has broad implications for the confluence of population genomics and molecular pathogenesis research.group A streptococcus | invasive infection | molecular epidemiology of strain genotype patient phenotype relationships | nonhuman primate S ingle-nucleotide mutations are the most abundant cause of genetic variation among members of the same species (1, 2). However, in striking contrast to humans, who have been studied extensively, our understanding of how naturally occurring singlenucleotide mutations alter bacterial phenotypes is rudimentary. Most prokaryotic pathogenesis research efforts have focused intensively on large regions of genetic difference, such as pathogenicity islands and prophages. Thus, there is little information that directly bears on the relationship between particular singlenucleotide changes, their direct or indirect effect on virulence factor expression, and the manifestation of medically important traits such as strain virulence and infection specificity.Recently, we have investigated the molecular genomic landscape of infection phenotype-strain genotype relationships in human patients at the nucleotide level in group A Streptococcus (GAS), a bacterial pathogen that is a major cause of human morbidity and mortality worldwide (1, 3-5). These studies were made possible by the availability of the 1.9-Mb genome sequences of 12 GAS strains cultured from patients with welldefined clinical syndromes such as pharyngitis, acute rheumatic fever, and necrotizing fasciitis (also known as "flesh-eating" disease) (1, 5). The core genome of strains of distinct M protein serotype differed, on average, by 14,475 SNPs (1, 3). In contrast, strains with the same M protein serotype were far less variable, differing overall by less...

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We have generated mice with a null mutation at the Ada locus, which encodes the purine catabolic enzyme adenosine deaminase (ADA, EC 3.5.4.4

The mitotic spindle of many mammalian cells undergoes an abrupt elongation at anaphase . In both cultured rat kangaroo (strain PtK1 ) and Chinese hamster (strain Don-C) fibroblasts, the distance from pole to pole at metaphase doubles during anaphase and telophase . In order to determine the organization and distribution of spindle microtubules during the elongation process, cells were fixed and flat embedded in Epon 812 . Selected cells were photographed with the phase-contrast microscope and then serially sectioned perpendicular to the major spindle axis . Microtubule profiles were counted in selected sections, and the number was plotted with respect to position along the spindle axis . Interpretation of the distribution profiles indicated that not all interpolar microtubules extended from pole to pole . It is estimated that 55-70 0/0 of the interpolar microtubules are overlapped at the cell equator while 30-45% extend across the equator into both half spindles . This arrangement appeared to persist from early anaphase (before elongation) until telophase after the elongation process . Although sliding or shearing of microtubules may occur in the spindle, such appears not to be the mechanism by which the spindle elongates in anaphase . Instead, our data support the hypothesis that spindle elongation occurs by growth of prepositioned microtubules which "push" the poles apart .