Pathogenicity in Francisella tularensis subspecies

.Sequencing of the non-pathogenic Francisella tularensis sub-species novicida U112, and comparison with two pathogenic sub-species, provides insights into the evolution of pathogenicity in these species.

Wolf-Hirschhorn syndrome (WHS) is a multiple malformation syndrome characterised by mental and developmental defects resulting from the absence of a segment of one chromosome 4 short arm (4p16.3). Due to the complex and variable expression of this disorder, it is thought that the WHS is a contiguous gene syndrome with an undefined number of genes contributing to the phenotype. In an effort to identify genes that contribute to human development and whose absence results in this syndrome, we have utilised a series of landmark cosmids to characterise a collection of WHS patient derived cell lines. Fluorescence in situ hybridisation with these cosmids was used to refine the WHS critical region (WHSCR) to 260 kb. The genomic sequence of this region is available and analysis of this sequence through BLAST detected several cDNA clones in the dbEST data base. A total of nine independent cDNAs, and their predicted translation products, from this analysis show no significant similarity to members of DNA or protein databases. Furthermore, these genes have been localised within the WHS critical region and reveal an interesting pattern of transcriptional organisation. A previously published report of a patient with proximal 4p- syndrome further refines the WHSCR to 165 kb defined by the loci D4S166 and D4S3327. This work provides the starting point to understand how multiple genes or other mechanisms can contribute to the complex phenotype associated with the Wolf-Hirschhorn syndrome.

The absence of dystrophin in Duchenne muscular dystrophy (DMD) leads to sarcolemmal instability and enhances the susceptibility of muscle fibers to contraction-induced injury. Various viral vectors have been used to deliver mini- and microdystrophin expression cassettes to muscles of dystrophin-deficient mdx mice, significantly increasing both the morphological and the functional properties of the muscles. However, dystrophin delivery to adult mdx mice has not yielded a complete rescue of the dystrophic phenotype. Here we investigated a novel strategy involving dual gene transfer of recombinant adeno-associated viral vectors expressing either microdystrophin (rAAV-muDys) or a muscle-specific isoform of Igf-1 (rAAV-mIgf-1). Injection of mdx muscles with rAAV-muDys reduced myofiber degeneration and turnover and increased their resistance to mechanical injury, but did not increase muscle mass or force generation. Injection of mdx muscles with rAAV-mIgf-1 led to increased muscle mass, but did not provide protection against mechanical injury or halt myofiber degeneration, leading to loss of the vector over time. In contrast, co-injection of the rAAV-muDys and rAAV-mIgf-1 vectors resulted in increased muscle mass and strength, reduced myofiber degeneration, and increased protection against contraction-induced injury. These results suggest that a dual-gene, combinatorial strategy could enhance the efficacy of gene therapy of DMD.

Duchenne muscular dystrophy is an X-linked recessive disorder, primarily characterized by progressive muscle weakness and wasting. The disease results from the absence of dystrophin, however the precise molecular mechanisms leading to muscle pathology are poorly understood. Dystrophic muscles undergo increased oxidative stress and altered calcium homeostasis, which may contribute to myofiber loss by triggering both necrosis and apoptosis. Recent studies have identified ARC (apoptosis repressor with caspase recruitment domain) as an abundant protein in human muscle that can inhibit both hypoxia and caspase-8-induced apoptosis as well as protect cells from oxidative stress. To explore a potential role for ARC in protecting muscle fibers from dystrophic breakdown, we have cloned and characterized murine ARC and studied its expression in normal and dystrophic mouse muscle. ARC is expressed at high levels in striated muscle and displays fiber-type restricted expression patterns. ARC expression levels are normal in dystrophic mdx mice, although the intracellular localization pattern of ARC is slightly altered compared with normal muscles. Overexpression of ARC in transgenic mdx mice failed to alleviate the dystrophic pathology in skeletal muscles, suggesting that misregulation of the molecular pathways regulated by ARC does not significantly contribute to myofiber death.

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