Nemaline myopathy caused by mutations in the muscle alpha-skeletal-actin gene

Nemaline myopathy (NM) is a clinically and genetically heterogeneous disorder characterized by muscle weakness and the presence of nemaline bodies (rods) in skeletal muscle. Disease-causing mutations have been reported in five genes, each encoding a protein component of the sarcomeric thin filament. Recently, we identified mutations in the muscle alpha-skeletal-actin gene (ACTA1) in a subset of patients with NM. In the present study, we evaluated a new series of 35 patients with NM. We identified five novel missense mutations in ACTA1, which suggested that mutations in muscle alpha-skeletal actin account for the disease in approximately 15% of patients with NM. The mutations appeared de novo and represent new dominant mutations. One proband subsequently had two affected children, a result consistent with autosomal dominant transmission. The seven patients exhibited marked clinical variability, ranging from severe congenital-onset weakness, with death from respiratory failure during the 1st year of life, to a mild childhood-onset myopathy, with survival into adulthood. There was marked variation in both age at onset and clinical severity in the three affected members of one family. Common pathological features included abnormal fiber type differentiation, glycogen accumulation, myofibrillar disruption, and "whorling" of actin thin filaments. The percentage of fibers with rods did not correlate with clinical severity; however, the severe, lethal phenotype was associated with both severe, generalized disorganization of sarcomeric structure and abnormal localization of sarcomeric actin. The marked variability, in clinical phenotype, among patients with different mutations in ACTA1 suggests that both the site of the mutation and the nature of the amino acid change have differential effects on thin-filament formation and protein-protein interactions. The intrafamilial variability suggests that alpha-actin genotype is not the sole determinant of phenotype.     

Histone octamer transfer by a chromatin-remodeling complex

RSC, an abundant, essential chromatin-remodeling complex related to SWI/SNF complex, catalyzes the transfer of a histone octamer from a nucleosome core particle to naked DNA. The newly formed octamer-DNA complex is identical with a nucleosome in all respects. The reaction requires ATP and involves an activated RSC-nucleosome intermediate. The mechanism may entail formation of a duplex displacement loop on the nucleosome, facilitating the entry of exogeneous DNA and the release of the endogenous molecule.     

Routes for fructose utilization by Escherichia coli

There are three main routes for the utilization of fructose by Escherichia coli. One (Route A) predominates in the growth of wild-type strains. It involves the functioning of the phosphoenolpyruvate:glycose phosphotransferase system (PTS) and a fructose operon, mapping at min. 48.7, containing genes for a membrane-spanning protein (fruA), a 1-phosphofructose kinase (fruK) and a diphosphoryl transfer protein (fruB), under negative regulation by a fruR gene mapping at min. 1.9. A second route (Route B) also involves the PTS and membrane-spanning proteins that recognize a variety of sugars possessing the 3,4,5-D-arabino-hexoseconfiguration but with primary specificity for mannose(manXYZ), mannitol (mtlA) and glucitol (gutA) and which, if over-produced, can transport also fructose. A third route (Route C), functioning in mutants devoid of Routes A and B, does not involve the PTS: fructose diffuses into the cell via an isoform (PtsG-F) of the major glucose permease of the PTS and is then phosphorylated by ATP and a manno(fructo)kinase (Mak+) specified by a normally cryptic 1032 bp ORF (yajF) of hitherto unknown function (Mak-o), mapping at min. 8.8 and corresponding to a peptide of 344 amino acids. Conversion of the Mak-o to the Mak+ phenotypeinvolves an A24D mutation in a putative regulatory region.     

FGF is an essential mitogen and chemoattractant for the air sacs of the drosophila tracheal system

The Drosophila adult has a complex tracheal system that forms during the pupal period. We have studied the derivation of part of this system, the air sacs of the dorsal thorax. During the third larval instar, air sac precursor cells bud from a tracheal branch in response to FGF, and then they proliferate and migrate to the adepithelial layer of the wing imaginal disc. In addition, FGF induces these air sac precursors to extend cytoneme-like filopodia to FGF-expressing cells. These findings provide evidence that FGF is a mitogen in Drosophila, correlate growth factor signaling with filopodial contact between signaling and responding cells, and suggest that FGF can act on differentiated tracheal cells to induce a novel behavior and role.     

An association between the acute phase response and patterns of antigen induced T cell proliferation in juvenile idiopathic arthritis

The aim of this research was to determine whether all memory T cells have the same propensity to migrate to the joint in patients with juvenile idiopathic arthritis. Paired synovial fluid and peripheral blood mononuclear cell proliferative responses to a panel of antigens were measured and the results correlated with a detailed set of laboratory and clinical data from 39 patients with juvenile idiopathic arthritis. Two distinct patterns of proliferative response were found in the majority of patients: a diverse pattern, in which synovial fluid responses were greater than peripheral blood responses for all antigens tested; and a restricted pattern, in which peripheral blood responses to some antigens were more vigorous than those in the synovial fluid compartment. The diverse pattern was generally found in patients with a high acute phase response, whereas patients without elevated acute phase proteins were more likely to demonstrate a restricted pattern. We propose that an association between the synovial fluid T cell repertoire and the acute phase response suggests that proinflammatory cytokines may influence recruitment of memory T cells to an inflammatory site, independent of their antigen specificity. Additionally, increased responses to enteric bacteria and the presence of αEβ7 T cells in synovial fluid may reflect accumulation of gut associated T cells in the synovial compartment, even in the absence of an elevated acute phase response. This is the first report of an association between the acute phase response and the T cell population recruited to an inflammatory site.