Showing papers by "Kay E. Davies published in 2006"

Molecular mechanisms of muscular dystrophies: old and new players

Abstract: The study of the muscle cell in the muscular dystrophies (MDs) has shown that mutant proteins result in perturbations of many cellular components. MDs have been associated with mutations in structural proteins, signalling molecules and enzymes as well as mutations that result in aberrant processing of mRNA or alterations in post-translational modifications of proteins. These findings have not only revealed important insights for cell biologists, but have also provided unexpected and exciting new approaches for therapy.

Functional genetic analysis of mutations implicated in a human speech and language disorder

Abstract: Mutations in the FOXP2 gene cause a severe communication disorder involving speech deficits (developmental verbal dyspraxia), accompanied by wide-ranging impairments in expressive and receptive language. The protein encoded by FOXP2 belongs to a divergent subgroup of forkhead-box transcription factors, with a distinctive DNA-binding domain and motifs that mediate hetero- and homodimerization. Here we report the first direct functional genetic investigation of missense and nonsense mutations in FOXP2 using human cell-lines, including a well-established neuronal model system. We focused on three unusual FOXP2 coding variants, uniquely identified in cases of verbal dyspraxia, assessing expression, subcellular localization, DNA-binding and transactivation properties. Analysis of the R553H forkhead-box substitution, found in all affected members of a large three-generation family, indicated that it severely affects FOXP2 function, chiefly by disrupting nuclear localization and DNA-binding properties. The R328X truncation mutation, segregating with speech/language disorder in a second family, yields an unstable, predominantly cytoplasmic product that lacks transactivation capacity. A third coding variant (Q17L) observed in a single affected child did not have any detectable functional effect in the present study. In addition, we used the same systems to explore the properties of different isoforms of FOXP2, resulting from alternative splicing in human brain. Notably, one such isoform, FOXP2.10+, contains dimerization domains, but no DNA-binding domain, and displayed increased cytoplasmic localization, coupled with aggresome formation. We hypothesize that expression of alternative isoforms of FOXP2 may provide mechanisms for post-translational regulation of transcription factor function.

A mutation in the small heat-shock protein HSPB1 leading to distal hereditary motor neuronopathy disrupts neurofilament assembly and the axonal transport of specific cellular cargoes

Abstract: Distal hereditary motor neuronopathies (dHMNs) are a clinically and genetically heterogeneous group of disorders in which motor neurons selectively undergo age-dependant degeneration. Mutations in the small heat-shock protein HSPB1 (HSP27) are responsible for one form of dHMN. In this study, we have analysed the effect of expressing a form of mutant HSPB1 in primary neuronal cells in culture. Mutant (P182L) but not wild-type HSPB1 led to the formation of insoluble intracellular aggregates and to the sequestration in the cytoplasm of selective cellular components, including neurofilament middle chain subunit (NF-M) and p150 dynactin. These findings suggest a possible pathogenic mechanism for HSPB1 whereby the mutation may lead to preferential motor neuron loss by disrupting selective components essential for axonal structure and transport.

Expansion of revertant fibers in dystrophic mdx muscles reflects activity of muscle precursor cells and serves as an index of muscle regeneration

Abstract: Duchenne muscular dystrophy and the mdx mouse myopathies reflect a lack of dystrophin in muscles. However, both contain sporadic clusters of revertant fibers (RFs) that express dystrophin. RF clusters expand in size with age in mdx mice. To test the hypothesis that the expansion of clusters is achieved through the process of muscle degeneration and regeneration, we analyzed muscles of mdx mice in which degeneration and regeneration were inhibited by the expression of micro-dystrophins or utrophin transgenes. Postnatal RF expansion was diminished in direct correlation to the protective effect of the transgene expression. Similarly, expansion of RFs was inhibited when muscle regeneration was blocked by irradiation. However, in irradiated muscles, irradiation-tolerant quiescent muscle precursor cells reactivated by notexin effectively restored RF expansion. Our observations demonstrate that revertant events occur initially within a subset of muscle precursor cells. The proliferation of these cells, as part of the regeneration process, leads to the expansion of RF clusters within degenerating muscles. This expansion of revertant clusters depicts the cumulative history of regeneration, thus providing a useful index for functional evaluation of therapies that counteract muscle degeneration.

MLP accumulation and remodelling in the infarcted rat heart.

Abstract: Mutation of cytoskeletal protein genes results in abnormal protein function and causes cardiomyopathy. We hypothesised that cardiac levels of cytoskeletal proteins, such as dystrophin, desmin and muscle LIM protein (MLP), would be altered during remodelling caused by myocardial infarction (MI). We measured left-ventricular morphology, function and cytoskeletal protein levels 10 weeks after coronary artery ligation or sham operation in male Wistar rats. Two-dimensional echocardiography revealed significant impairment of systolic function and decreased ejection fraction in infarcted hearts compared with sham (47+/-5% versus 73+/-4%), commensurate with the development of heart failure. Western blotting was used to measure levels of beta-myosin heavy chain (beta-MyHC), a marker of hypertrophy, and levels of dystrophin, desmin, MLP, beta-tubulin, utrophin and syncoilin, using GAPDH for normalization. Relative to shams, beta-MyHC and MLP levels were increased 1.9-fold and 1.7-fold, respectively, in infarcted rat hearts, whereas the levels of other cytoskeletal proteins were unchanged. Both MLP and desmin protein levels correlated negatively with ejection fraction, with the strongest relation between MLP and ejection fraction (r=-0.95, n=13, p<0.0001). This work suggests that MLP may play an important compensatory role in cardiac remodelling following MI.

SI10 Effects of Hypoxia on the Proliferation and Differentiation Potential of Human Cord Blood‐ and Bone Marrow‐Derived Stem/Progenitor Cells

Abstract: Umbilical cord blood (UCB) and bone marrow (BM)-derived stem and progenitor cells possess two characteristics required for successful tissue regeneration, which are extensive proliferative capacity and the ability to differentiate into multiple cell lineages. Within the normal BM and in pathological conditions, areas of hypoxia may have a role in maintaining stem cell fate or determining the fine equilibrium between their proliferation and differentiation. In this study, the transcriptional profiles, proliferation and differentiation potential of UCB CD133+ cells and BM mesenchymal cells (BMMC) exposed to normoxia and hypoxia were analysed and compared. Both progenitor cell populations responded to hypoxic stimuli by stabilising the HIF1-α protein. Short exposures to hypoxia increased the clonogenic myeloid capacity of UCB CD133+ cells and resulted in a significant increase in BMMC number. The differentiation potential of BMMC and UCB CD133+ cells was unaltered by hypoxia with the lineages tested. When their transcriptional profiles were compared, 183 genes in UCB CD133+ cells and 45 genes in BMMC were differentially regulated by hypoxia. These genes included known hypoxia-responsive targets such as BNIP3, PGK1, ENO2 and VEGF, and other genes not previously described to be regulated by hypoxia. Several of these genes, namely CDTSPL, CCL20, LSP1,NEDD9, TMEM45A, EDG-1 and EPHA3 were confirmed to be regulated by hypoxia using quantitative RT-PCR. These results therefore provide a global view of the signalling and regulatory network that controls oxygen sensing in human adult stem/progenitor cells derived from haematopoietic tissues.