Muscleblind participates in RNA toxicity of expanded CAG and CUG repeats in <Emphasis Type="Italic">Caenorhabditis elegans</Emphasis>

We have utilized Caenorhabditis elegans as a model to investigate the toxicity and underlying mechanism of untranslated CAG repeats in comparison to CUG repeats. Our results indicate that CAG repeats can be toxic at the RNA level in a length-dependent manner, similar to that of CUG repeats. Both CAG and CUG repeats of toxic length form nuclear foci and co-localize with C. elegans muscleblind (CeMBL), implying that CeMBL may play a role in repeat RNA toxicity. Consistently, the phenotypes of worms expressing toxic CAG and CUG repeats, including shortened life span and reduced motility rate, were partially reversed by CeMbl over-expression. These results provide the first experimental evidence to show that the RNA toxicity induced by expanded CAG and CUG repeats can be mediated, at least in part, through the functional alteration of muscleblind in worms.     

Phylogenetic origin of LI-cadherin revealed by protein and gene structure analysis

The intestine specific LI-cadherin differs in its overall structure from classical and desmosomal cadherins by the presence of seven instead of five cadherin repeats and a short cytoplasmic domain. Despite the low sequence similarity, a comparative protein structure analysis revealed that LI-cadherin may have originated from a five-repeat predecessor cadherin by a duplication of the first two aminoterminal repeats. To test this hypothesis, we cloned the murine LI-cadherin gene and compared its structure to that of other cadherins. The intron-exon organization, including the intron positions and phases, is perfectly conserved between repeats 3–7 of LI-cadherin and 1–5 of classical cadherins. Moreover, the genomic structure of the repeats 1–2 and 3–4 is identical for LI-cadherin and highly similar to that of the repeats 1–2 of classical cadherins. These findings strengthen our assumption that LI-cadherin originated from an ancestral cadherin with five domains by a partial gene duplication event.Received 22 December 2003; received after revision 9 February 2004; accepted 27 February 2004     

Short sequence repeats in microbial pathogenesis and evolution

Repetitive DNA is ubiquitous in microbial genomes. Different classes of short sequence repeats (SSRs) have been identified and demonstrated to be generally heterogeneous in a locus-dependent manner, reflected in variation in the number of repeat units present at a given genomic site or by sequence heterogeneity among individual units. Both types of variability can be used to assess intra-species genetic diversity. Repeat variability often affects the coding potential of the region in which the repetitive element is located. This implies that determination of the primary structure of variable numbers of tandem repeats can be used for epidemiological identification purposes, and also for the analysis of gene function. Precise assessment of SSR structure can also generate insight into the regulation of gene expression. Together, DNA repeat analysis in microbial species provides information on both functional and evolutionary aspects of genetic diversity among microbial isolates.     

Research advances in gene therapy approaches for the treatment of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease of motor neurons that causes progressive muscle weakness, paralysis, and premature death. No effective therapy is available. Research in the motor neuron field continues to grow, and recent breakthroughs have demonstrated the possibility of completely achieving rescue in animal models of spinal muscular atrophy, a genetic motor neuron disease. With adeno-associated virus (AAV) vectors, gene transfer can be achieved with systemic non-invasive injection and minimal toxicity. In the context of this success, we review gene therapy approaches for ALS, considering what has been done and the possible future directions for effective application of the latest generation of vectors for clinical translation. We focus on recent developments in the areas of RNA/antisense-mediated silencing of specific ALS causative genes like superoxide dismutase-1 and other molecular pathogenetic targets, as well as the administration of neuroprotective factors with viral vectors. We argue that gene therapy offers new opportunities to open the path for clinical progress in treating ALS.