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Background: The evolutionarily ancient parasite, Trypanosoma brucei, is unusual in that the majority of its genes are regulated post-transcriptionally, leading to the suggestion that transcript abundance of most genes does not vary significantly between different life cycle stages despite the fact that the parasite undergoes substantial cellular remodelling and metabolic changes throughout its complex life cycle. To investigate this in the clinically relevant sub-species, Trypanosoma brucei gambiense, which is the causative agent of the fatal human disease African sleeping sickness, we have compared the transcriptome of two different life cycle stages, the potentially human-infective bloodstream forms with the non-human-infective procyclic stage using digital gene expression (DGE) analysis. Results: Over eleven million unique tags were generated, producing expression data for 7360 genes, covering 81% of the genes in the genome. Compared to microarray analysis of the related T. b. brucei parasite, approximately 10 times more genes with a 2.5-fold change in expression levels were detected. The transcriptome analysis revealed the existence of several differentially expressed gene clusters within the genome, indicating that contiguous genes, presumably from the same polycistronic unit, are co-regulated either at the level of transcription or transcript stability. Conclusions: DGE analysis is extremely sensitive for detecting gene expression differences, revealing firstly that a far greater number of genes are stage-regulated than had previously been identified and secondly and more importantly, this analysis has revealed the existence of several differentially expressed clusters of genes present on what appears to be the same polycistronic units, a phenomenon which had not previously been observed in microarray studies. These differentially regulated clusters of genes are in addition to the previously identified RNA polymerase I polycistronic units of variant surface glycoproteins and procyclin expression sites, which encode the major surface proteins of the parasite. This raises a number of questions regarding the function and regulation of the gene clusters that clearly warrant further study. [ABSTRACT FROM AUTHOR]

Abstract: Huntington disease (HD) is associated with an unstable trinucleotide CAG·CTG repeat expansion. Although the repeat length is inversely correlated with the age-at-onset of symptoms, variability between patients who have inherited the same HD repeat length clearly suggests that other factors influence this aspect of the disease. As repeat length profiles in somatic tissues suggest that repeat length gains may contribute to both the tissue-specificity and progressive nature of HD pathogenesis, genetic modifiers of mutation length variability may therefore influence the age-at-onset of the disease. Using a sensitive single molecule-PCR assay we show that HD mutation length profiles in buccal cell DNA vary from individual to individual. The resulting data provide the first quantitative evidence that inherited CAG·CTG repeat length has a major influence on somatic CAG·CTG repeat length variation. In addition, we confirm that further environmental and/or genetic modifiers of repeat length variation exist and discuss the implications that our results may have on understanding the factors that influence severity and age-at-onset of Huntington disease symptoms. [Copyright &y& Elsevier]