Depending on the relative expression of the various

transcripts, the loss of C9ORF72 transcript 1 may have a significant impact on selleck compound selective tissues or cell types. Although preliminary analyses of C9ORF72 protein levels in cultured cells and whole brain tissue homogenate did not show an obvious change in the steady-state levels, we cannot exclude the possibility that reduced transcript levels of C9ORF72 affect protein translation under conditions of stress or may affect protein turnover and/or function. We also cannot guarantee the specificity of the commercial C9ORF72 antibodies used in this study since careful characterization of these antibodies has not yet been performed. In future experiments it will be crucial to generate more specific C9ORF72 antibodies and develop more quantitative approaches to measure Epigenetics inhibitor C9ORF72 levels to further clarify the expression and localization of each of the C9ORF72 isoforms in different tissues and at various stages of disease progression. Although speculative at this time, it is possible that the expression pattern of C9ORF72 in individual patients may contribute to the variability in disease phenotype (FTD versus ALS) or course. A common feature of non-coding

repeat expansion disorders which has gained increased attention in recent years is the accumulation of RNA fragments composed of the repeated nucleotides as RNA foci in the nucleus and/or cytoplasm of affected cells (Todd and Paulson, 2010). In several disorders, the RNA foci have been shown to sequester RNA-binding

proteins, leading to dysregulation of alternative mRNA splicing (Miller Isotretinoin et al., 2000, Sofola et al., 2007, Timchenko et al., 1996 and White et al., 2010). Using an oligonucleotide probe specific for the GGGGCC repeat we confirmed the presence of such nuclear RNA foci in postmortem cerebral cortex and spinal cord tissue of C9ORF72 expanded repeat carriers. The GGGGCC sequence motif predicts the potential binding of several RNA-binding proteins, including the serine/arginine-rich splicing factor 1 (SRSF1) and the heterozygous nuclear ribonucleoprotein (hnRNP) A2/B1 ( Cartegni et al., 2003, Smith et al., 2006 and Sofola et al., 2007). Although future studies are needed to clarify whether these or other RNA-binding proteins play any role in disease pathogenesis, aberrant RNA splicing is a highly plausible mechanism in chromosome 9p-linked FTD/ALS given the accumulating evidence for RNA misprocessing in the pathogenesis of both ALS and FTD ( Bäumer et al., 2010). Dysregulation of hnRNP A2/B1 is a particularly interesting possibility since this protein is known to interact with the C/G-rich repeats that form RNA foci in another neurodegenerative condition (FXTAS) and because hnRNP A2/B1 has been shown to interact directly with TDP-43 ( Buratti et al., 2005 and Sofola et al., 2007).