, 2008; Kabashi et al., 2008b; Sreedharan et al., 2008; Yokoseki et al., 2008). TDP-43 is a widely-expressed 414-amino-acid protein encoded by the TARDBP gene on chromosome 1 (Pesiridis et al., 2009; Geser et al., 2010). It has two RNA-binding domains and a glycine-rich domain in the C-terminal part, with which it binds
to various heterogenous nuclear nucleoproteins (hnRNPs). It is more abundantly present in the nucleus than in the cytoplasm. The exact role of TDP-43 is incompletely understood, but it is thought to play a role in a variety of processes such as processing, stabilisation and transport of RNA (Buratti & Baralle, 2009; Geser et al., 2010). A well known example is its role in the splicing of cystic fibrosis transmembranous conductance regulator mRNA (Buratti selleck chemicals et al., 2001). Of interest is the finding that another target for the find more action of TDP-43 in mRNA processing is the protein SMN, deficiency of which results in spinomuscular atrophy, an infantile or juvenile onset motor neuron disorder (Burghes & Beattie, 2009). Overexpression of TDP-43 enhances exon 7 inclusion during SMN splicing, a crucial event in yielding fully active SMN protein (Bose et al., 2008). SMN deficiency in its turn is thought to cause spinomuscular atrophy through defective RNA processing or
transport (Burghes & Beattie, 2009). The possible link between SMN and TDP-43 is of major interest when thinking of a common pathway for motor neuron degeneration. The more than 25 mutations found in the TARDBP gene are, primarily, missense mutations and are almost exclusively located in the C-terminal (glycine-rich) part of the protein (Lagier-Tourenne & Cleveland, 2009). There is also a truncating mutation in this gene (Daoud et al., 2009). TARDBP mutations are rare: they probably account for < 5% of familial ALS, i.e. < 1% Tyrosine-protein kinase BLK of all ALS (Ticozzi et al., 2009a). The major interest in them comes from the finding mentioned above, that wildtype TDP-43 containing inclusions are found in the majority of sporadic
ALS patients (Neumann et al., 2006; Fig. 3). Here, we will refer to this abnormal form of TDP-43 as TDP-43SALS/FTLD in contrast to ‘normal’ TDP-43, reminiscent of the naming in prion disease, where PrPC refers to the normal PrP and PrPSc refers to the pathogenic form of PrP in sporadic and infectious Creutzfeldt–Jakob disease; it does not differ from normal PrPC in its amino acid sequence. Mutant TDP-43 refers to the mutant proteins causing the hereditary forms of ALS, just as with mutant PrP and Creutzfeldt–Jakob disease, and will be referred to as TDP-43mutant. An overwhelming number of papers on the role of TDP-43 in neurodegeneration have been published over the last 2 years. A common finding seems to be that TDP-43mutant and TDP-43SALS/FTLD are mislocated, hyperphosphorylated, abnormally processed and ubiquitinated.