Characterization of the porcine TOR1A gene: The first step towards generation of a pig model for dystonia

The TOR1A (also named DYT1) gene encodes a protein, TorsinA, a member of the AAA+ superfamily of ATPases. The AAA+ proteins have diverse functions such as organelle biogenesis, proteosome function, chaperone function, membrane trafficking and microtubule regulation. However, the molecular function of TorsinA is still largely unknown. Mutations in the TOR1A gene, primarily a 3-bp (GAG) deletion are associated with early-onset autosomal dominant torsion dystonia. Animal models may help to provide information about the underlying cellular and molecular mechanism of early-onset generalized dystonia. The close anatomical, physiological, genetic and biochemical resemblance between man and pig suggest that this animal may constitute an excellent model for this disease. This work reports the cloning and analysis of the porcine (Sus scrofa) homologue of TOR1A. Two porcine TOR1A cDNAs were amplified by reverse transcriptase polymerase chain reaction (RT-PCR), using oligonucleotide primers derived from in silico sequences. The porcine TOR1A cDNAs both encode a protein of 333 amino acids which shows a very high similarity to human (92%) TorsinA. Protein structure comparison of human and porcine TorsinA sequences revealed that there were few differences in the amino acid sequences between the two species and these are not likely to alter TorsinA structure and function. Quantitative real-time RT-PCR detection exhibited TOR1A mRNA expression in all analyzed porcine tissues, although at different levels. The TOR1A gene was demonstrated to be localized on porcine chromosome 1. Single nucleotide polymorphism (SNP) analysis revealed several SNPs in the porcine TOR1A gene, both in the coding region and also in the 3' UTR region. Overexpression of mutant (Delta E303-304) porcine TorsinA in neuroblastoma cells leads to a more perinuclear localization compared with a cytoplasmatic localization for wildtype TorsinA. Furthermore, inclusion-like structures were observed. In conclusion, the results obtained for porcine TOR1A suggest that the pig could be an ideal model for early-onset generalized dystonia. (C) 2008 Elsevier B.V. All rights reserved.