Spontaneously epileptic rat (SER) is a homozygote for both tremor (tm) and zitter (zi) genes and exhibits epilepsy-like seizures and spongiform encephalopathy. Genetic linkage analyses revealed that the tm and zi loci were tightly linked to the synaptobrevin-2 (Syb2) on chromosome 10 and the prion protein (Prnp) on chromosome 3, respectively. The genomic DNA sequences of Syb2 of the tm/tm (TRM) rats and exon 2 of the Prnp of the zi/zi (ZI) rats were identical to those of a control rat strain WTC. In addition, no difference was detected for expression of the Syb2 and Prnp on the Northern blot analyses of TRM, ZI and WTC brain, suggesting that the Syb2 and Prnp genes are not the tm and zi, respectively. The assignments of tm and zi to rat chromosome 10q24 and 3q35, however, will be the first step towards the positional cloning of the genes.
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