Microsatellite-containing genes from the channel catfish brain: Evidence of trinucleotide repeat expansion in the coding region of nucleotide excision repair gene RAD23B

Expansion of trinucleotide repeats within genes is well known to cause path ological conditions in humans. Here we report a large number of genes conta ining simple sequence repeats (SSR) from the brain of channel catfish, of w hich a homologue of the RAD23B gene was found to include (CCA) trinucleotid e repeats within its coding region. Because of the importance of the RAD23B gene in the nucleotide excision repair (NER) system, the catfish RAD23B lo cus was further characterized. The (ACC) repeats encode a polythreonine (T) tract within the catfish RAD23B gene that is absent from the previously cl oned human and mouse genes. A survey of the allele variation at the locus i ndicated the existence of variable microsatellite repeats in the NER RAD23B gene, suggesting that the trinucleotide repeats are expanding or shrinking . The majority of individuals harbor 10 (ACC) repeats within the RAD23B gen e, but alleles with 8 and 11 repeats were also detected. The (ACC) repeats are limited to only channel catfish and the closely related blue catfish, b ut are absent from flathead catfish and the cloned human and mouse genes, s uggesting that the microsatellite invasion into the RAD23B gene is a recent event in evolution. (C) 2001 Elsevier Science.