131 Using whole-genome sequencing to search for trans-modifiers of repeat expansions

Abstract

Expansions of simple repetitive DNA sequences are responsible for a large number of human hereditary diseases. The severity and age of onset of each disorder can be estimated from the length of the inherited repeat tract; however, the subsequent expansion rate is itself a heritable trait. This points to a role for trans-acting modifier genes, whose actions may be altered by single nucleotide polymorphisms. Previously, our lab has used a yeast system to study large-scale expansions of GAA trinucleotide repeats, and a number of gene knockouts have been shown to induce expansions. While this has been highly informative, gene knockouts are a rather blunt tool, which are not suitable to approximate the spectrum of SNPs that might affect repeat expansions, as has been predicted in human populations. To address this problem, we have developed a novel, alternative screening method which employs UV mutagenesis followed by the whole-genome sequencing. This approach allowed us to detect SNPs that modified the likelihood of repeat expansions in yeast. Unexpectedly, several such SNPs appeared in a yeast gene whose product is involved in the cleavage and polyadenylation of RNA transcripts. We discuss possible mechanisms linking transcript processing with repeat instability.