Maximilian Oliver Press | bioRxiv Science

bioRxiv2016

The variable ELF3 polyglutamine tract mediates complex epistatic interactions in Arabidopsis thaliana.

Short tandem repeats are hypervariable genetic elements that occur frequently in coding regions. Their high mutation rate readily generates genetic variation contributing to adaptive evolution and human diseases. We recently proposed that short tandem repeats are likely to engage in epistasis because they are well-positioned to compensate for genetic variation arising at other loci due to their high mutation rate. We previously reported that natural ELF3 polyglutamine variants cause reciprocal genetic incompatibilities in two divergent Arabidopsis thaliana backgrounds. Here, we dissected the genetic architecture of this incompatibility and used a yeast two-hybrid strategy to identify proteins whose physical interactions with ELF3 were modulated by polyglutamine tract length. Using these two orthogonal approaches, we identify specific genetic interactions and physical mechanisms by which the ELF3 polyglutamine tract may mediate the observed genetic incompatibilities. Our work elucidates how short tandem repeat variation, which is generally underascertained in population-scale sequencing, can contribute to phenotypic variation. Furthermore, our results support our proposal that highly variable STR loci can contribute disproportionately to the epistatic component of heritability.

Genetics↗

bioRxiv2014

MIPSTR: a method for multiplex genotyping of germ-line and somatic STR variation across many individuals

Abstract Short tandem repeats (STRs) are highly mutable genetic elements that often reside in functional genomic regions. The cumulative evidence of genetic studies on individual STRs suggests that STR variation profoundly affects phenotype and contributes to trait heritability. Despite recent advances in sequencing technology, STR variation has remained largely inaccessible across many individuals compared to single nucleotide variation or copy number variation. STR genotyping with short-read sequence data is confounded by (1) the difficulty of uniquely mapping short, low-complexity reads and (2) the high rate of STR amplification stutter. Here, we present MIPSTR, a robust, scalable, and affordable method that addresses these challenges. MIPSTR uses targeted capture of STR loci by single-molecule Molecular Inversion Probes (smMIPs) and a unique mapping strategy. Targeted capture and mapping strategy resolve the first challenge; the use of single molecule information resolves the second challenge. Unlike previous methods, MIPSTR is capable of distinguishing technical error due to amplification stutter from somatic STR mutations. In proof-of-principle experiments, we use MIPSTR to determine germ-line STR genotypes for 102 STR loci with high accuracy across diverse populations of the plant A. thaliana. We show that putatively functional STRs may be identified by deviation from predicted STR variation and by association with quantitative phenotypes. Employing DNA mixing experiments and a mutant deficient in DNA repair, we demonstrate that MIPSTR can detect low-frequency somatic STR variants. MIPSTR is applicable to any organism with a high-quality reference genome and is scalable to genotyping many thousands of STR loci in thousands of individuals.

Genomics↗