What it is
Tandem repeats are short DNA sequences repeated back to back, highly variable between people and spread across the genome. They are important regulators of gene expression but remain underexplored, because genotyping them accurately is hard. The authors generated whole-genome and single-cell RNA sequencing from more than 5.4 million blood-derived cells across 1,925 individuals in two cohorts, and combined the results to characterise how variation at more than 1.7 million tandem repeat sites affects gene expression in specific immune cell types. They identify more than 69,000 single-cell expression quantitative trait loci, associations between a repeat's length and a gene's expression, 30.7% of them specific to one of 28 immune cell types. Matched chromatin-accessibility profiles from more than 3.4 million nuclei in 922 individuals find accessibility effects for nearly a third of the expression-associated repeats. Fine-mapping implicates 1,490 repeats as candidate causal drivers of expression in 6.1% of the genes tested, and colocalization highlights more than 200 genes where repeats likely mediate genetic associations with immune and blood traits.
Why it matters
Repeated DNA stretches, usually skipped by genetic studies that read single letters, turn out to regulate immune genes cell type by cell type. Because the effects are tied to specific cell types, and the same repeats also show up as chromatin-accessibility associations, the work suggests the repeats act through cis-regulatory architecture rather than only tracking it. In the preprint, examples include a poly(T) repeat in the promoter of KIF16B whose effect in cytotoxic immune cells colocalizes with mean platelet volume, and a repeat in the coding sequence of ALMS1, specific to CD8+ naive T cells, colocalizing with haematocrit.
Underlined numbers link to their source. Every metric and quoted figure is listed under Sources and data below.
Filed underGenetic Associations and Epidemiology, Genomics and Chromatin Dynamics, Genomic variations and chromosomal abnormalities