Pleiotropic effects of trans-regulatory mutations on fitness and gene expression.

Variation in gene expression arises from cis- and trans-regulatory mutations, which contribute differentially to expression divergence. We compare the impacts on gene expression and fitness resulting from cis- and trans-regulatory mutations in , with a focus on the gene. We use the effects of cis-regulatory mutations to infer effects of trans-regulatory mutations attributable to impacts beyond the focal gene, revealing a distribution of pleiotropic effects. Cis- and trans-regulatory mutations had different effects on gene expression with pleiotropic effects of trans-regulatory mutants affecting expression of genes both in parallel to and downstream of the focal gene. The more widespread and deleterious effects of trans-regulatory mutations we observed are consistent with their decreasing relative contribution to expression differences over evolutionary time.