Accounting for cis-regulatory constraint prioritizes genes likely to affect species-specific traits

Measuring allele-specific expression in interspecies hybrids is a powerful way to detect cis-regulatory changes underlying adaptation. However, it remains difficult to identify genes most likely to explain species-specific traits. Here, we outline a simple strategy that leverages population-scale allele-specific RNA-seq data to identify genes that have constrained cis - regulation within species yet show divergence between species. Applying this strategy to data from human-chimpanzee hybrid cortical spheroids, we identify signatures of lineage-specific selection on genes related to cellular proliferation, speech, and glucose metabolism. We also highlight cis-regulatory divergence in CUX1 and EDNRB that may shape the unique trajectory of human brain development.