Modeling uniquely human gene regulatory function via targeted humanization of the mouse genome

Abstract

AbstractThe evolution of uniquely human traits likely entailed changes in developmental gene regulation. Human Accelerated Regions (HARs), which include transcriptional enhancers harboring a significant excess of human-specific sequence changes, are leading candidates for driving gene regulatory modifications in human development. However, insight into whether HARs alter the level, distribution, and timing of endogenous gene expression remains limited. We examined the role of the HARHACNS1(HAR2) in human evolution by interrogating its molecular functions in a genetically humanized mouse model. We find thatHACNS1maintains its human-specific enhancer activity in the mouse embryo and modifies expression ofGbx2, which encodes a transcription factor, during limb development. Using single-cell RNA-sequencing, we demonstrate thatGbx2is upregulated in the limb chondrogenic mesenchyme ofHACNS1homozygous embryos, supporting thatHACNS1alters gene expression in cell types involved in skeletal patterning. Our findings illustrate that humanized mouse models provide mechanistic insight into how HARs modified gene expression in human evolution.