An Engrailed1 enhancer underlies human thermoregulatory evolution

Humans rely on sweating to cool off and have the highest eccrine sweat gland density among mammals. We investigated whether altered regulation of the Engrailed 1 (EN1) gene, the levels of which are critical for patterning eccrine glands during development, could underlie the evolution of this defining human trait. First, we identify five EN1 candidate enhancers (ECEs) using comparative genomics and validation of enhancer activity in mouse skin. The human ortholog of one ECE, hECE18, contains multiple derived substitutions that together dramatically increase the activity of this enhancer in keratinocytes. Targeted repression of hECE18 reduces EN1 expression in human keratinocytes, indicating hECE18 upregulates EN1 in this context. Finally, we find that hECE18 increases ectodermal En1 in a humanized knock-in mouse to increase eccrine gland number. Our study uncovers a genetic basis for the evolution of one of the most singular human adaptations and implicates the recurrent mutation of a single enhancer as a novel mechanism for evolutionary change.