Preprint: human accelerated region HACNS1 drives opposing developmental timing shifts in face and limb

A preprint posted to bioRxiv (not yet peer-reviewed) uses a genetically humanised mouse model carrying the human sequence of HACNS1 — one of the most conserved human accelerated regions (HARs), a class of genomic loci that are highly conserved across vertebrates but show a burst of substitutions on the human lineage — to investigate its role in developmental timing, a phenomenon known as heterochrony.

Using single-nucleus RNA sequencing and developmental trajectory analyses, the authors find that HACNS1 drives opposing heterochronic shifts: it accelerates development in craniofacial tissues whilst slowing it in limb tissues. HACNS1 encodes a transcriptional enhancer with human-specific activity, and this work suggests that regulatory sequence changes at this locus contributed to the reshaping of developmental schedules that distinguish humans from other primates.

The study is notable for linking a specific non-coding regulatory element to bidirectional changes in developmental timing across distinct tissue types — an unusual result that challenges simple models in which HARs exert uniform effects on human-specific traits. The findings contribute to ongoing research into the evolutionary origins of human craniofacial and limb anatomy.

As a preprint, this work has not yet been peer-reviewed.