Adaptive sequence divergence forged new neurodevelopmental enhancers in humans

Area of Science:

• Genomics
• Human Evolution
• Neuroscience

Background:

• Human-specific traits are often studied in conserved genomic regions.
• This approach overlooks functional elements evolving from previously neutral regions.
• Understanding rapid genomic evolution is key to human uniqueness.

Purpose of the Study:

• To identify and characterize rapidly evolved genomic regions in the human lineage.
• To investigate the functional significance of these regions in human development and disease.
• To explore the evolutionary dynamics of human-specific genomic elements.

Main Methods:

• Analysis of human genome sequences to identify rapidly evolved regions (termed HAQERs).
• Investigation of chromatin states and association with disease-related genetic variants.
• Utilizing a multiplex, single-cell in vivo enhancer assay to assess enhancer activity.

Main Results:

• Identified human ancestor quickly evolved regions (HAQERs) that underwent rapid, episodic positive selection before the human-Neanderthal split.
• HAQERs show enrichment for bivalent chromatin states in neurodevelopmental and gastrointestinal tissues.
• Discovered hominin-unique enhancers within HAQERs in the developing cerebral cortex.
• Found genetic variants linked to neurodevelopmental diseases within HAQERs.

Conclusions:

• HAQERs represent a distinct class of rapidly adapted genomic regions in human evolution.
• These regions played a role in generating unique human enhancers, particularly in the brain.
• Lack of pleiotropic constraints and high mutation rates facilitated HAQER adaptation, potentially increasing disease susceptibility.