chr2 · 2q14.2 · 546 nt · 2008

HACNS1

HAR2

What it is

HACNS1 is a conserved noncoding enhancer that gained 16 human-specific letter changes. In reporter experiments it drives strong activity in the developing limb and hand. The nearby protein genes themselves are not rewritten — the schedule and location of their use is.

Why it matters

Classic limb enhancer; experimental reporter validation.

Operator load

• 01 · ΔE

  Enhancer activity

  These stretches of DNA do not code for proteins. They act as volume knobs — turning nearby brain-development genes up or down at the right moment.

• 03 · T

  Three-dimensional rewiring

  The genome folds in 3D. Human-specific changes can re-route which switches sit next to which genes, even if the letters look similar in a straight line.

• 04 · D

  Copy-number expansion

  Sometimes the switch is duplicated. Extra copies give evolution more material to experiment with — one copy keeps the old job, another can specialize.

Prabhakar et al. Science 2008