Grem1 is upregulated during limb bud regeneration in Xenopus.
Ectopic grem1 does not prevent regeneration but affects the re-development phase.
Ectopic grem1 causes developing limbs to bifurcate along the proximodistal axis.
Grem1 induced limb duplications have normal symmetry.
The anteroposterior pattern of the original limb bud is inverted, and shh expanded.