Fig. 4.

The maintenance of limb bud symmetry. (A) Schematic of a mouse forelimb showing the pathway that promotes forelimb outgrowth. Tbx5, which is expressed symmetrically, acts as a wedge to maintain symmetry that buffers an unknown L-R influencer. Loss of Tbx5 causes left-biased forelimb defects. (B) Schematic of a mouse hindlimb showing the pathway that promotes limb bud outgrowth. Pitx2, which is expressed specifically in the left LPM, is an L-R influencer that can disrupt limb symmetry in the absence of Pitx1, which thereby acts as a wedge to buffer against underlying Pitx2 asymmetry.