Figure 2: Schematic representation of known and proposed p63 pathways relevant for limb development and the onset of ectrodactyly. P-cadherin is a known disease gene only in human, while Dlx5;Dlx6 are known disease genes only in mice. Dactylin has been proposed as the disease gene for SHFM-III but no evidence for this is currently available. The most likely disease gene is FGF8 (see text), regulated by both p63 and Dlx proteins by cis- and trans-acting binding elements. The expression of FGF8 and the stratification/maintenance/function of the AER are mutually essential (indicated by a double arrow). Disease genes are framed in boxes (solid for known or highly probable disease genes, dashed for putative ones); regulations are indicated with lines or arrows (solid for known or highly probable regulations, dashed for putative ones).