Figure 1

Moa forelimb structure and forelimb initiation gene network. A. The moa wing skeleture consists of a small finger-sized bone that represents the fusion of remnants of the coracoid and scapula to form the scapulocoracoid (right). A fully developed wing skeleton (light grey) is shown superimposed onto a moa sillouette for comparison. The scapulocoracoid is circled and shown in black. B. The central gene network essential for forelimb initiation. A Hox expression code initiates the expression of retinaldehyde dehydrogenase 2 (r2) and tbx5 (t5) in the lateral plate mesoderm (LPM) [41]. Tbx5, in combination with YAP and TAZ (Y, T; [50]), interacts with Sall4 (s4) [42] to activate fgf10 (f10) and subsequently fgf8 (f8) in the limb apical ectodermal ridge (AER). An additional activator of forelimb initiation Wnt2b (W2b) possibly acts upstream of, or in conjunction with tbx5 through the transcription activators LEF/TCF and beta-catenin (ltβ) [3, 51].