Tbx5 is expressed in the forelimb(field) and at early stages at a much weaker level also in the rostral flank (Rallis et al., 2003; Gibson-Brown et al., 1998).
Unexpectedly we detect homogenous Tbx5 expression throughout the entire antero-posterior extent of the pre-cloacal somatopleure (Figs. 7B, E and S8), without any indication of restriction to a putative forelimb region.
Thus, despite collinear Hox expression in the lateral plate mesoderm, no forelimb buds are induced in the snake and the forelimb gene Tbx5 shows deregionalized expression that seems independent from the Hox expression pattern (schematically depicted in Fig. 7F).