Fig. 3. Early effects of Tbx3 misexpression at the forelimb level. In all panels, injected side is rightwards and control side is leftwards. Rostral is towards the top. (A) Levels of Tbx3 transcripts are unaffected at stage 13. (B) By stage 16, Tbx3 transcripts are detected throughout the limb field on the injected side. (C,D) There is no alteration in the rostral border (red arrowheads) of Hoxb8 (C) or Hoxb9 (D) following misexpression of Tbx3. (E) Wnt2b is expressed normally in the early forelimb-forming territory. The limb-forming region extends between somites 15 and 20 (numbered). (F) Tbx5 expression is expanded rostrally. The extent of rostral expansion is indicated with a broken yellow line. Red arrowheads indicate equivalent rostrocaudal levels. (G) Rostral expansion of Hoxc5 expression (indicated with a broken yellow line). Red arrowheads show equivalent rostrocaudal levels. (H). DiI labelling of the prospective limb-forming region and adjacent somites (for axial reference). In the uninjected limb, cells that normally contribute to the posterior limb stay in register with somites at the same axial level (left, arrowhead). On the injected side (right), cells at the same level instead contribute to the inter-limb flank but remain in register with adjacent somites (arrowhead). Somites 17 and 20 are numbered.