Fig. 2.

Shox2 and Tbx4 expression during murine limb development. A: Whole mount in situ hybridization on mouse embryos of different developmental stages (limbs or limb developing regions are indicated by arrows). Shox2 expression starts at E9.5 in the forelimb buds (a), is expressed throughout fore- and hindlimb buds at E10.5 (b), and from E11.5–E13.5 restricted to the proximal part of the limbs (c–e). Tbx4 hindlimb expression starts at E9.5 in the lateral plate mesoderm (f), continues throughout E10.5–E12.5 (g–i), and restricts distally at E13.5 (j). In the forelimbs, distinct Tbx4 staining is visible at E10.5-E12.5 (g–i). In addition, a diffuse Tbx4 expression can be seen at E11.5 (h, arrowhead), which again restricts distally from E12.5 onward (i, j, arrowheads). B: In situ hybridization on 12 µm adjacent limb sections of different developmental stages. Dorsal sections of the forelimb (a–i) and medial sections of the hindlimbs (a′-i′) are presented. The Tbx4 expression domain of the forelimb and the corresponding Shox2 expression are indicated at E10.5 (a, b), E11.5 (d, e), and E12.5 (g, h) by arrowheads. Sox9 and Col2a1 were used as markers for condensing mesenchyme, and cartilaginous skeletal elements, respectively. Hindlimb expression of Shox2 (g′) and Tbx4 (h′) surrounding the cartilaginous elements at E12.5 are indicated by arrows.