Fig. 4. Expression patterns of Msx2 and Bmp4 in Msx1 mutant digits. (A,B) Msx2 whole-mount in situ hybridization of stage 11 wild-type (A) and Msx1 mutant (B) digits that were processed and imaged in parallel, showing an upregulation of Msx2 expression in the Msx1 mutant. (C) Frontal section of an Msx1 mutant digit showing the expansion of the Msx2 expression domain (compare with Fig. 1I). (D,E) Bmp4 whole-mount in situ hybridization of stage 11 wild-type (D) and Msx1 mutant (E) digits that were processed and imaged in parallel. Bmp4 expression is downregulated in the Msx1 mutant digit. (F) Frontal section of an Msx1 mutant digit showing compression of the Bmp4 expression domain to the apical mesenchyme (compare with Fig. 1J).