Fig. 8. Analysis of regulatory interactions between Msx2 and Twist in the developing frontal bone. In situ hybridization was used to assess Msx2 expression in Twist^+/– mutant embryos and Twist expression in Msx2^–/– embryos. (A-F) Msx2 probe hybridized with wild-type and Twist mutant heads. (G-L) Twist probe hybridized with wild-type and Msx2 mutant heads. (A-D,G-J) Embryo wholemounts at E10.5 and E11.5 hybridized with digoxigenin-labeled probes. Arrowheads point to the site of the frontal bone primordium. (E,F,K,L) In situ hybridization of radiolabeled (³³P) probes with tissue sections through frontal bone rudiments at E12.5. Note apparent lack of change in Msx2 expression in Twist mutant, and Twist expression in Msx2 mutant at E10.5, E11.5 and E12.5. ch, cerebral hemisphere; e, eye; fn, frontonasal process. Scale bars: 200 µm.