Fig. 4.

Reduced dose of Msx2 rescues ectopic osteogenesis and Bmp signaling in the supraorbital ridge of Foxc1 mutant embryos. (A-F) ALP expression in the supraorbital ridge in E12.5 wild-type, Foxc1, Msx2 and compound mutant embryos. There is near-normal expression of ALP in the Foxc1^ch/+; Msx2^+/– compound heterozygous mutant (E) versus the Foxc1 heterozygous mutant (B). Also note the partial rescue in the Foxc1^ch/ch; Msx2^+/– mutant (F) compared with the Foxc1 homozygous mutant (C). (G) Numbers of embryos harvested for this experiment. ^*N/A, not applicable. (H) We measured the level of ALP expression in the supraorbital ridge by counting the purple pixels in two areas: p (primordium) and e (ectopic). (I) The influence of Msx2 dose on ALP expression in Foxc1 mutants was statistically significant in area e (^*P<0.05, ^**P<0.005). (J-M) Bmp signaling activity in E13 embryos was detected by P-Smad1/5/8 immunohistochemistry. P-Smad1/5/8 expansion is partially rescued: compare the area spanned by the white arrow from p to e in K with the corresponding area in M. (N) Significant reduction of P-Smad1/5/8 signal in area e in Foxc1^ch/+; Msx2^+/– mutant embryo in comparison with Foxc1^ch/+ mutant (^*P<5.00×10^–6). Significance was assessed by Student’s t-test. Error bars indicate s.d.