Fig. 6. Msx2 and Twist cooperatively control the patterning of the frontal bone. (A-F) Skulls of mice with the indicated genotypes were taken at postnatal day 4. Mineralized bone was stained with Alizarin Red S. (G) Measurements of the areas of frontal foramina obtained from several individuals of each genotype. Note that the defect (arrows, B-F) is more severe in Msx2-Twist double heterozygotes than in either individual heterozygote, indicating a cooperative interaction between Msx2 and Twist in the control of frontal bone development. cs, coronal suture; fb, frontal bone; fs, frontal suture; ls, lambdoid suture; pb, parietal bone; pf, parietal foramen; ss, sagittal suture. Scale bar: 2 mm.