Fig. 6. Absence of Six1 does not lead to an increase in apoptosis in Six1-expressing cells. TUNEL assays at the forelimb bud level of E11 Six1^–/– and Six1^+/– embryos (A,B,D,E). Six1-expressing cells are detected by an antibody against ß-galactosidase (B,C,E,F). (A-C) Apoptosis in Six1^–/– embryos (A) is not increased in the dorsal and ventral aspects of the limb bud where Six1-positive migrating myogenic cells are detected (C), as revealed by double staining (B). (D-F) In Six1^+/– embryos, similarly no massive apoptosis is detected in ventral and dorsal regions of the limbs (D) where Six1-positive cells accumulate (F), as revealed by double staining (E).