Fig. 9. Expression pattern of the transgene Myf5-VIII in somites of mouse embryos. lacZ staining on a whole-mount embryo at E9.5/10 indicates transgene activity in all somites including cervical somites (A). Transgene activity in the more caudal (younger) somites (C,E) is preferentially associated with the posterior half, but this is not the case in older somites (D,F). Serial transverse sections of E9.5/10 embryo show dermomyotomal expression in caudal somites (F) that gradually shifts to the myotome in rostral somites that are more mature (E,D). A sagittal section of the cranial somites confirms the expression in myotomes (C). Transgene activity in somites of E13.5 embryos is downregulated (B). Weak expression is seen in proximal muscles of fore- and hindlimbs at the dorsal side.