Fig. 3. ß-galactosidase staining of mouse embryos harboring the Mef2c-lacZ transgene. F₀ embryos harboring construct 1, containing the region from -6.6 kb to +77 bp (see Fig. 2), were stained for lacZ expression. A neural crest enhancer (NCE) was also included in this construct as a positive control for lacZ activity. (A) An E9.5 transgenic embryo shows lacZ expression in rostral somites and weaker activity in more caudal somites. (B) Dorsal view of an E10.5 embryo shows expression in rostral and caudal somites. (C) Transverse section of an E10.5 embryo at the level of thoracic somites demonstrates lacZ staining in the myotome. (D) Dorsal view of an E11.5 embryo shows staining in somites and ventral myoblasts (vm). (E) At E14.5, transgene expression is evident throughout much of the embryonic musculature. Also evident is pharyngeal arch expression driven by the NCE (A,D), which is indicated by arrowheads. Arrows, somites; d, deltoid; ld, latissimus dorsi; m, myotome; t, trapezius; vm, ventral myoblasts.