Fig. 6. Delineation of the minimal Mef2c skeletal muscle regulatory region. Whole-mount E11.5 embryos expressing constructs 14, 8, 9 and 11 are shown. (A) The nucleotide region from -1058 to +27 (construct 14) was fused directly upstream of the promoterless lacZ cassette and was used to generate F₀ transgenic embryos. At E11.5, ß-gal staining is evident from rostral somites through somites at the level of the hind limb. This expression is weaker and less extensive than that of approximately the same nucleotide region fused to hsp68-lacZ (see Fig. 4C). (B) The nucleotide region from -1058 bp to -507 bp (construct 8) was fused to hsp68-lacZ and used to create F₀ transgenic mice. Small, discrete regions of ß-galactosidase staining are seen in a metameric pattern throughout rostral and caudal somites. (C,D) Transverse sections at the level of forelimb somites of the embryo in B demonstrate that the ß-galactosidase staining marks the extreme dorsomedial aspect of the myotome and ventrolateral myoblasts in the limb. (E) The nucleotide region from -512 bp to +41 bp (construct 9) was fused to hsp68-lacZ and used to create F₀ transgenic mice. Strong lacZ expression is evident throughout the somites and in ventral myoblasts. (F) Transverse section through the somites of an E11.5 embryo expressing construct 9. Expression is evident throughout the myotome. (G) The nucleotide region from -158 bp to +4 bp (construct 11) was fused to hsp68-lacZ and used to create F₀ transgenic mice. Somites and ventral myoblasts show strong lacZ expression. (H) Transverse section through the somites of an E11.5 embryo expressing construct 11. Section shows lacZ expression throughout the myotome. Arrows, somites; m, myotome; arrowheads, dorsomedial myotome; *, limb myoblasts.