Fig. 8. Deletion of the -63 kb to -48 kb region reveals an additional element(s) directing a second phase of limb expression. Transgenic embryos at E13.5 where nlacZ expression is directed by BAC195APZ (A) or by BAC195APZ63-48 (B). In C, an embryo with the -58/-48 Myf5-nlacZ transgene is shown. Comparison of the expression patterns of the limbs between embryos of BAC195APZ (D,F,H,J) and BAC195APZ63-48 (E,G,I,K) transgenic lines. (E) At E12.5, all pre-muscle masses show weak X-gal staining, not seen in the hindlimb at this stage (not shown). (F,G) By E13.5, the forelimb expression pattern driven by the two constructs is similar. (I) Very weak expression is detected in hindlimb pre-muscle masses. (J,K) By E14.5, the hindlimb expression pattern driven by the two BAC constructs is indistinguishable.