Fig. 3. Deletion analysis defines a 220 bp minimal Msx2 element and a 52 bp element required for BMP signaling. (A) Deletion series of lacZ constructs bearing fragments of the 560 bp promoter sequence. The BMP responsiveness of each transgene was assessed by bead implantation; positive response (+), negative response (–). (B,C,E,F,H) lacZ stains of 560 and 220 bp transgenic embryos at E11.5. Expression patterns (B,C) and BMP responsiveness (E,F) are similar. BMP-responsive constructs shared a 52 bp region (A, ^*), deletion of which in the context of the 560 bp transgene resulted in reduced expression (D), and loss of BMP responsiveness in embryos (G) and in 10T1/2 cells (I). Because of diminished transgene activity, the embryo in D was stained overnight (compare with H), while embryos in B and C were stained for 1 (B) and 2 (C) hours.