Fig. 3. An E-box 3' of the Mbh1 gene was required for lacZ expression in the spinal cord. (A) Structure of the transgenes, and the number of transgenic and ß-gal⁺ embryos recorded. The 3' fragments were reversed in Tg7, Tg10 and Tg13. Restriction enzyme sites used for cloning are indicated: Ba, BamHI; Kp, KpnI; Na, NarI, Ps, PstI; Sm, SmaI; Xb, XbaI. ^aThe three embryos expressed lacZ in the midbrain, floor plate or whole body. ^blacZ was expressed in the branchial arch or midbrain. ^cThe three embryos expressed lacZ in the telencephalon, limb or skin. Expression levels of lacZ in these ectopic sites (^a-c) were low. ^dSeven embryos also expressed lacZ in the midbrain and somite. (B-D) Dorsal views of representative ß-gal⁺ embryos harboring Tg8 (B), Tg14 (C) and Tg18 (D). An arrow and an arrowhead indicate the ß-gal⁺ midbrain and somite, respectively. Scale bars: in B, 1 mm for B,C; in D, 1 mm. (E) Nucleotide sequence comparison of the 123-base sequence among the three species. Residues identical in the three species are boxed.