Fig. 4. Transgenic analysis identifies a 560 bp Pax3-responsive region within the Msx2 promoter. (A) Schematic maps of Msx2-lacZ transgene constructs. 
1 and 2 contain a lacZ gene inserted in the first exon. 3 and 4 comprise the indicated promoter fragments fused to an hsp68 minimal promoter and lacZ reporter. (B-N) Effect of the Splotch mutation on transgene expression in E9-9.5 embryos. (B,C,L) Dorsal views of whole-mount preparations. Brackets indicate the approximate location of the cardiac neural crest. Note increased staining in the postotic hindbrain of 1Msx2-lacZ, 2Msx2-lacZ and 4Msx2-lacZ transgenes in Pax3Sp/Sp embryos. The embryos in L are at a slightly earlier stage than those in B,C, which accounts for the lower overall level of staining in the hindbrain and neural tube. Embryos in B and L were sectioned in the transverse plane. Shown below the whole mounts are sections (D,E,M,N) at the levels indicated by arrows to the right of whole mounts. ß-gal expression is imaged in dark field. Pink indicates a low to moderate signal, blue a more intense signal. Note the expansion of ß-gal expression into the dorsal (arrowhead) and lateral (arrow) regions of the neural tube of Splotch mutant embryos, mirroring the change in endogenous Msx2 expression (Fig. 3). (F,G) Longitudinal sections through the hindbrains of E9.5 1Msx2-lacZ embryos. (H-K) Higher magnification views of the boxed regions in F,G. Note increased staining in both preotic crest and cardiac crest in Splotch embryos compared with wild type. cc, cardiac crest; n, neural fold; o, otic vesicle; pc, preotic crest; r5, rhombomere 5. Scale bars: 100 µm.
