Fig. 7. Transgenic assay indicates HOX/PBC sites are necessary for enhancer activity in the hindbrain. (A,F) Dorsal (A) and lateral (F) views of reporter expression in 10.0 dpc embryos directed by a fragment that spans the conserved block from the mouse Hoxa3 locus in which the KrA site has been mutated (construct 7, Fig. 4). The activity of this fragment is dependent upon the late control elements. (B,C,G,H) When the HOX/PBC-A (B,G) or the HOX/PBC-B (C,H) sites are mutated (constructs 8 and 9, respectively), expression in r5/r6 is reduced. (D,I) Reporter staining is completely abolished when both HOX/PBC sites (construct 10) are mutated. (E,J) Mutations in the Prep/Meis motif (construct 11) have no effect on reporter activity. All embryos are at 10.0 dpc. The respective constructs and mutated sites are noted at the bottom.