Fig. 4. The 52 bp element responds to BMP signaling in a subset of sites relative to the parental 560 bp fragment. Expression and BMP-responsiveness of the 52bpMsx2-hsplacZ transgene were assessed in a developmental series of embryos and tissues from E8.5 to E13.5. A total of five transgenic lines were compared, with closely similar results (Table 1). (A-D) Overnight lacZ stains of embryo whole mounts. (E,F) Midsagittal sections of whole mounts stained for lacZ. The embryo in E was embedded in plastic and photographed in dark field, showing lacZ activity in pink. Note expression in the allantois (A,B), pharyngeal arches (A-C,E,F) and cardiac outflow tract (A-F). Expression in the pharyngeal region was restricted to tissues adjacent to the pharyngeal endoderm and cardiac outflow tract (E,F). At E11.5, expression persisted in the outflow tract, and was evident in the genital region, the anterior limb bud mesenchyme, the otic vesicle and the eye (D). (G-I) High-magnification views of forelimbs of E12.5-E13.5 embryos stained for lacZ (anterior to right). (G) Expression of the parental 560 bp transgene. (H,I) Expression of the 52 bp transgene in the anterior and interdigital limb mesenchyme. (J,K) lacZ expression in bead-implanted limbs. a, allantois; pam, pharyngeal arch mesenchyme; ot, outflow tract; al, anterior limb; gr, genital region; ov, otic vesicle; e, eye.