Fig. 1. B4B2A5m construct and expression in E9.5 embryos. (A) Schematic of the B4B2A5m construct. HD, homeodomain; SVpA, SV40 polyadenylation signal; CR5, CR6, CR7 and CR8 are the primers used in PCR and RT-PCR assays (for details see Materials and Methods section). (B,C) Hoxa5m transgene expression in E9.5 embryos, visualized by in toto hybridization. (B) Two sibling embryos: one heterozygous transgenic (left) and one control (right). Hoxa5 transgene is observed in r3 and r5, and in the somites. (C) Flat mount of the rhombencephalon of a B4B2A5m mouse, illustrating Hoxa5m transgene expression in r3 and r5 (A, anterior; P, posterior).