Fig. 2. Identification and activity of a chick Hoxa3 r5/r6 enhancer in mouse and chick embryos. (A) Diagram of the upstream region of the chick Hoxa3 locus and fragments used to make constructs for chick and mouse transgenic analysis. On the right is indicated the construct number (#) and also the number (N) of transgenic embryos, all reproducibly expressing the constructs in r5/r6 in the mouse analysis. (B,E) Reporter expression at HH16 in the chick neural tube electroporated on the right side with construct c1. Anterior expression reproducibly (n=12) maps to r4/r5. (C,F) Dorsal (C) and lateral (F) views of transgene expression in 10.0 dpc mouse embryos carrying construct c1. Note that the pattern and anterior boundary is the same as that detected in chick embryos (see B,E). (D,G) Dorsal (D) and lateral (G) views of reporter expression in r5/r6 directed by a region in construct c1 conserved with the mouse Hoxa3 gene (see Fig. 3). nc, neural crest; ov, otic vesicle. The black arrowheads indicate the r4/r5 boundary. All mouse embryos shown are at 10.0 dpc.