Fig. 1. (A) Details of the Hoxb4 locus are shown along with an indication of its position within the Hoxb cluster. The first transcription start site (P1) (Gutman et al., 1994) is indicated with an arrow. Black and white boxes represent coding and untranslated sequences, respectively. The hatched region within exon 2 indicates the position of the homeobox. The positions and specificities of known regulatory regions (A, B, C) are indicated above the locus (Whiting et al., 1991). The ambiguous function of region B is indicated by a question mark. B, BglII; Hb, hindbrain; H; HindIII; N, NcoI; P, PstI; r, rhombomere; S, SalI; SC, spinal cord; so, somite. (B) Constructs used in this study. Fragments of the Hoxb4 locus are represented as in A. hsp and pA indicate the hsp68 promoter and SV40 polyadenylation signal, respectively. Exp denotes the total number of transgenic F₀ embryos and lines showing a consistent pattern of X-gal staining for each construct. Asterisk indicates that analysis of construct CHZ has been reported previously (Gilthorpe et al., 2002) and the data are given here for comparison.