a–c, Expression of Hoxa10 (a), Hoxa11 (b) and Hoxa13 (c) in wild-type limb bud from embryonic day (E) 11.5 mouse. d, Replacement of the Hoxa11 gene with the PGK-neomycin cassette (Hoxa11Neo; scheme to the left), results in neomycin expression both in the proximal and distal domains. e, f, Expression of all antisense transcripts (e) and antisense transcripts overlapping with Hoxa11 exon 1 (f) in E11.5 wild-type limb. Schemes of the antisense transcripts and the probes used (blue boxes) are on the left. Note that the antisense transcripts overlapping with Hoxa11 exon 1 (Hoxa11as-b) are distally restricted (f), reminiscent of Hoxa13 expression (c) and mutually exclusive with the Hoxa11 pattern (b). g, Deletion of the antisense transcript start sites in Hoxa11 exon 1, via replacement of most of exon 1 with the eGFP coding sequence (Hoxa11eGFP; scheme to the left) and expression of gfp under the control of the Hoxa11 promoter (right). Original magnification, ×31.5 (for all images).