Fig. 1. A territory with new characteristics, rx, is formed in the place of presumptive r4 in the Hoxa1-/-/Hoxb1 3'RARE-/-embryos. Wild-type (a,d,g), Hoxa1-/- (b,e,h) and Hoxa1-/-/Hoxb1 3'RARE-/- (c,f,i) embryos were processed for whole-mount in situ hybridisation with kr/Krox20 (a-c), Hoxb2 (d-f) and Hoxa2 (g-i) antisense riboprobes. Double staining with kr/Krox20 shows that the r4 territory of wild-type embryos defined by non-expressing cells (vertical bar in a) was significantly reduced but not eliminated, to similar extents in both Hoxa1-/- and Hoxa1-/-/Hoxb1 3'RARE-/- (vertical bars in b,c, respectively). Hoxb2 expression is continuous throughout the r3-r6 region in both wild-type and Hoxa1-/- embryos (d,e) but not in Hoxa1-/-/Hoxb1 3'RARE-/- embryos (f). There are Hoxb2 non-expressing cells intermingled with r3 cells in both Hoxa1-/-and Hoxa1-/-/Hoxb1 3'RARE-/-embryos (arrowheads in e,f). Expression of Hoxa2 is continuous throughout the r2-r6 region in wild-type (g) as well as Hoxa1-/- (h) and Hoxa1-/-/Hoxb1 3'RARE-/- (i) embryos.
