Fig. 1. Expression of Hoxb1 and Hoxb9 during mouse embryogenesis. (A-C) Whole-mount in situ hybridisation to detect Hoxb1 (A) or Hoxb9 (B,C) expression in E7.5 embryos. Hoxb1 expression in the primitive streak and adjacent mesoderm (PSM) is seen in a late streak/early bud embryo (A). No Hoxb9 expression is detected in late neural plate stage embryos (B), but is detected in PSM of headfold stage E7.5 embryos (C). (D,E) Whole-mount in situ hybridisation to detect Hoxb1 (D) or Hoxb9 (E) expression in E9.5 embryos. Hoxb1 expression is seen in the tailbud (Tb) and in a segment of the hindbrain (D). A sagittal section of this embryo shows that this latter region is rhombomere 4 (r4) (shown in inset at higher magnification). There is no Hoxb1 expression in the anterior region of the spinal cord (SC). Hoxb9 expression (E) is seen in the SC and Tb, but not in the hindbrain. (F) Immunohistochemistry staining of a near sagittal section from an E7.5 (neural plate stage) embryo, with antibody that recognises Hoxb1, and counterstained with Eosin. Hoxb1 is seen in the PSM. There is no staining in extra-embryonic mesoderm (EEM). (G) DAPI staining of an adjacent E7.5 section that was used for FISH analysis. (H) Immunohistochemistry staining for Hoxb1 on a sagittal section from an E9.5 embryo. The positions of rhombomeres 1 to 4 (r1-4) are indicated. (I) DAPI staining of an adjacent E9.5 section that was used for FISH analysis. Scale bars: 200 µm.