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Fig. 1. The initial Hox expression is localised in the non-organiser mesoderm. Whole mount in situ hybridisation of Hox genes and mesodermal marker genes. (A–D) Vegetal view (organiser is up) of midgastrula stage embryos stained for Hoxd-1 (A), which shows colocalisation with the mesodermal marker Xbra (B) with the exception
of a gap in the organiser region [indicated by chordin (chd) expression (C)]. The expression domain of the secreted antiorganiser signal BMP-4 (i.e. the region of highest levels of secreted protein) is localised in similar embryonic regions (D). (E– J) Dissections were made across the initial Hox expression domain close to the organiser (O) (as indicated in the schematic drawings). In each case, one-half of an embryo shows the early expression of either Hoxd-1 at stage 10.5 (E), Hoxc-6 at stage 11.5 (G) or Hoxa-7 at stage 12.5 (I), whilst the corresponding second half is stained for the mesodermal marker Xbra (F, H, J). The early expression of the different Hox genes is located within the Xbra domain. The arrowheads point to corresponding positions in the two half embryos. |
