Fig. 2.

Expression of mouse HoxA and Tetraodon HoxAa genes in either wild type or tni HoxAa mice. In situ hybridization was performed on E11.5 wild type and transgenic embryos (genotypes are indicated on the right hand side). Wild type embryos were analyzed with mouse specific probes to visualize the expression of the endogenous Hoxa genes and with Tetraodon specific probes to exclude potential cross reactivity with the endogenous mouse genes. Tni HoxAa transgenic embryos were processed for Tetraodon specific probes. Probe names are indicated above as well as whether the probe used was for a wild type or transgenic specimen (indicated on the left hand side). The expression pattern of the Tetraodon probes in the transgenic context shows the expected collinear pattern with Hoxa9a being expressed most anteriorly (although not as far as the endogenous mouse Hoxa9) and Hoxa13a restricted to the posterior most tail. There is however marginal differentiation, if any, between the anterior expression limits of Hoxa10a and Hoxa11a. A clear difference is observed in expression between mouse Hoxa11, which has an anterior expression limit close to the posterior limit of the hind limb buds, and the Tetraodon Hoxa11a, that has a limit around three to four somites more anterior, coinciding with the anterior limit of the hind limb buds (the anterior level of axial expression in both wild type and tni HoxAa panels is indicated with a dotted line). This particular area where the difference is observed is the part of the body where sacral transformations are scored (Fig. 1). The lower row shows that there is no cross reactivity in the in situ hybridization between the Tetraodon probes and the endogenous mouse genes.