Fig. 5. Hox-like Cdx expression in embryos at gastrulation and early somite stages (A-C). Expression of the three Cdx genes in the primitive streak (ps) resembling that of 3' Hox genes (see Fig. 2). Cdx2 and Cdx4 are also expressed at the base of the allantois (all), and Cdx2 is expressed in the chorionic ectoderm (ch). Cdx2 is expressed earlier in the trophectoderm, where it is required for implantation (Chawengsaksophak et al., 1997; Strumpf et al., 2005). (D-F) The three Cdx genes are expressed strongly in posterior embryonic tissues (all three germ layers) at somite stages (anterior is towards the left). (D) The expression of Cdx1 extends to more anterior positions than that of Cdx2 (E) and Cdx4 (F). At later stages, Cdx genes are expressed in gene-specific patterns in the gut endoderm (not shown) (see Beck et al., 2000). Scale bars: 100 µm. ps, primitive streak.