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The caudal-related (Cdx) homeodomain transcription factors have a conserved role in the development of posterior structures in both vertebrates and invertebrates. A particularly interesting finding is that Cdx proteins have an important function in the regulation of expression from a subset of Hox genes. In this study, we report the cloning of cDNAs from the Cdx genes of the amphibian Xenopus tropicalis. Xenopus tropicalis is a diploid species, related to the commonly used laboratory animal Xenopus laevis, and has attracted attention recently as a potential genetic model for animal development. The Xenopus tropicalis cDNAs, Xtcad1, Xtcad2, and Xtcad3, show between 88 and 94% sequence identity with their Xenopus laevis orthologues. This finding corresponds to between 90 and 95% identity at the level of derived amino acid sequence. We also present a detailed description of Xtcad1, Xtcad2, and Xtcad3 expression during normal development. In common with the Cdx genes of other vertebrates, the Xenopus tropicalis Cdx genes show overlapping and dynamic patterns of expression in posterior regions of the embryo through the early stages of development.
Figure 3. The expression of Xtcad1 during normal development. Whole-mount in situ hybridizations showing the expression of Xtcad1 at various stages. A: Vegetal view of late blastula stage 9 embryo. B: Dorsal side view of early gastrula stage 10+ embryo. The animal hemisphere is to the top, the dorsal lip is visible as a pigmented line. C: Ventral side view of stage 10+ embryo. D: Vegetal view of gastrula stage 10.5 embryo; dorsal is to the top. E: Vegetal view of gastrula stage 12 embryo; dorsal is to the top. F: Dorsal view of late gastrula/early neurula stage 13 embryo; anterior is to the left. G: Dorsal view of late neurula stage 20 embryo. H: Parasagittal open face view of a stage 20 embryo bisected along the anteroposterior axis; anterior is to the left, dorsal is to the top. I: Lateral view of the posterior region from a stage 30 embryo. J: Lateral view of the tail forming region of a stage 33 embryo. K: Lateral view of a dissected gut from a stage 40 embryo; anterior is to the left. L: Lateral view of dissected gut from stage 42 embryo. bp, position of blastopore; cnh, chordoneural hinge; end, endoderm; mes, mesoderm; nec, neuroenteric canal; nt, neural tube; ntc, notochord; pw, posterior wall of neuroenteric canal; st, stomach
Figure 4. The expression of Xtcad2 during normal development. A-L: Whole-mount in situ hybridizations showing the expression of Xtcad2 at various stages. Stages and orientation are per Figure 3, except D, which is a vegetal view of a stage 11 embryo.
Figure 5. The expression of Xtcad3 during normal development. A-L: Whole-mount in situ hybridizations showing the expression of Xtcad3 at various stages. Stages and orientation are per Figure 3.