Characterization of the Xenopus Hox 2.4 gene and identification of control elements in its intron.

We report on the Xenopus homolog of the Hox 2.4 gene. This gene occupies the next to 5'-most position in the Xenopus Hox2 complex. Hox 2.4 RNA is first detected at the early neurula stage, reaching a peak at the early tailbud stage, and is localized in the middle and posterior portions of the embryos. Antibodies raised against a fusion protein show expression of Hox 2.4 protein in Xenopus embryos in a band located in the mid spinal cord. Thus, the protein is expressed in a narrower domain than that of Hox 2.4 mRNA. The Xenopus Hox 2.4 antibody cross-reacts readily with mouse embryonic tissue, where the protein is detected in migrating neural crest cells, the dorsal portion of the spinal cord, somites, lateral plate mesoderm, and in the forelimb bud. The Xenopus Hox 2.4 intron shares considerable sequence identity with the intron in the mouse homolog. A reporter gene containing an element from this intron which can bind homeodomain proteins is activated following microinjection into Xenopus embryos. The short distance between the end of the Hox 2.4 cDNA and the start site of the neighboring gene in the complex raises the possibility that this transcriptional element might be shared by two Hox genes.