Expression of the Xhox3 Homeobox Protein in Xenopus Embryos: Blocking Its Early Function Suggests the Requirement of Xhox3 for Normal Posterior Development: (axial pattern/central nervous system/embryonic mesoderm/homeobox gene/Xenopus laevis).

Antibodies directed against the product of the Xenopus homeobox gene Xhox3 were raised and used to localize the expression of Xhox3 in the embryo at different stages of development. These studies suggest that endogenous Xhox3 protein is distributed in a graded fashion in the nuclei of mesodermal cells along the anterior-posterior (A-P) and dorso-ventral (D-V) axes in the postgastrula embryo with low levels in anterior and ventral regions and higher levels in posterior and dorsal regions. Xhox3 protein is also detected at different times in the midbrain, spinal cord and hindbrain. In the hindbrain, Xhox3 displays different metameric expression patterns in dorsal and ventral regions during early embryogenesis and metamorphosis. We have tested for the early function of Xhox3 by injecting antibodies against the Xhox3 protein into the cytoplasm of developing embryos. A significant number of embryos injected with Xhox3 antibodies show posterior (trunk and tail) deficiencies. This posterior deficient phenotype constitutes the opposite of the anterior (head) deficient phenotype obtained after overexpresson of Xhox3 reported previously. These results suggest that expression of Xhox3 in the posterior mesoderm is necessary for posterior development and that the graded distribution of Xhox3 in the embryonic mesoderm is required for the development of normal embryonic axial pattern.