XLPOU 1 and XLPOU 2, two novel POU domain genes expressed in the dorsoanterior region of Xenopus embryos.

POU domain genes have been shown to be important in tissue-specific gene regulation during development. We have cloned cDNA's encoding two unique Xenopus laevis POU-domain proteins, XLPOU 1 and XLPOU 2. Sequencing revealed that the POU domain of both of these genes have greater than 90% homology with that of the POU III class of proteins. XLPOU 1 gene expression begins at the neural plate stage, while XLPOU 2 gene expression is first detected at the neurula stage; both XLPOU 1 and XLPOU 2 transcripts continue to be expressed throughout development. In adults, XLPOU 1 expression is restricted to the skin and brain, while XLPOU 2 is observed in the kidney and brain. In dissected embryos, both XLPOU 1 and XLPOU 2 are expressed in the dorsoanterior portion of an early tailbud embryo. Consistent with this localization, uv treatment, a condition that "posteriorizes" embryos, greatly reduces the expression of XLPOU 1 and XLPOU 2. Whole-mount in situ hybridization demonstrates that at the neural fold stage, XLPOU 1 transcripts appear to be localized primarily in the anterior neural plate. In sections of embryos, in situ hybridization shows that XLPOU 1 transcripts are localized mostly in the anterior region of the nerve cord of neurula stage embryos. In tailbud stage embryos, the XLPOU 1 transcripts are found predominantly in the eye and brain, with weak expression along the length of the nerve cord. We believe that XLPOU 1 and XLPOU 2, because of their localized and early expression in embryos, may play an important role in the specification of neuronal phenotypes.