Phenotypic complementation establishes requirements for specific POU domain and generic transactivation function of...

Transcription factors of the POU family govern cell fate through combinatorial interactions with coactivators and corepressors. The POU factor Oct-3/4 can define differentiation, dedifferentation, or self-renewal of pluripotent embryonic stem (ES) cells in a sensitive, dose-dependent manner (H. Niwa, J.-I. Miyazali, and A. G. Smith, Nat. Genet. 24:372-376, 2000). Here we have developed a complementation assay based on the ability of Oct-3/4 transgenes to rescue self-renewal in conditionally null ES cells and used this to define which domains of Oct-3/4 are required to sustain the undifferentiated stem cell phenotype. Surprisingly, we found that molecules lacking either the N-terminal or C-terminal transactivation domain, though not both, can effectively replace full-length Oct-3/4. Furthermore, a fusion of the heterologous transactivation domain of Oct-2 to the Oct-3/4 POU domain can also sustain self-renewal. Thus, the unique function of Oct-3/4 in ES cell propagation resides in combination of the specific POU domain with a generic proline-rich transactivation domain. Interestingly, however, Oct-3/4 target gene expression elicited by the N- and C-terminal transactivation domains is not identical, indicating that at least one class of genes activated by Oct-3/4 is not required for ES cell propagation.