Abstract
Tissue-specific nuclear factors can establish gene expression patterns in one cell lineage and suppress that of another. GATA-1 and its cofactor FOG-1 (Zfpm1) regulate erythroid and megakaryocyte development by activating and repressing gene transcription. We previously showed that a conserved motif within the N-terminus of FOG-1 binds the Nucleosome Remodeling and Deacetylase (NuRD) co-repressor complex. Here we report that mice bearing FOG-1 point mutations that disrupt the NuRD interaction display mild anemia with splenomegaly and macrothrombocytopenia, a phenotype reminiscent of that observed in animals bearing germline mutations that disrupt the GATA-1/FOG-1 interaction. Microarray studies revealed relatively few changes in gene expression pattern sin mutant erythroid cells and megakaryocytes. Among the most prominent findings was a marked increase in the levels of Gata2, which is normally silenced in mature erythroid cells. Strikingly, mutant erythroid cells also displayed activation of several genes of the mast cell lineage where FOG-1 is normally extinguished. Furthermore, mutant megakaryocytes misexpressed the same set of mast cell genes, suggesting that NuRD binding by FOG-1 is required to suppress mast cell fate throughout the erythro-megakaryocytic ontogeny. In agreement, prospectively isolated megakaryocytic-erythroid progenitors (MEP) not only exhibited elevated Gata2 and mast cell gene expression, but maintained a multilineage capacity, generating both mast cells and other myeloid lineage cells in culture. Upregulation of mast cell-specific genes is likely the combined consequence of the failure of mutant FOG-1 to function as a repressor and the high levels of GATA-2. Together, these results underscore the importance of the FOG-1-NuRD interaction as an effector of GATA-1 activity. In particular, recruitment of NuRD to GATA-1/FOG-1 regulated genes is required to optimize erythroid and megakaryocytic maturation and restrict a mast cell program in those lineages. More generally, recruitment of NuRD by lineage-specific transcription factors may be a common mechanism to narrow and focus gene expression during tissue maturation.
A hepatic stellate cell gene expression signature associated with outcomes in hepatitis C cirrhosis and hepatocellular carcinoma after curative resection
