Abstract
A critical aspect of mammalian development involves the actions of dedicated repressors/corepressors to prevent unregulated gene activation programs that would initiate specific cell determination events. While the role of NCoR/SMRT corepressors in nuclear receptor actions is well documented, we here report that a previously unrecognized functional interaction between SMRT and a forkhead protein, FOXP1, is required for cardiac growth and regulation of macrophage differentiation. Our studies demonstrate that SMRT and FOXP1 define a functional biological unit required to orchestrate specific programs critical for mammalian organogenesis, linking developmental roles of FOX to a specific corepressor.