c-Myb is essential for early T cell development

The c-Myb transcription factor is important for fetal hematopoiesis and has been proposed to mediate later stages of lymphocyte development. Using hom ozygous null c-Myb/Rag1 chimeric mice, we have determined that c-Myb plays an important role in the differentiation of macrophages and lymphocytes fro m precursor stem cells. We also determine that deletion of c-Myb leads to a complete block in early T cell development just before the oligopotent thy mocyte matures into the definitive T cell precursor. These data indicate th at c-Myb plays an important role at multiple stages of hematopoiesis and is required at an early stage of T cell development.