In a paper published online in advance in Science this week, an international team led by investigators at King's College London shows that, in developing mice, the transcription factor Myb is required for the development of hematopoietic stem cells as well as for all CD11b^high monocytes and macrophages, though it is "dispensable for yolk sac macrophages and for the development of YS [yolk sac]-derived F4/80bright macrophages in several tissues." Overall, the authors sa