09-P049 DeadEasy: Automatic cell counting in vivo in Drosophila

myeloid cell development in Xenopus. We show that cebpa is one of the first known hematopoietic genes expressed in the embryo. Lossand gain-of-function studies show that it is both necessary and sufficient for the development of functional myeloid cells. In addition, we show that cebpa misexpression leads to the precocious induction of myeloid cell markers in pluripotent prospective ectodermal cells, without the cells transitioning through a general mesodermal state. Finally we use live imaging to show that cebpa expressing cells exhibit many attributes of terminally differentiated myeloid cells, such as highly active migratory behavior, the ability to quickly and efficiently migrate toward wounds and phagocytose bacteria, and the ability to enter the circulation. Thus C/EPB alpha is the first known single factor capable of initiating an entire myelopoeisis pathway in pluripotent cells in the embryo.