Abstract

The zebrafish is a powerful model system for investigating embryonic vertebrate hematopoiesis, allowing for the critical in vivo analysis of cell lineage determination. In this study, we identify zebrafish myeloerythroid progenitor cells (MPCs) that are likely to represent the functional equivalent of mammalian common myeloid progenitors. Utilizing transgenic pu.1-GFP fish, real-time MPC differentiation was correlated with dynamic changes in cell motility, morphology, and gene expression. Unlike mammalian hematopoiesis, embryonic zebrafish myelopoiesis and erythropoiesis occur in anatomically separate locations. Gene knockdown experiments and transplantation assays demonstrated the reciprocal negative regulation of pu.1 and gata1 and their non-cell-autonomous regulation that determines myeloid versus erythroid MPC fate in the distinct blood-forming regions. Furthermore, forced expression of pu.1 in the bloodless mutant cloche resulted in myelopoietic rescue, providing intriguing evidence that this gene can function in the absence of some stem cell genes, such as scl, in governing myelopoiesis.