NPM1 mutant in zebrafish model. In zebrafish, where mutant NPM1 was expressed ubiquitously, not only did it cause expansion of primitive myeloid cells but it also resulted in increased numbers of both definitive erythromyeloid progenitors (gata1⁺/lmo2^bright) and hematopoietic stem cells (c-myb⁺/cd41⁺) in the ventral wall of the aorta.