MYB is an Essential Regulator of Primitive Human Hematopoiesis in Pluripotent Stem Cell Differentiation Cultures

MYB is a key regulator of definitive hematopoiesis that plays a critical role in the maintenance and multilineage differentiation of hematopoietic stem cells (HSCs). In vertebrate developmental models, MYB is thought to be dispensable for primitive hematopoiesis. To explore the role of MYB in human hematopoietic development, we have subjected human pluripotent stem cells (hPSCs) to mono- and bi-allelic gene targeting followed by hematopoietic differentiation in defined culture conditions. Here we show that MYB plays a central role in the development of human primitive blood cells. MYB expression was hematopoietic-specific and its induction coincided with emergence of the earliest primitive blood cells. Bi-allelic inactivation of MYB most severely affected the primitive erythroid progenitors of greater proliferative capacity and multilineage hematopoietic progenitors. The initial phase of the hematopoietic differentiation was not affected by the bi-allelic gene deficiency, but maturation of the primitive myeloid cells was found to be MYB-depended. Rescuing MYB expression in MYB-null cells shows that the gene is required for both development and proliferation of primitive clonogenic progenitors. In addition, our findings suggest that human primitive hematopoiesis emerge in several developmental cohorts.