Impact of the c-Myb^E308G mutation on mouse myelopoiesis and dendritic cell development

Booreana mice carrying the c-Myb^308G point mutation were analyzed to determine changes in early hematopoiesis in the bone marrow and among mature cells in the periphery. This point mutation led to increased numbers of early hematopoietic stem and progenitor cells (HSPCs), with a subsequent reduction in the development of B cells, erythroid cells, and neutrophils, and increased numbers of myeloid cells and granulocytes. Myelopoiesis was further investigated by way of particular subsets affected. A specific question addressed whether booreana mice contained increased numbers of dendritic-like cells (L-DC subset) recently identified in the spleen, since L-DCs arise in vitro by direct differentiation from HSPCs co-cultured over splenic stroma. The non-lethal c-Myb mutation in booreana mice was associated with significantly lower representation of splenic CD8^- conventional dendritic cells (cDCs), inflammatory monocytes, and neutrophils compared to wild-type mice. This result confirmed the bone marrow origin of progenitors for these subsets since c-Myb is essential for their development. Production of L-DCs and resident monocytes was not affected by the c-Myb^E308G mutation. These subsets may derive from different progenitors than those in bone marrow, and are potentially established in the spleen during embryogenesis. An alternative explanation may be needed for why there was no change in CD8⁺ cDCs in booreana spleen since these cells are known to derive from common dendritic progenitors in bone marrow.