A fork in the road.

In this issue of Blood, Xavier-Ferrucio et al provide new insights into the mechanisms responsible for the well-documented finding of thrombocytosis in patients with iron deficiency anemia. By using mouse and human models, they document that a low iron content in the bone marrow environment affects the megakaryocyte-erythroid progenitors (MEPs). This occurs because of induced alteration in their metabolism, attenuation of ERK signaling, slowing of cell proliferation, and biasing of the MEPs toward megakaryocyte commitment, which ultimately results in thrombocytosis and anemia.