Schematic representation of Se function during stress erythropoiesis. Mouse stress erythroid progenitors (SEP) migrate from the bone marrow to the spleen, where Se acts to increase SEP numbers and differentiation to erythroid precursors. Optimal precursor maturation relies on the formation of functional EBIs. Se promotes the differentiation of island macrophages by upregulating Spic expression in monocytes. Professional illustration by Patrick Lane, ScEYEnce Studios.