Erythroid development is influenced by cytokines: erythropoietin (Epo) and stem cell factor (SCF), which works synergistically. Epo is the major regulator of erythropoiesis, which is produced by kidneys with an inverse relation to oxygen availability. The Epo gene expression is controlled by HIF-1alpha. After binding the Epo-receptor, it activates the JAK2-STAT5 pathway, PI3K-AKT pathway and so on. Finally, these signals enhance erythropoiesis. All hematopoietic cells are derived from the hematopoietic stem cells (HSCs). HSCs are localizing in a two different bone-marrow microenvironment: the osteoblastic niche and the vascular niche. The erythroid progenitors are induced from HSCs mainly by the membrane bound SCF derived from the bone-marrow stromal cells and then entrapped in the extracellular matrix.