Basophilic stippling is indicative of disturbed erythropoiesis. This is termed "extramedullary erythropoiesis". Transferrin plays a key role in areas where erythropoiesis and active cell division occur. Erythropoietin or EPO is a hormone naturally produced by the kidneys that stimulates erythropoiesis. Hence SBDS is critical for normal erythropoiesis . HIF stimulates the release of VEGF-A, among other functions (including modulation of erythropoiesis). One study found the tea may exert an erythropoiesis boosting effect. LMO2 encodes a cysteine-rich, two LIM domain protein that is required for yolk sac erythropoiesis. Other mechanisms may also play a role, such as reduced erythropoiesis. However, KLF2 and EKLF have been found to interact in embryonic erythropoiesis. It stimulates erythropoiesis (production of red blood cells) in the bone marrow. Increased level of physical activity can cause an increase in erythropoiesis. At this time several developing blood cell lines are available, like erythropoiesis and thrombopoiesis. Without it, definitive erythropoiesis does not take place. Since folate deficiency limits cell division, erythropoiesis (production of red blood cells) is hindered.