Erythropoietin hormone which stimulates RBC formation is produced by:

Erythropoietin (Epo) is a glycoprotein that promotes the proliferation and differentiation of erythrocyte precursors. The juxtaglomerular kidney cells that make EPO are specialized and are sensitive to low oxygen levels in the blood coming into the kidney. After being released into the bloodstream it binds with receptors in the bone marrow, where it stimulates the production of red blood cells (erythrocytes). Medically, EPO is used to treat certain forms of anaemia.