In certain aspects, disclosed herein are novel compositions and methods related to either the enhancement or inhibition of erythropoiesis that are useful, for example, in the treatment of anemia or erythrocytosis. For example, disclosed is: - a method of stimulating erythropoiesis in a subject with anemia comprising administering to the subject an agent that binds to MS 1r； - a method of stimulating erythropoiesis in a subject with anemia comprising administering to the subject an agent that binds to IL-17ra； - a method of stimulating erythropoiesis in a subject with anemia comprising administering to the subject an agent that inhibits the binding of WNT5a to RYK. - a method of inhibiting erythropoiesis in a subject with erythrocytosis comprising administering to the subject an agent that binds to MST1r. - a method of inhibiting erythropoiesis in a subject with erythrocytosis comprising administering to the subject an agent that binds to RYK. - a method of inhibiting erythropoiesis in a subject with erythrocytosis comprising administering to the subject an agent that inhibits the binding of IL-17a to IL-17ra.1ts t - methods of determining whether a test agent is an inhibitor of erythropoiesis involving IL.17ra, MST1r or RYK-protein. - a method of expanding or propagating erythroid progenitor cells in vitro comprising culturing the erythroid progenitor cells with an agent that inhibits Ryk or Mst1r to a cell medium comprising the progenitor cells.Dans certains aspects, l'invention concerne de nouvelles compositions et des procédés se rapportant à l'amélioration ou à l'inhibition de l'érythropoïèse qui sont utiles, par exemple, dans le traitement de l'anémie ou de l'érythrocytose.
