activin

noun

ac·​ti·​vin ˈak-ti-ˌvin, ak-ˈti-vən 

: a glycoprotein hormone produced especially in the pituitary gland and gonads that stimulates the secretion of follicle-stimulating hormone, induces the formation of mesoderm during embryological development, and modulates the proliferation and differentiation of red-blood-cell precursors during hematopoiesis compare inhibin