Oncomodulin-1 (OM) is a small, calcium-binding protein and a macrophage-derived growth factor, which can promote axon regeneration in retinal ganglion cells. Oncomodulin-1 is constitutively secreted by activated macrophages in the vitreous and retina in response to inflammatory conditions that promote optic nerve regeneration. Oncomodulin-1 binds RGCs with high affinity in vitro, but only when cAMP is pharmacologically elevated or if the membrane is permeabilized allowing Oncomodulin-1 access to the cytosolic compartment. Oncomodulin-1 is a member of the superfamily of calmodulin proteins and is a high-affinity calcium ion-binding protein and contains 2 EF-hand domains. OM is found in early embryonic cells in the placenta and also in tumors. It has some calmodulin-like activity with respect to enzyme activation and growth regulation.