Acts as an axon-specific repulsive guidance molecule in the retinotectal system. Repulsive for a subset of axons of the temporal half of the retina. Provides thus positional information for the temporal axons invading the optic tectum in the stratum opticum. Expressed in the periventricular layer surrounding the tectal ventricle (E9). Forms a spatial gradient with increasing concentration from the anterior to posterior pole of the embryonic optic tectum. Autocatalytically cleaved at low pH; the two chains remain linked via two disulfide bonds. Belongs to the repulsive guidance molecule (RGM) family.