Glial cell line-derived neurotrophic factor (GDNF) is a protein that, in humans, is encoded by the GDNF gene.[5] GDNF is a small protein that potently promotes the survival of many types of neurons.[6] It signals through GFRα receptors, particularly GFRα1. It is also responsible for the determination of spermatogonia into primary spermatocytes, i.e. it is received by RET proto-oncogene (RET) and by forming gradient with SCF it divides the spermatogonia into two cells. As the result there is retention of spermatogonia and formation of spermatocyte.[7][full citation needed]