GPR17 and neoplasm: O1 tumours were characterized by a higher expression of oligodendrocyte precursor cell (OPC) markers, especially GPR17 (ref. 11) and CCND1 (ref. 12) which was validated by immunohistochemistry (Fig. 3b); O2 tumours strongly overexpressed neuron markers13, 14 and genes implicated in neurogenesis; and O3 tumours specifically expressed mature oligodendrocyte markers14, 15.