GFAP and neoplasm: To further clarify these differences and understand why in some instances the oncogene HRASV12 expressed in brain progenitor cells induced tumour development and in other cases produced only heterotopias, we investigated the expression of different markers by immunofluorescence: BrdU uptake for proliferation, GFAP for glial cells, S100β for progenitor cells, HU-C for neurons and p-ERK for MAPK activity.