GFAP and neoplasm: To test whether tumor-associated astrocytes could be a source of DLK1 in the glioma tumor microenvironment, we generated PDGFB/shp53-induced murine gliomas using the RCAS/tv-a system as previously described [14], then co-stained tumors for the astrocyte marker glial fibrillary acidic protein (GFAP) and DLK1.