CLOCK and glioblastoma: Unlike differentiated GBM cells and non-malignant brain cultures that showed potent circadian rhythms, GSCs displayed intense dependence on core clock transcription factors, BMAL1, and CLOCK for optimal cell growth where induction of cell cycle arrest and apoptosis followed BMAL1 or CLOCK downregulation (138), a modest anti-proliferative effect was observed upon knockdown of NPAS2, indicating a non-redundant function in GSCs.