PCGF1 and glioblastoma: The epigenetic modification of the nervous system polycomb1 (NSPc1) gene was found to suppress the expression of retinol dehydrogenase-16 (RDH16), the enzyme that converts retinol to all-trans retinoic acid (ATRA) in GBM cells, resulted in the decreased synthesis of intracellular ATRA, which impeded cell differentiation and promoted development of stem-like cells (SLC) [19].