PCNA and Alzheimer disease: A series of studies have shown ectopic expression of stem cell / cell cycle markers, such as Sox2, PCNA, and Ki-67, in mature postmitotic neurons, including granule cells (GCs), in the hippocampal DG in the brains of patients with AD and other neurodegenerative disorders [4, 5] (for references, see Additional file 1: Table S2).