PCNA and Alzheimer disease: Despite these indications of a reactivation of cell cycle processes in cerebellar dentate nuclei of the AD brain, we found that there was no significant difference (p = 1.0, Table 1) between AD and controls in the number of dentate nuclei immunoreactive for PCNA (proliferating cell nuclear antigen), a component of the DNA replication complex that is elevated during S-phase.