Fig. 1.

Adult neurogenesis in physiological state and mechanisms of cell cycle reentry of post-mitotic neurons in AD. This fig depicts the flowchart describing neurogenic process and the cell cycle reentry of post-mitotic neurons in association with Wnt signaling in healthy and AD conditions. In the normal brain, expression of CDK4 maintains the post-mitotic neurons at the G0 cell cycle phase whereas in the pathogenic process of AD the elevated expression of cyclin D, Cyclin B, and PCNA and downregulation of CDK4 results in the cell cycle reentry of post-mitotic neurons resulting in reactive neuroblastosis through the activation of Wnt signaling. Further, the activation of p53 in neurons can lead to apoptosis accounting for neurodegeneration in AD.