Figure 2.

Process of neurogenesis. 0: ANSC in a quiescent state. 1: Type 1 cell. ANSC-activated. 2: Type 2 cell (differentiating 2a and 2b because of their phenotype). TAPC. 3: Type 3 cell. Migratory neuroblast. 4: Immature neuron. 5: Mature neuron. A. Astrocyte. The yellow arrows represent the participation of microglia in this process: microglia are able to activate latent ANSCs by the CX3C chemokine receptor (CX3CR1) in the hippocampus of mice engaged in exercise. They also participate in neurogenesis, inducing apoptosis in some type 2 cells, before the microglia phagocytize them. In addition, newborn cells have to compete with mature neurons and microglia collaborate at this point because they phagocytize weak or less active synapses. Notch1 stimulates the quiescent state, preventing the excessive activation of ANSCs. Annexin V is able to reduce apoptosis and may increase the number of apoptotic TAPCs. Migratory neuroblasts differentiate into immature neurons, which are characterized by a transient expression of calretinin.