Fig. 8. Model of ATM-Chk2-p53 pathway in zebrafish retinal neurogenesis. In the zebrafish retina, mitotic progenitor cells start to generate neurons at 24 hpf. After 24 hpf, the cell cycle duration of retinal progenitor cells shortens and the cell proliferation rate increases. The increase in cell proliferation rate may increase the number of DNA replication errors during retinal neurogenesis. One possible model is that the ATM-Chk2-p53 pathway repairs the replication errors or induces apoptosis to remove retinal neurons with unrepaired DNA damage. This pathway might prevent the accumulation of abnormally differentiated neurons, which possibly compromise the subsequent formation of neural circuits, and might also remove cancer-predisposing cells.