ATM and Telangiectasia: Based on these data, we analyzed the expression of some key cell cycle-related genes in Opn4WT and Opn4KO melanocytes: ataxia-telangiectasia-mutated (Atm) and ataxia telangiectasia and Rad3-related (Atr), which encode proteins that act on DNA damage response and are responsible for maintaining genome integrity [43].