MKNK1 and major depressive disorder: To study the role of eIF4E phosphorylation in depression pathophysiology, we examined the Mnk1 and Mnk2 double knock-out (Mnk1/2−/−)11, and the Eif4e Ser209Ala knock-in (Eif4e ki/ki)12 mice in several validated paradigms for depression-like behavior.