DISC1 and major depressive disorder: In distinction from DN-DISC1 mice, N-ethyl-N-nitrosourea (ENU) was used to induce mutations in exon 2 of mouse Disc1 gene, resulting in the occurrence of missense mutations such as Q31L (glutamine to leucine) or L100P (leucine to proline), causing an increase in depression-like behaviors in Q31L mice and schizophrenia-like behaviors including impaired prepulse inhibition (PPI) and latent inhibition in L100P mice (Clapcote et al., 2007; Shoji et al., 2012).