DTNBP1 (dystrobrevin-binding protein 1) which encodes dysbindin-1 is one of the leading susceptibility genes for schizophrenia. Both dysbindin-1B and 1C isoforms are decreased but the 1A isoform is unchanged in schizophrenic hippocampal formation, suggesting dysbindin-1 isoforms may have distinct roles in schizophrenia. We found that mouse dysbindin-1C, but not 1A, is localized in the hilar glutamatergic mossy cells of the dentate gyrus. The maturation rate of newborn neurons in sandy (sdy) mice, in which both dysbindin-1A and 1C are deleted, is significantly delayed when compared with that in wild-type mice, or with that in muted (mu) mice in which dysbindin-1A is destabilized but 1C is unaltered. Dysbindin-1C deficiency leads to a decrease in mossy cells, which causes the delayed maturation of newborn neurons. This suggests that dysbindin-1C, rather than 1A, regulates adult hippocampal neurogenesis in a non-cell autonomous manner.