Given the phenotypic similarities between suppression of DISC1 and PTEN in dentate granule cells of the adult brain (Duan et al., 2007; Kwon et al., 2006), we examined AKT signaling in newborn neurons with antibodies raised specifically against phosphorylated AKT (pAKT at Ser473), a marker of AKT activation (Manning and Cantley, 2007). We have previously developed a specific shRNA against mouse disc1 (DISC1-shRNA) and confirmed its efficacy and specificity in knocking down endogenous DISC1 in hippocampal neurons in vitro (See Figure S1 in the Supplementary Data)(Faulkner et al., 2008) and in dentate granule cells in vivo (Duan et al., 2007). We stereotaxically injected engineered retroviruses co-expressing GFP and DISC1-shRNA, or a control-shRNA, into the dentate gyrus of the adult mouse hippocampus (See Experimental Procedures). This “single-cell genetic” approach allows birth-dating, lineage tracing and genetic manipulation of proliferating neural progenitors in a cell autonomous fashion in the adult brain (Ge et al., 2006). Immunostaining of pAKT and DCX, an immature neuronal marker, showed a significant increase of pAKT in GFP+DCX+ new neurons expressing DISC1-shRNA, but not control-shRNA, at 14 days post
