Retroviral stock preparation

We used a retroviral stock encoding for Venus fluorescent protein on an RSF91 backbone (Schambach et al., 2006; Gomez-Nicola et al., 2014). The plasmids used to produce the virus were kindly provided by Prof. Miyawaki (RIKEN Brain Science Institute), Dr. Riecken (University Medical Center Hamburg-Eppendorf), and Dr. Gage (Salk Institute). Retroviral stocks were concentrated to working titers of 1 × 10⁷ to 1 × 10⁸ pfu/ml by ultracentrifugation (Zhao et al., 2006). Because the retroviruses used are engineered to be replication-incompetent, only cells dividing at the time of surgery are infected (Zhao et al., 2006). In the DG, these proliferative cells are almost totally restricted to newborn DGCs (Zhao et al., 2006).