We have identified factors downstream of Notch that mediate this function. was found to be sufficient to drive production of Mller glial cells and/or RPCs. Moreover, and were shown to partially rescue the production of bipolar and Mller glial cells in the absence of in mitotic and newly postmitotic cells. Misexpression of that influence the choice of rod and non-rod fates. Taken together, our results begin to address how different signals downstream from a common pathway lead to different fate outcomes. and after cell cycle exit, the effects of removal of a conditional allele in newly postmitotic cells were analyzed. In addition, single cell microarrays were performed to investigate gene expression changes that might lead to the acquisition of rod and non-rod fates (Mizeracka et al., 2013). Expression of and were maintained as homozygotes (Radtke et al., 1999). CD-1 mice were obtained from Charles River Laboratories. All experiments were approved by the Institutional Animal Care and Use Committee at Harvard University. Misexpression constructs CAG:Id1 and CAG:Id3 were constructed by PCR amplification from full-length mouse cDNA clones (Matsuda and Cepko, 2004). Each construct was verified by sequencing. The full-length mouse cDNA sequence encoding Nrarp was cloned into the LIA vector at the injections of DNA constructs and viruses were performed as previously described, with the exception that an oocyte microinjector (Drummond) and pulled glass pipettes (Dumont/Drummond) were used to deliver 0.2 l of 5 g/l DNA solution or 107 CFU/ml viral stock into the subretinal space of the postnatal mouse eye (Matsuda and Cepko, 2004). electroporations were performed as previously described (Matsuda and Cepko, 2004). Viruses used include LIA, LIA-Cre (Bao and Cepko, 1997; Jadhav et al., 2006), BAG (Price et al., 1987), LIA-Id1-2A-Cre and LIA-NRARP. DNA constructs used include CAG:GFP, CAG:Cre, CALNL-GFP (Matsuda and Cepko, 2004), Cralbp:dsRed, Hes1:tdTomato (Matsuda and Cepko, 2007), Chx10:tdTomato (Kim et al., 2008) and CAG:Id1, CAG:Id3. Empty vectors were added to maintain equimolar ratios among DNAs that were co-injected. Intraperitoneal injections into newborn pups were performed to deliver EdU at 1 g/l in PBS, with a total of 10 l per pup. Histology and immunohistochemistry Retinas were fixed and processed for cryosections as described previously (Matsuda and Cepko, 2004; Trimarchi et al., 2007), starting either as wholemounts (fixed for 30 minutes at 4C with 0.5% glutaraldehyde) or as eyeballs (fixed for 2 hours in 4% PFA at room temperature in PBS, pH 7.4). Primary antibodies used in this study include: chicken anti-GFP (1:2000; Abcam), rabbit anti-Chx10 (1:500; C. L. Cepkos laboratory), rabbit anti-Id3 (1:500; Abcam) and mouse anti-p27Kip1 (1:50; BD Biosciences Transduction Laboratories). EdU detection and TUNEL staining were performed according to manufacturers instructions. X-gal and alkaline phosphatase staining was performed as described previously (Bao and Cepko, 1997; Price et al., 1987). Section hybridization was performed as previously described (Trimarchi et al., 2007). Microscopy and image analysis Confocal microscopy to obtain images was performed using a Leica TCS SP5 microscope. Imaris 5.7 software (Bitplane) was used to analyze, quantify and uniformly adjust images. FACS purification and semi-quantitative PCR Electroporated retinas were dissociated to single cells via papain treatment (Trimarchi et al., 2007). FACS was performed on a BD Aria II sorter FLJ14848 or Accuri C6 Analyzer, gated for GFP and dsRed/tdTomato detection. For semi-quantitative PCR, 3-5105 GFP+ cells were collected from two dissociated retinas for each sample. After sorting, GFP+ cells were lysed in Trizol (Invitrogen) and stored at -80C. Phenol-chloroform extractions Sulfosuccinimidyl oleate were performed to isolate total RNA. cDNA was generated using Accuscript High Fidelity (Agilent Technologies) according to manufacturers guidelines. Semi-quantitative real-time PCR was performed and gene expression was normalized according to expression in each sample. Primers used included: reveals activity in newly postmitotic cells In order to determine whether Notch1 signaling plays a role in cell fate specification in newly postmitotic cells, two independent strategies were undertaken. The first Sulfosuccinimidyl oleate strategy takes advantage of the manner in which gammaretroviruses integrate the viral genome and express viral genes. Upon entering Sulfosuccinimidyl oleate a host cell, viral reverse transcriptase creates only a single copy of the viral genome in the cytoplasm. The viral DNA in the pre-integration complex of a gammaretrovirus, which is the type used for lineage tracing, cannot penetrate the nuclear envelope. Thus, integration of the viral DNA into the host genome, which allows for stable marking of a clone, can occur only after the breakdown of the nuclear envelope during M phase (Roe.