The initial appearance of the RMS marked the

beginning of the analysis. The cell density of the total RMS of each half brain was calculated from every fifth section. The cell densities were then summed and divided by total sections that were measured to arrive at the mean density. Total cell number was calculated for the entire RMS using the density and volume measurements. The total cell number was a rough estimate because these counts are inflated due to the inclusion of double cell counts. QTL mapping was performed using WebQTL, a module of the GeneNetwork (http://www.genetwork.org) which is an open-access online database Belnacasan that contains detailed genotype information of the RI strains generated from 8514 informative markers. WebQTL implements both simple and composite interval mapping methods described by Knott et al. (2002), and

also scans the genome for non-linear, epistatic interactions among two or more loci. The likelihood ratio statistic (LRS) was computed to assess genotype–phenotype associations and to determine QTL. Genome-wide significance levels for assessing the confidence of the linkage statistics were estimated by comparing the peak LRS of correctly ordered data sets with LRSs computed for 1000 permutations (Churchill & Doerge, 1994). Permutation tests are a widely accepted method for determining the probability of the association occurring by chance. The LRS score can be converted to a likelihood of the odds (LOD) score by dividing by 4.61, and

we used the conventional 2.0 LOD drop-off Ixazomib chemical structure interval to define the confidence limits of QTL peaks as recommended by Manichaikul et al. (2006). AXBXA RI genotypes and marker distribution patterns are downloadable at http://www.genenetwork.org/dbdoc/AXBXAGeno.html. Phenotypic data on the BrdU-labeled cells in the RMS and SGZ for the AXB/BXA lines have been deposited in GeneNetwork (Trait ID # 10124 and 10125). We used three complementary approaches to identify candidate genes in the QTL region that modulate the number of proliferative cells in the RMS: (1) genes were assessed as to their involvement in neurogenesis, cell proliferation and cell cycle using the ontological information provided by Entrez Gene (NCBI; http://www.ncbi.nlm.nih.gov) and Mouse Genome Informatics (MGI; http://www.informatics.jax.org); however (2) the Allen Brain Atlas (ABA; http://www.brainatlas.org) was used to examine the expression pattern of each gene in the adult mouse brain; (3) we also investigated whether our list of genes were involved in any signaling pathways that were known to regulate adult neurogenesis. We carried out our assessment by first creating a list of 30 targeted genes that were key components of known pathways described in supplementary Table S1. We then submitted both the targeted genes and the QTL genes to the Database for Annotation, Visualization and Integrated Discovery (DAVID; http://david.abcc.ncifcrf.gov/summary.