For specific analysis of single genes, the fifty most prominently transcriptionally altered genes were evaluated by real time PCR. Mouse code based primers worked reproducibly and specifically for 35 genes. Among them, 21 genes were found to be differentially transcribed with enhanced c-secretase activity ( Fig. 3 upper panel, annotations lower panel). The highest increase in transcription Categories within the Molecular Function GO hierarchy that were over-and under-represented among the genes that were differentially transcribed in cells with enhanced c-secretase activity. Red boxes display GO terms that were overrepresented; blue boxes indicate GO terms that were under-represented. Black boxes represent main molecular functional clusters and arrows point toward according subclusters. The clustering of 1981 differentially transcribed genes was performed with DAVID and the FatiGo tool [23] . doi:10.1371/journal.pone.0006952.g002 levels was detected for UPP1, a gene encoding an enzyme (Uridine phosphorylase, UPase) directly implicated in the processing of uridine. UPP1 was confirmed by real time PCR to have a 39.2-fold increase in transcription levels ( Fig. 3 upper panel). Uridine is a strong sleep-promoter and is crucial for RNA, DNA and membrane biosynthesis [31] . Because of the latter, a lack of uridine (caused by increased UPase) would thus first damage cells with a large membrane to cytoplasm ratio, one of the most extreme ratios being found in neurons due to their axon and dendrite structure [32] . Interestingly oral administration of uridine has improved AD phenotypes [33, 34] . The protein Upp1 also interacts with Vimentin [35] , the distribution of which is characteristically altered in FAD fibroblasts [36] .