Fig. 3

Cool temperature effects in S2R+ cells on cell cycle and stress genes. (A) Temperature dependence of transcript levels of genes functionally associated with central cellular processes. Microarray data of the S2R+ cell transcriptome at the indicated temperatures was used for an analysis with curated sets of genes associated with the indicated cellular processes. (B) Enrichment of gene ontology (GO) terms by temperature-regulated genes reveal cell-type specific differences between S2R+ and HB10 cells. (C) Expression of Hsp genes is minimal at 14 °C in S2R+ cells. (D) Time course analysis of the transcriptional response to a 25- > 14 °C temperature downshift in S2R+ cells using microarrays. Culture aliquots were analyzed at the indicated times after downshift (0, 4, 12, 24 and 72 h), as well as samples maintained at 25 °C for an additional 12 h (c12). The Pearson’s correlation coefficients obtained after pairwise comparison of the different samples revealed maximal similarities between the three to five replicates from the same time point (red dashed squares). (E) Gene clusters with similar temporal expression profiles in response to a 25- > 14 °C temperature downshift identified by k-means clustering using probes with differential expression over time. Plot (top left) obtained by the elbow method [45] after analysis of clusters resulting with increasing k. Additional plots describe the clusters obtained at k = 4. Temporal profiles of signal intensities revealed steady increase and decrease in cluster 1 and 2, or transient increase and decrease in the two partially separated clusters 3 and 4. Numbers of probes assigned to the four clusters are given. (F) Temporal profile of transcript levels from genes with functional association to central cellular processes