Oscillating dCREB2 and NF-kB Activity Figure 3. dCREB2 and NF-kB activity cycle in multiple tissues. Reporter activity is plotted as a function of circadian time. Each different cellular population is described on the left, and the tissue-specific driver used to activate the reporter is shown. In each panel, a comparison is shown between the background (denoted no driver) and activated (driver) expression levels. The activity is shown for the CRE-F-luc (panels A–C) and the NFkB-F-luc (panels E–G) reporters in neurons (panels A and E), glia (panels B and F) and in the mushroom body (panels C and G). The average activity over the duration of the experiment for each driver is quantified for the CRE-F-luc (panel D) and NFkB-F-luc (panel H) reporters. All bars represent mean hourly counts from 24–28 flies. Error bars = S.E.M, ***p,0.001, **** p,0.0001. doi:10.1371/journal.pone.0045130.g003 CRE-F-luc reporter is expressed in certain small clusters of cells, activity cannot be measured, precluding us from concluding that dCREB2 activity cycles everywhere in the adult head (Table S1). However, since most major cell types and anatomical structures show oscillatory activity (Fig. 3A–D, Table S1), we suspect that dCREB2’s activity oscillates ubiquitously. This suggests that the experimentally observed oscillating activity does not result from the activity of certain cells dominating the measured signal. Instead, the general diurnal pattern seems to occur when the reporter is activated in most, if not all, cells. The NF-kB transcription factor reporter also oscillates, and is directly or indirectly under the control of the circadian system (Fig. 2B, 3E–H, 4). The Drosophila genome encodes three NF-kB family members, characterized by a conserved DNA binding domain: Dorsal, DIF (dorsal-related immunity factor) and Relish. These proteins can form homodimers or heterodimers to regulate PLOS ONE | www.plosone.org 5 October 2012 | Volume 7 | Issue 10 | e45130