Fig. 7. A mathematical model to describe and predict daily protein O-GlcNAcylation rhythm based on molecular clock function and timing of food intake.

a Schematic model showing the regulation of protein O-GlcNAcylation by the circadian clock through feeding activity and post-transcriptional mechanism(s). Yellow background indicates feeding period while the blue background indicates fasting period. Red arrows denote activation, and the thicker red arrows denote a stronger effect. b–f Line graphs showing daily rhythms of (b) GFAT activity, (c) UDP-GlcNAc, (d) OGT protein, (e) OGA protein and (f) protein O-GlcNAcylation levels as predicted using the mathematical model (Table 1). In (e), the predicted OGA protein levels are the same in WT RF9-15 and per⁰ RF21-3 flies, and the two curves overlap in the graph. Therefore, a dashed line is used to indicate OGA level in WT RF9-15 group. Time of feeding for WT RF21-3, WT RF9-15 and per⁰ RF21-3 fly groups were used as input for the model and the circadian clock is assumed to be functional in WT but not in per⁰ flies. Gray shading in graph area indicates the dark period of LD cycle. Colored bars at the top of graphs denote the feeding periods for TRF treatment groups, RF21-3 (blue) and RF9-15 (yellow).