HFPNe model and its simulation result of circadian rhythm in Drosophila. (a) HFPNe model of circadian rhythm in Drosophila. The accompanying variable m
at a place represents the concentration of the corresponding mRNA, protein or the compound. For example, the variable m1 indicates the concentration of dClk mRNA. Reaction speed (the rate of transcription, translation, complex formation or degradation) is expressed by a simple formula at each transition. For example, the formula m1/5 indicates the translation rate of dCLK protein that depends on the variable m1 for the dClk Mrna concentration. The real number over an arc is the threshold for the content of the place attached to this arc. For example, the translation of tim mRNA occurs during the period that the place value of tim mRNA exceeds 1.0. (b) Oscillations of tim, per, dClk mRNAs, and the proteins TIM, PER, dCLK, PER/TIM, PER/DBT, dCLK/CYC (left y-axis) and DBT, CYC (right y-axis). The unit of x-axis is [pt] ([pt] is the virtual time unit of the HFPNe model), while that of y-axis is [vc] ([vc] is the virtual concentration unit).