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. Author manuscript; available in PMC: 2022 Aug 9.
Published in final edited form as: Nat Cell Biol. 2020 Jan 6;22(1):74–86. doi: 10.1038/s41556-019-0441-z

Figure 5. Mathematical prediction of PC-I and collagen I secretion.

Figure 5

(A) Phase portrait showing relationship between intracellular collagen concentration and extracellular collagen concentration over a 24-hour cycle. Black star shows CT0, and the line colour shows the circadian time increasing in the direction indicated by the arrows. The pink star indicates stationary concentration values for the model when the circadian forcing functions are removed. (B) 48-hour time plot (CT0 to CT48) of intracellular (purple) and extracellular (blue) collagen concentration fluctuations as predicted by mathematical modelling. (C) Still frame from a video representation (Supplementary Video 5) of a mathematical model of the secretory pathway showing PC-I levels in ER (SEC61-dependent translation of PC-I into ER, pCER(t)), ER exit sites (TANGO1-dependent PC-I export from ER, pCH(t)), Golgi (PDE4D-dependent transport, pCG(t)), post-Golgi (VPS33B-dependent transport, pCPG(t)), plasma membrane (pCPM(t)), and extracellular matrix (CSTK-dependent collagen degradation, pCE(t)). Bar height represents collagen concentration, and colour represents the rate of change of concentration (blue - low to red - high). The paired bars represent collagen levels at CT3 and CT15.