A functional context for heterogeneity of the circadian clock in cells
Fig 2
A concept of entrained phase from the level of populations of cells.
The curves shown in this figure represent entrained phase to times within the first 6 h of a day (horizontal axis). Apparently, homogeneous cells exhibit a range of free-running periods and therefore a range of entrained phases (left panel, each putative cell line scaled to an amplitude of 1). The center panel depicts the same collection of curves but with the vertical axis scaled proportionally to the panel on the right, which shows a summation of the individual profiles shown to the left. This simply derived additive curve resembles, e.g., bioluminescence profiles showing clock regulated gene expression, such as shown in Nikhil and colleagues [4]. Actual expression curves should vary according to what is quantified—they could be broader or narrower depending on what is measured and on the distribution of component entrained phases.