Fig. 2. Cellular information processing.

(A) The expression of String protein signals cells to enter mitosis 14 at the onset of Drosophila gastrulation. Here is a graphical illustration of the noise present in String concentration over time. (B) Cells can interpret or “process” the concentration of String (as an input) in myriad ways. We provide a schematic of just three simple tactics of information processing. Cells can respond to a particular threshold concentration of String at a particular time, or cells can use an integration-type method, whereby the concentration of String is integrated over the whole history or a particular time interval. (C) The output generated by each processing strategy is shown. The ouput generated by the instantaneous method is subject to any noise present in the input. The integration method is able to smoothen noise, but in doing so, generates a sluggish response, which loses the abrupt change in String concentration. The short-term integration method is superior for making a decision which is both quick and accurate, because it filters noise while maintaining the abrupt change in String concentration. (D) A diagram of the covalent modification cycle between Wee1, String, and Cdk1 is provided. A linear influx of String overcomes the constant concentration of Wee1. Under certain paramters this is enough to trigger an ultrasensitive response.