Normal Limits

"Chance is the very guide of life"

"In practical medicine the facts are far too few for them to enter into the calculus of probabilities... in applied medicine we are always concerned with the individual" -- S. D. Poisson

October 22, 2005

Science - [REPORTS] Interlinked Fast and Slow Positive Feedback Loops Drive Reliable Cell Decisions

"Many cell signaling networks consist of dual feedback loops, enabling them to combine rapid response with reliable performance.Authors: Onn Brandman, James E. Ferrell Jr., Rong Li, Tobias Meyer"

Positive feedback is a ubiquitous signal transduction motif that allows systems to convert graded inputs into decisive, all-or-none outputs. Here we investigate why the positive feedback switches that regulate polarization of budding yeast, calcium signaling, Xenopus oocyte maturation, and various other processes use multiple interlinked loops rather than single positive feedback loops. Mathematical simulations revealed that linking fast and slow positive feedback loops creates a "dual-time" switch that is both rapidly inducible and resistant to noise in the upstream signaling system.

Of interest are platelet activation and coagulation cascade activation (E Beltrami and J Jesty 1995).

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