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Activation of the p42 pathway is irreversible unless the Mos positive feedback loop is blocked (right three lanes). Ferrell/Macmillan

Asimple positive feedback loop is a memory aid for egg cells that pushes their metabolism in one direction, based on research from Wen Xiong and James Ferrell (Stanford University, Stanford, CA). According to Ferrell, the work puts "some biochemical meat on the bones of commitment."

That commitment occurs during egg cell maturation. Frog egg cells mature from a paused G2-like state in response to a hormone stimulus. Even a transient stimulus pushes cells through maturation to meiosis II via a kinase/phosphatase cascade of 15 proteins, including p42 MAPK, cyclin B/Cdc2, and Cdc25. As phosphorylation is reversible but maturation is not, cells must somehow remember their hormone encounter. The authors now show that this memory lies in a positive feedback loop in the p42 pathway.

Feedback is provided by the protein Mos, which activates p42, which in turn promotes Mos accumulation. By blocking the effects of Mos, the authors show that p42 MAPK activation becomes reversible in the absence of positive feedback. The simplicity of positive feedback loops explains why researchers stumble upon them so often, according to Ferrell, who hopes "clever systems biologists will uncover other examples [of] irreversible cell fates established by positive feedback loops."

Reference:

Xiong, W., and J.E. Ferrell. 2003. Nature. 426:460–465.[CrossRef][Medline]

Nicole LeBrasseur

lebrasn{at}rockefeller.edu

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This Article PDF (Full Text) PPT slides of all figures Alert me when this article is cited Services Email this article Similar articles in this journal Alert me to new content in the JCB Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by LeBrasseur, N. Search for Related Content PubMed Articles by LeBrasseur, N. Social Bookmarking                      What's this?