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. Author manuscript; available in PMC: 2012 Apr 19.
Published in final edited form as: Sci Signal. 2010 Apr 20;3(118):jc1. doi: 10.1126/scisignal.3118jc1

Fig. 1.

Fig. 1

cAMP signals regulate competitive neurite outgrowth. (A-C) Competitive outgrowth of neurites during axon specification. (A) A postmigratory neuron with several undifferentiated neurites. One of these stochastically exhibits higher cAMP concentrations (top). (B) The neurite with high cAMP concentrations reinforces its own cAMP signaling through positive feedback and reduces cAMP concentrations in the other neurites through long-range signaling. (C) Higher cAMP concentrations stimulate growth of the top neurite (which becomes the axon) while suppressing cAMP, and therefore the growth, of the others. (D-F) Proposed model for the competitive outgrowth of primary axons vs. branches regulated by cAMP signaling. (D) An axon branch stochastically exhibits higher cAMP concentrations than the primary axon. (E, F) As cAMP concentrations rise in the branch through positive feedback, cAMP concentrations in the primary axon are reduced by long-range signaling. This causes the branch to extend rapidly while reducing the growth of the primary axon.