Our investigation suggests that Epac, and not the canonical PKA, is the main effector involved in cAMP-mediated axon growth and guidance, and that the MAPK regulator, B-Raf, can be differentially regulated by both Epac and PKA. Direct activation of Epac induces activation of B-Raf, whereas activation of PKA results in inhibition. Moreover, in embryonic neurons, Epac-B-Raf signalling was found to be activated by the cAMP-dependent guidance molecule Netrin-1 (attractive to developing axons) and by cAMP activity at all levels tested, whereas in adult neurons, PKA signalling was activated by Netrin-1 (repulsive to adult neurons) and low levels of cAMP activity. When cAMP was substantially elevated in adult neurons, Epac-B-Raf signalling was induced, and the response of adult axons to Netrin-1 was switched from repulsion to attraction, indicating B-Raf activity is consistent with chemoattractive axon turning. Furthermore, B-Raf activity was found to localise towards the leading edge of a turning growth cone when visualised with fluorescent microscopy. Neurons lacking B-Raf protein were unable to respond to cAMP-dependent guidance cues and postnatal neurons no longer responded to artificial cAMP elevation, which usually induces an increase in axon outgrowth. Calcium influx into growth cones usually induced by axon guidance cues and cAMP activators, were also attenuated in neurons lacking B-Raf. These data suggest B-Raf is a vital effector for cAMP-mediated axon growth and guidance.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:540466 |
| Date | January 2010 |
| Creators | Peace, Andrew G. |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=166172 |
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