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Growth cones integrate signaling from multiple guidance cues
Vassil D Dontchev1, Paul C Letourneau
1Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Summary
Nerve growth factor (NGF) and semaphorin3A (Sema3A) guide developing neurons. NGF can override Sema3A repulsion, and prior NGF exposure enhances neuronal resistance to Sema3A, revealing complex guidance cue interactions.
Area of Science:
- Neuroscience
- Developmental Biology
- Cell Biology
Background:
- Developing neurons utilize guidance cues like Nerve Growth Factor (NGF) and Semaphorin 3A (Sema3A) for pathfinding.
- Dorsal Root Ganglia (DRG) neuron growth cone motility is dynamically regulated by intracellular signaling pathways activated by these cues.
Purpose of the Study:
- To investigate the interactive effects of NGF and Sema3A on the growth cone behaviors of developing chick embryo DRG neurons.
- To elucidate the signaling mechanisms underlying the modulation of growth cone responses to guidance cues.
Main Methods:
- Culturing E7 chick embryo DRG neurons in collagen matrices.
- Utilizing transfected HEK293 cells to present Sema3A and NGF-coated beads as localized guidance cues.
- Employing pharmacological inhibitors to probe the roles of specific signaling pathways (ROCK, PKG, PKA).
Main Results:
- Sema3A induced repulsion of DRG axons, while NGF attracted them, demonstrating opposing guidance.
- Pre-exposure to higher concentrations of NGF (10(-9) M) increased growth cone resistance to Sema3A-induced collapse.
- NGF treatment enhanced resistance to Sema3A-induced collapse, mediated by PKA activity, while ROCK and PKG pathways were involved in Sema3A-induced collapse.
Conclusions:
- Growth cone responses to guidance cues are not isolated but are significantly modulated by the presence and signaling of other cues.
- NGF can counteract Sema3A-mediated repulsion, suggesting a hierarchical or interactive signaling mechanism in neuronal pathfinding.
- Specific intracellular signaling pathways (PKA, ROCK, PKG) differentially mediate the effects of NGF and Sema3A on growth cone cytoskeletal dynamics.