Dissecting Signaling Pathways that Regulate Axonal Guidance Effects of Sonic Hedgehog: A Dissertation
Authors
Guo, DaorongFaculty Advisor
Zheng-Zheng Bao, Ph.D.Academic Program
Interdisciplinary Graduate ProgramDocument Type
Doctoral DissertationPublication Date
2011-03-24Keywords
Hedgehog ProteinsAxons
Intracellular Signaling Peptides and Proteins
Retinal Ganglion Cells
Amino Acids, Peptides, and Proteins
Cell and Developmental Biology
Cells
Enzymes and Coenzymes
Sense Organs
Metadata
Show full item recordAbstract
During development, axons respond to a variety of guidance cues in the environment to navigate to the proper targets. Sonic hedgehog (Shh), a classical morphogen, has been shown to function as a guidance factor that directly acts on the growth cones of various types of axons. We previously found that Shh affects retinal ganglion cell (RGC) axonal growth and navigation in a concentration-dependent manner. However, the signaling pathways that mediate such events are still unclear. In this thesis, we show that high concentrations of Shh induce growth cone collapse and repulsive turning of the chick RGC through rapid increase of Ca2+ in the growth cone, and specific activation of PKCα and Rho signaling pathways. We further found that integrin linked kinase (ILK) acts as an immediate downstream effector of PKCα. PKCα directly phosphorylates ILK in vitro at two previously unidentified sites threonine-173 and -181. Inhibition of PKCα, Rho, and ILK by pharmacological inhibitors and/or dominant-negative approaches abolished the negative effects of high-concentration of Shh. We provide evidence that Rho likely functions downstream of PKC and suggest that PKC, Rho and ILK may cooperatively mediate the negative effects of high concentrations of Shh. Furthermore, retroviral expression of dominant-negative constructs of PKCα (DN-PKCα) and ILK-double mutants (ILK-DM) resulted in misguidance of RGC axons at the optic chiasm in vivo. These results demonstrate that new signaling pathways composed of PKCα, Rho, and ILK play an important role in Shh-induced axonal chemorepulsion. In contrast, we show that attractive axonal turning in response to low concentrations of Shh is independent of PKCα, but requires the activity of cyclic nucleotides cAMP. Taken together, our results suggest that the opposing effects of Shh on axon guidance are mediated by different signaling pathways.DOI
10.13028/hdbp-f309Permanent Link to this Item
http://hdl.handle.net/20.500.14038/31870Rights
Copyright is held by the author, with all rights reserved.ae974a485f413a2113503eed53cd6c53
10.13028/hdbp-f309