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dc.contributor.authorManns, Richard Peter Charles
dc.date.accessioned2014-08-20T10:52:10Z
dc.date.available2014-08-20T10:52:10Z
dc.date.issued2013-01-08
dc.identifier.otherPhD.35945
dc.identifier.urihttps://www.repository.cam.ac.uk/handle/1810/245741
dc.description.abstractThe aim of the work described in this thesis is to investigate the nature and mechanisms of action of repellent cues for growing axons. In particular I try to resolve the controversy in the literature regarding the need for protein synthesis in the growth cone in response to external guidance cues. My results resolve the conflicting data in the literature on Semaphorin-3A signalling, where differing labs had shown that inhibiting protein synthesis either blocks or has no effect upon repulsion. They demonstrate the presence of at least two independent pathways, protein synthesisdependent mTOR activation and -independent GSK3β activation. The higher sensitivity of the synthesis-dependent pathway, and its redundancy at higher concentrations where synthesisindependent mechanisms can evoke a full collapse response alone, resolve the apparent conflict. My experiments also demonstrated that Nogo-δ20, a domain of Nogo-A, requires local protein synthesis to cause collapse. Unlike Semaphorin-3A, the dependence of collapse upon protein synthesis is concentration-independent and does not involve guanylyl cyclase, but it does share a dependence upon mTOR activity and the synthesis of RhoA, sufficient to cause collapse downstream of Semaphorin-3A. The other axon-repelling domain of Nogo-A, Nogo-66, is partially dependent upon the proteasome instead. It does not share a common pathway with Nogo-δ20, except that both are RhoA-dependent. I further attempted to identify the nature of a repulsive activity found in grey matter, ruling out a previously suggested candidate identity. Finally, I examined the phenomenon of nitric oxide-induced growth cone collapse. My experiments revealed that S-nitrosylated glutathione causes growth cone collapse through the activity of protein disulphide isomerase. This mechanism shows only a partial dependence upon soluble guanylyl cyclase, but I argue that it has total dependence upon an S-nitrosylated donor. Coupled with its apparent relation to Spalmitoylation, the reciprocal of S-nitrosylation, I propose that nitric oxide causes collapse by crossing the cell membrane to inhibit S-palmitoylation–determined localisation of proteins. These results reveal some of the many pathways involved in growth cone collapse, whose further characterisation may provide new targets for the treatment of injuries of the central nervous system.
dc.subjectaxon repulsionen
dc.subjectaxon guidanceen
dc.subjectneuronen
dc.subjectglial scaren
dc.subjectastrocyteen
dc.subjectgliosisen
dc.subjectspinal corden
dc.subjectprosaposinen
dc.subjectnitrosylationen
dc.subjectdorsal root ganglionen
dc.subjectSemaphorin-3Aen
dc.subjectastrogliomaen
dc.subjectrapamycinen
dc.subjectmTORen
dc.subjectNogo-66en
dc.subjectamino-Nogoen
dc.subjectNogo-Aen
dc.subjectreticulon-4Aen
dc.subjectnitric oxideen
dc.subjectcGMPen
dc.subjectproteasomeen
dc.subjectconcentration dependenceen
dc.subjectgrowth coneen
dc.subjectquantitative immunofluorescenceen
dc.subjectprotein disulphide isomeraseen
dc.subjectprotein disulfide isomeraseen
dc.titleRepulsive cues and signalling cascades of the axon growth coneen
dc.typeThesisen
dc.type.qualificationlevelDoctoral
dc.type.qualificationnameDoctor of Philosophy (PhD)
dc.publisher.institutionUniversity of Cambridgeen
dc.publisher.departmentDepartment of Physiology, Development and Neuroscienceen
dc.identifier.doi10.17863/CAM.16341
rioxxterms.freetoread.startdate2017-01-08


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