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.

No description available.

published_or_final_version / Anatomy / Doctoral / Doctor of Philosophy

The function of CABP1, a novel cAMP-binding protein in Dictyostelium discoideum, has been investigated. Previously, it has been shown that the molecular weight of CABP1 varies in different strains and that this variation is correlated with differences in response to cAMP. Sequence analysis showed that compared to its counterpart in strain AX2, the gene encoding CABP1 of strain V12M2 is missing 27 bp. AX2 transformants expressing the capA gene of V12M2 exhibited no change in phenotype, suggesting that CABP1 is not involved in the features examined or that the V12M2 variant is recessive. Disruption of capA by homologous recombination was attempted with no success, suggesting that this gene might be essential. Proteins interacting with CABP1 have been identified by immunoprecipitation using specific antibodies, CABP1 was also found to copurify with annexin VII, a calcium-dependent phospholipid-binding protein, suggesting that CABP1 and annexin VII might interact.

Thesis (M. Phil.)--University of Hong Kong, 2007. / Also available in print.

Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xxiv, 256 p.; also includes graphics (some col.). Includes bibliographical references (p. 228-256).

Thesis (Ph. D.)--University of Hong Kong, 1996. / Includes bibliographical references (leaf 173-194).

Thesis (M.Sc.)--Memorial University of Newfoundland, 2002. / Restricted until May 2003. Bibliography: leaves 138-144.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1971. / Typescript. Vita. Description based on print version record. Includes bibliographical references (leaves 92-107).

Immobilized boronates were evaluated for studies of adenine nucleotide metabolism. These studies were performed using Affi-gel 601, a commercial boronate gel, and dihydroxyboryl Sepharose and dihydroxyboryl-Bio Rex which were synthesized in the laboratory. The studies performed included the determination of the relative binding affinity of a variety of adenine containing compounds for the three immobilized boronates under differing chromatographic conditions.