Cheng, Tat Cheung. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 181-188). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

The main focus of my PhD studies was aimed at understanding the general mechanism of nuclear translocation and isolating novel components of the nuclear translocation pathway in neurons. Using the Drosophila visual system as an in vivo model to study nuclear motility in developing photoreceptor cells (R-cells), I have identified a novel role for the Ser/Thr kinase Misshapen (Msn) and the endocytic trafficking pathway in regulating the nuclear translocation process. / The development of R-cells in the Drosophila eye disc is an excellent model system for the study of nuclear motility owing to its monolayer organization and the stereotypical translocation of its differentiating R-cell nuclei along the apical-basal plane. Prior to my thesis work, several laboratories had identified dynein and its associating proteins in R-cell nuclear translocation, however nothing was known about the signalling pathway that controlled their function in nuclear migration. Thus, one of my thesis goals was to elucidate the signalling mechanism controlling nuclear translocation in R-cells. / Using a combination of molecular and genetic approaches, I identified Msn as a key component of a novel signalling pathway regulating R-cell nuclear translocation. Loss of msn causes a failure of R-cell nuclei to migrate apically. Msn appears to control R-cell nuclear translocation by regulating the localization of dynein and Bicaudal-D (Bic-D). My results also show that Msn enhances Bic-D phosphorylation in cultured cells, suggesting that Msn regulates R-cell nuclear migration by modulating the phosphorylation state of Bic-D. Consistently, my results show that a Bic-D-phosphorylation-defective mutation disrupted the apical localization of both Bic-D and dynein. I propose a model in which Msn induces the phosphorylation of Bic-D, which in turn modulates the activity and/or subcellular localization of dynein leading to the apical migration of R-cell nuclei. / In addition to studying Msn, I have also searched for additional players in R-cell nuclear migration. From a gain-of-function approach, I found that the misexpression of the GTPase-activating-protein (GAP) RN-Tre caused a severe defect in R-cell nuclear migration. Since mammalian RN-Tre is involved in negatively regulating Rab protein activity, I speculated that the RN-Tre misexpression phenotype reflected a role for Rab-mediated vesicular transport in regulating R-cell nuclear migration. I systematically examined the potential role of Rab family proteins in R-cell nuclear migration and found that interfering with the function of Rab5, Rab11 or Shibire caused a similar nuclear migration phenotype. I propose that an endocytic pathway involving these GTPases is required for the targeting of determinants to specific subcellular locations, which in turn drive the apical migration of R-cell nuclei during development.

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