| Summary: | 碩士 === 國立陽明大學 === 生命科學系暨基因體科學研究所 === 100 === Rab belongs to the superfamily of Ras small G protein. Rab proteins serve as membrane trafficking coordinators in eukaryotic cells. Rab18, a ubiquitously present protein, has been reported to participate in lipid metabolism, Golgi-ER trafficking and secretory activity in different cell types. However, the physiological role of Rab18 is unclear. The Rab18-deficient mice showed severe hind limbs ataxia and reduced size in cerebellum. At the cellular level, in Rab18-deficient mice, the dendritic arbors of Purkinje cells were disrupted in young (2 weeks) mice, the granule cells were retained in the external cerebellum, and the number of interneurons also decreased. It appears that Rab18 affects cerebellum development. The mouse cerebellum primary culture system enriched with Purkinje cells was then established. When Purkinje cells were co-cultured with cerebellar cells, the Purkinje cells showed more complex dendrites. To study the molecular mechanism of Rab18, Rab18 mutants, including constitutively active GTP-bound (Q67L), and dominant negative GDP-bound (S22N), prenylation site mutated (CSC) mutants, were constructed. By using total internal reflection fluorescent microscopy, we found the GTP-bound constitutively active mutant, Rab18-Q67L, inhibited the NPY-EGFP secretion in PC12 cells. When Rab18 and another well-studied Rab protein, Rab3A, which inhibited the secretory activity by acting as a gatekeeper for exocytosis, were co-expressed in PC12 cells, the two proteins were found to localize different population of vesicles. The results suggest that Rab18 involves in secretory pathway but may act at different population of vesicles from that affected by Rab3A.
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