| Summary: | 博士 === 國立清華大學 === 分子醫學研究所 === 103 === Axonal growth cones are the tips of axons responsible for exploring environment, growth of axons, guiding axons to move toward their targets. Local protein synthesis and cytoskeleton reorganization are rapidly executed when growth cones response to guidance cues. Here, we investigated transcripts residing in growth cones and their distributions to understand the roles played by local protein synthesis on axonal growth. We developed a chip devise for separately collecting growth cones and axonal shafts. We identified cone-preferred transcripts by quantitation and classification of transcripts found in axonal shaft and growth cones. By means of fluorescence in situ hybridization, we found that growing conditions affected cone-preferred distributions of Nefl and Cfl1 but not the distribution of Cadm1. Furthermore, we found that the fraction of cone-preferred distributions of Cadm1 and Nefl increased during in vitro development. Our results suggest the distributions of transcripts over axonal substructures were dynamical regulated by growing conditions and neuronal maturation.
We also investigated the differential roles played by the two microtubule-associated protein tau isoforms, which differed in their binding ability to microtubules, in the axonal growth cones. By means of fluorescence immunostaining, we found that 3R- and 4R-tau proteins were randomly enriched in several growth cones during the early stage of in vitro development. After axon determination, we found that 3R- and 4R-tau proteins were enriched in axonal growth cones. We also found that the enrichments of 3R- and 4R-tau proteins in axonal growth cones were respectively diminished by treatment of taxol and nocodazole at low concentration. These results suggest that 3R-tau interacts with stable microtubules, while 4R-tau interacts with dynamic microtubules. Our finding implies that 3R- and 4R-tau may play differential roles in growth cones.
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