| Summary: | 博士 === 國防醫學院 === 生命科學研究所 === 100 === Autophagy is an evolutionarily conserved mechanism for the degradation of cellular components, but its role in enucleation during differentiation has not been established. Tetrahymena thermophila is a unicellular eukaryote with two functionally distinct nuclei, the somatic (macro-) and the germline (micro-) nucleus. These nuclei are produced during sexual reproduction (conjugation), which involves differentiation and selective degradation of several specific nuclei. To examine the role of autophagy in nuclear degradation, we studied the function of one ATG6, one ATG5, and two ATG8 genes in Tetrahymena. Through fluorescent protein-tagging, we found that two ATG8 proteins are targeted to degrading nuclei at specific stages, with some enrichment on the nuclear periphery, suggesting the formation of autophagosomes surrounding these nuclei. In addition, the ATG8 knockout mutant cells showed a pronounced delay in nuclear degradation without apparently preventing the completion of other developmental events. The results showed differential roles for two ATG8 genes, with ATG8-65 playing a more significant role in starvation than ATG8-2, though both are important in nuclear degradation. Analysis of ATG5 also showed a specific function in starvation and affected the nuclear degradation as ATG8-65. Besides, knockout of ATG6 explored a surprising putative vegetative essential role for this gene in Tetrahymena. These evidences provided direct support for a critical role for autophagy not only in programmed nuclear degradation, but could be also in vegetative growth.
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