Liu Ming-Liang, Yao Meng-Chao
Graduate Institute of Life Sciences, National Defense Medical Center, Min-Chuan, Taipei, Taiwan, Republic of China.
Eukaryot Cell. 2012 Apr;11(4):494-506. doi: 10.1128/EC.05296-11. Epub 2012 Feb 24.
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 germ line (micro-) nuclei. 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 two ATG8 genes in Tetrahymena. Through fluorescent protein tagging, we found that both 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, ATG8 knockout mutant cells showed a pronounced delay in nuclear degradation without apparently preventing the completion of other developmental events. This evidence provided direct support for a critical role for autophagy in programmed nuclear degradation. The results also showed differential roles for two ATG8 genes, with ATG8-65 playing a more significant role in starvation than ATG8-2, although both are important in nuclear degradation.
自噬是一种在进化上保守的细胞成分降解机制，但其在分化过程中的去核作用尚未明确。嗜热四膜虫是一种单细胞真核生物，具有两个功能不同的细胞核，即体细胞（大）核和生殖系（小）核。这些细胞核在有性生殖（接合）过程中产生，该过程涉及几个特定细胞核的分化和选择性降解。为了研究自噬在细胞核降解中的作用，我们研究了嗜热四膜虫中两个ATG8基因的功能。通过荧光蛋白标记，我们发现这两种蛋白在特定阶段都靶向降解中的细胞核，在核周边有一些富集，表明围绕这些细胞核形成了自噬体。此外，ATG8基因敲除突变细胞在细胞核降解方面表现出明显延迟，但显然并未阻止其他发育事件的完成。这一证据为自噬在程序性细胞核降解中的关键作用提供了直接支持。结果还显示了两个ATG8基因的不同作用，尽管两者在细胞核降解中都很重要，但ATG8 - 65在饥饿状态下比ATG8 - 2发挥更重要的作用。
