Iwamoto Masaaki, Koujin Takako, Osakada Hiroko, Mori Chie, Kojidani Tomoko, Matsuda Atsushi, Asakawa Haruhiko, Hiraoka Yasushi, Haraguchi Tokuko
Advanced ICT Research Institute Kobe, National Institute of Information and Communications Technology (NICT), Kobe 651-2492, Japan.
Advanced ICT Research Institute Kobe, National Institute of Information and Communications Technology (NICT), Kobe 651-2492, Japan Japan Women's University, Tokyo 112-8681, Japan.
J Cell Sci. 2015 May 1;128(9):1812-23. doi: 10.1242/jcs.167353. Epub 2015 Mar 18.
Ciliates have two functionally distinct nuclei, a somatic macronucleus (MAC) and a germline micronucleus (MIC) that develop from daughter nuclei of the last postzygotic division (PZD) during the sexual process of conjugation. Understanding this nuclear dimorphism is a central issue in ciliate biology. We show, by live-cell imaging of Tetrahymena, that biased assembly of the nuclear pore complex (NPC) occurs immediately after the last PZD, which generates anterior-posterior polarized nuclei: MAC-specific NPCs assemble in anterior presumptive MACs but not in posterior presumptive MICs. MAC-specific NPC assembly in the anterior nuclei occurs much earlier than transport of Twi1p, which is required for MAC genome rearrangement. Correlative light-electron microscopy shows that addition of new nuclear envelope (NE) precursors occurs through the formation of domains of redundant NE, where the outer double membrane contains the newly assembled NPCs. Nocodazole inhibition of the second PZD results in assembly of MAC-specific NPCs in the division-failed zygotic nuclei, leading to failure of MIC differentiation. Our findings demonstrate that NPC type switching has a crucial role in the establishment of nuclear differentiation in ciliates.
纤毛虫有两个功能不同的细胞核，一个是体细胞大核（MAC），另一个是生殖系小核（MIC），它们在接合的有性过程中从最后一次合子后分裂（PZD）的子核发育而来。理解这种核二态性是纤毛虫生物学的核心问题。我们通过对嗜热四膜虫的活细胞成像显示，在最后一次PZD后立即发生核孔复合体（NPC）的偏向组装，这产生了前后极化的细胞核：MAC特异性NPC在前体MAC中组装，但不在后体MIC中组装。前体细胞核中MAC特异性NPC的组装比MAC基因组重排所需的Twi1p的转运要早得多。相关光电子显微镜显示，新的核膜（NE）前体的添加是通过冗余NE结构域的形成发生的，其中外双膜包含新组装的NPC。诺考达唑对第二次PZD的抑制导致在分裂失败的合子核中组装MAC特异性NPC，导致MIC分化失败。我们的研究结果表明，NPC类型转换在纤毛虫核分化的建立中起关键作用。
