Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033, Japan.
Curr Biol. 2010 Nov 9;20(21):1913-8. doi: 10.1016/j.cub.2010.09.004. Epub 2010 Oct 21.
In eukaryotic cells, the nuclear envelope partitions the nucleus from the cytoplasm. The fission yeast Schizosaccharomyces pombe undergoes closed mitosis in which the nuclear envelope persists rather than being broken down, as in higher eukaryotic cells. It is therefore assumed that nucleocytoplasmic transport continues during the cell cycle. Here we show that nuclear transport is, in fact, abolished specifically during anaphase of the second meiotic nuclear division. During that time, both nucleoplasmic and cytoplasmic proteins disperse throughout the cell, reminiscent of the open mitosis of higher eukaryotes, but the architecture of the S. pombe nuclear envelope itself persists. This functional alteration of the nucleocytoplasmic barrier is likely induced by spore wall formation, because ectopic induction of sporulation signaling leads to premature dispersion of nucleoplasmic proteins. A photobleaching assay demonstrated that nuclear envelope permeability increases abruptly at the onset of anaphase of the second meiotic division. The permeability was not altered when sporulation was inhibited by blocking the trafficking of forespore-membrane vesicles from the endoplasmic reticulum to the Golgi. The evidence indicates that yeast gametogenesis produces vesicle transport-mediated forespore membranes by inducing nuclear envelope permeabilization.
在真核细胞中，核膜将细胞核与细胞质分隔开来。裂殖酵母 Schizosaccharomyces pombe 经历封闭的有丝分裂，核膜在细胞分裂过程中保持完整，而不会像高等真核细胞那样被分解。因此，人们认为核质转运在细胞周期中持续进行。在这里，我们表明，核转运实际上在第二次减数分裂的后期被特异性地阻断。在这段时间里，核质蛋白和细胞质蛋白都分散到整个细胞中，这让人联想到高等真核生物的开放有丝分裂，但裂殖酵母核膜本身的结构仍然存在。这种核质屏障的功能改变很可能是由孢子壁形成引起的，因为诱导孢子形成信号的异位表达会导致核质蛋白过早分散。荧光漂白实验表明，第二次减数分裂后期核膜的通透性突然增加。当通过阻断从内质网到高尔基体的前孢子膜小泡的运输来抑制孢子形成时，通透性没有改变。这些证据表明，酵母配子发生通过诱导核膜通透性来产生囊泡运输介导的前孢子膜。
