Electron microscopic 3D-analysis of veasts and various mutants during the ascospore formation

在酵母的子囊孢子形成过程中有多种形态变化过程。众所周知，许多基因与产孢有关。为了了解这些基因的功能，我们利用电子显微镜对酵母的精细结构进行了详细的研究，并重建了酵母的三维超微结构。采用冷冻取代法固定出芽酵母（Saccharomyces cerevisiae）和裂变酵母（Schizosaccharomyces pombe），树脂包埋后连续切片。通过摄影和计算机进行三维重建。用不同的芽殖酵母突变体观察发现，核融合是从外核膜开始的。在裂变酵母中，在核融合和马尾期细胞质中有许多微管，而细胞核中没有微管。它们位于细胞核周围的细胞尖端。而在SPB核融合过程中，芽殖酵母的细胞质和细胞核中可见微管。两种酵母减数分裂II的spb都进行了修饰。裂变酵母的spb分化为几层斑块，而出芽酵母的spb则变成清晰而大的外层斑块。减数分裂I后，分裂酵母的细胞核分裂为2个核，出芽酵母与减数分裂I前一样只有1个核。减数分裂II后，两个酵母都分裂为4个核，成为4个子囊孢子。

There are various processes of morphological changes during the ascospore formation of yeasts. It is known that many genes are related to the sporulation. To understand the function of these genes, we studied the fine structure of yeasts in detail by electron microscopy , and reconstructed the 3-dimensional ultrastructure of the yeasts.Budding yeast (Saccharomyces cerevisiae) and fission yeast (Schizosaccharomyces pombe) were fixed by the freeze substitution method, then serial sections after resin embedding were made. Three-dimensional reconstruction was carried out by photographing and the use of a computer.It was shown that the nuclear fusion was initiated from the outer nuclear membrane when it was observed using various mutants of budding yeast. In fission yeast, it was shown that many microtubules were in the cytoplasm during nuclear fusion and the horse tail stage, but no microtubule was in the nucleus. They localized in the tip of the cell from the circumference of the nucleus.In contrast, microtubules of the budding yeast were observed in the cytoplasm and the nucleus from SPB during nuclear fusion.The SPBs of meiosis II were modified in both yeasts. The SPBs of the fission yeast were differentiated into several layers of plaques, but the SPBs of the budding yeast were changed into clear and large outer plaques. After meiosis I, the nucleus was divided into 2 nuclei of fission yeast, but the budding yeast had 1 nucleus as before meiosis I.After meiosis II, both yeasts were divided into 4 nuclei, and became 4 ascospores.