| Research Abstract |
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.
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