Nuclear behavior during conjugation and meiosis in the fission yeast Schizosaccharomyces pombe.

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Abstract
The fine structure involved with the nuclear behavior occurring during conjugation and meiosis in the fission yeast S. pombe was studied by serial thin sectioning and EM. A pair of haploid cells conjugated via a cytoplasmic isthmus where cytoplasmic vesicles accumulated. The fusion of the 2 nuclei was preceded by the fusion of respective nucleus-associated organelles (NAO), and the prophase I nucleus, taking an elongated shape with the fused NAO at 1 end, contained strands of dense linear elements whose number and distribution were not constant, as seen in the 3-dimensional reconstruction of serial sections. The 1st meiotic division was carried out by the spindle, being a preserved nuclear envelope, in which chromosomal microtubules were associated with opposite NAO connected by the pole-to-pole microtubules. The 2nd meiotic division proceeded, almost synchronously in the 2 separate nuclei, the formation of the forespore membrane beginning at the cytoplasmic side of the differentiated NAO.