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

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.