Analysis on the nuclear apoptosis indispensable for sexual reproduction in a ciliate, Paramecium.

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Programmed nuclear death occurs in unicellular eukaryotes such as ciliates. In the present work, nuclear apoptosis was investigated from the point of view of nuclear interaction among maternal macronuclei, newly developed macronuclei, maternal micronuclei and newly developed micronuclei. In Paramecium caudatum, programmed nuclear death occurs three times during conjugation (Mikami, 2000).The first of the three selective nuclear degeneration events occurring is the degeneration of meiotic products of the micronucleus. When cells enter the conjugative phase the micronucleus undergoes meiosis and produces four haploid micronuclei. One of these moves into an area called the paroral cone and survives while the other three soon degenerate.The remaining nucleus divides once and produces gametic nuclei (gametogenesis). The gametic micronuclei are exchanged reciprocally between mating cells and form diploid zygotic nuclei. A zygotic nucleus (synkaryon) divides three times to give rise to eight … More nuclei. Four of these differentiate into macronuclear anlagen and the other four became presumptive micronuclei. The four macronuclear anlagen are distributed without nuclear division to daughter cells in two cell divisions after conjugation. For the four presumptive micronuclei, it is known that one remains and the other three degenerate. This is the second nuclear degeneration. The results obtained lead us to a conclusion that most of the micronuclei remained at least by the first post-conjugation fission and that only one of them was selected to divide at the first fission (Taka et al, 2005).The third selective degeneration of nuclei occurs with the parental macronucleus and the macronuclear anlagen (Kimura et al., 2004). After conjugation, the parental macronucleus fragments into pieces that retain the functions of the macronucleus. After several fissions, however, the macronuclear fragments degenerate selectively. If newly developed macronucleus was removed just before the degeneration of macronuclear fragments, the gene expression of the fragments could be reprogrammed to be juvenile (Kimura and Mikami, 2003). Less