Reproductive Capability of Maternal Centrosomes in the Tubifex Egg

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Tubifex eggs individually inherit a single maternal centrosome during the first mitosis (mitosis I), and thereby form an asymmetrically organized monastral mitotic apparatus for the unequal cleavage. This maternal centrosome does not duplicate itself at the transition to mitosis I but does so at the transition to the second mitosis (Shimizu T, 1996, Roux's Arch Dev Biol 205 : 290-299). To examine whether the maternal centrosome duplication is under cytoplasmic control, we produced syncytial eggs by electric fusion of an early meiosis II egg with an early mitosis I egg in an equator-to-equator fashion. As suggested from the diffusion rate of microinjected Texas Red-dextran (10, 000 MW), diffusible ooplasmic components in syncytial eggs appear to be intermingled within 20 min following fusion. At〜120 min after fusion, the meiosis II spindle and the mitosis I nucleus in each syncytial egg complete respective meiosis and mitosis almost simultaneously. Shortly after competion of the meiosis/mitosis, syncytial eggs individually exhibit three centrosomes, two of which are associated with a nucleus derived from the mitosis I spindle, and the remaining one with a nucleus derived from the meiosis II spindle. These results suggest that maternal (meiosis II) centrosomes fail to duplicate under cytoplawsmic conditions that favor the duplication of mitotic centrosomes and taht meiosis II centrosomes are intrinsically distinct from mitotic centrosomes. We propose that inhibitory factors that block centrosome duplication are associated with meiotic centrosomes and that their release during mitosis I gives rise to reproduction-competent maternal centrosomes.
社団法人日本動物学会の論文

Reproductive Capability of Maternal Centrosomes in the Tubifex Egg

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