Kimura Naomi, Mikami Kazuyuki
EEC, Miyagi University of Education, Sendai 980-0845, Japan.
Differentiation. 2003 Aug;71(6):337-45. doi: 10.1046/j.1432-0436.2003.7106004.x.
The macronucleus of Paramecium caudatum controls most cellular activities, including sexual immaturity after conjugation. Exconjugant cells have two macronuclear forms: (1) fragments of the maternal macronucleus, and (2) the new macronuclei that develop from the division products of a fertilization micronucleus. The fragments are distributed into daughter cells without nuclear division and persist for at least eight cell cycles after conjugation. Conjugation between heterokaryons revealed that the fragmented maternal macronuclei continued to express genetic information for up to eight cell cycles. When the newly developed macronucleus was removed artificially within four cell cycles after conjugation, the clones regenerated the macronuclear fragments (macronuclear regeneration; MR) and showed mating reactivity, because they were sexually mature. However, when the new macronucleus was removed during later stages, many MR clones did not show mating reactivity. In some extreme cases, immaturity continued for more than 50 fissions after conjugation, as seen with normal clones that had new macronuclei derived from a fertilization micronucleus. These results indicate that the immaturity determined by the new macronucleus is not annulled by the regenerated maternal macronucleus. Mature macronuclear fragments may be "reprogrammed" in the presence of the new macronucleus, resulting in their expression of "immaturity."
尾草履虫的大核控制着大多数细胞活动，包括接合后性不成熟。接合后细胞有两种大核形式：（1）母本大核的片段，以及（2）由受精小核的分裂产物发育而来的新大核。这些片段在不进行核分裂的情况下分布到子细胞中，并在接合后持续至少八个细胞周期。异核体之间的接合表明，碎片化的母本大核在多达八个细胞周期内持续表达遗传信息。当在接合后的四个细胞周期内人工去除新发育的大核时，克隆体会再生大核片段（大核再生；MR）并表现出交配反应性，因为它们已经性成熟。然而，当在后期去除新大核时，许多MR克隆体并未表现出交配反应性。在一些极端情况下，接合后不成熟状态会持续超过50次分裂，就像具有源自受精小核的新大核的正常克隆体一样。这些结果表明，由新大核决定的不成熟状态不会被再生的母本大核消除。成熟的大核片段可能在新大核存在的情况下被“重新编程”，从而导致它们表现出“不成熟”。
