Maruta H, Goldstein L
J Cell Biol. 1975 Jun;65(3):631-45. doi: 10.1083/jcb.65.3.631.
The synthesis and behavior of Amoeba proteus nuclear envelope (NE) phospholipids were studied. Most NE phospholipid synthesis occurs during G2 and little during mitosis or S. (A. proteus has no G1 phase). Autoradiographic observations after implantation of [3-H] choline nuclei into unlabeled cells reveal little turnover of NE phospholipid during interphase but during mitosis all the label is dispersed through the cytoplasm. Beginning at telophase all the label is dispersed through the cytoplasm. Beginning at telophase all the NE phospholipid label returns to the daughter NEs. This observation, along with the finding that no NE phospholipid synthesis occurs during mitosis or S, indicates that no de novo NE phospholipid production is required for newly forming NEs. Similarlyemetine, at concentrations that inhibit 97 percent of protein synthesis, does not prevent the post mitotic formation of NEs, suggesting that previously manufactured proteins are used in making new NEs. If a nucleus containing labeled NE phospholipids is transplanted into an unlabeled nucleate cell and the cell is allowed to grow and divide, the resultant four nuclei are equally labeled. This finding supports, but does not prove (see next paragraph), the conclusion that there probably is no continuity of the A. proteus NE during mitosis. When a phospholipid-labeled nucleus is implanted into a cell in mitosis, the grafted nucleus is not induced to enter mitosis. There is, however, a marked increase in the turnover of that nucleus's NE phospholipids with no apparent breakdown of the NE; this indicated that the mitotic cytoplasm possesses a factor that stimulates NE phospholipid exchange with the cytoplasm. That enhanced turnover is not accompanied by visible structural alteration makes less certain the earlier conclusion that no NE continuity exists during mitosis. Perhaps the most important finding in this study is that there are present, at restricted times in the cell cycle, factors capable of inducing accelerated exchange of structural components without microscopically detectable disruptions of structure.
对变形虫细胞核膜（NE）磷脂的合成及行为进行了研究。大多数NE磷脂合成发生在G2期，而在有丝分裂期或S期很少发生（变形虫没有G1期）。将[3-H]胆碱核植入未标记细胞后进行放射自显影观察发现，间期NE磷脂的周转很少，但在有丝分裂期所有标记物都分散到细胞质中。从末期开始，所有标记物都分散到细胞质中。从末期开始，所有NE磷脂标记物都回到子细胞核膜。这一观察结果，连同在有丝分裂期或S期不发生NE磷脂合成这一发现，表明新形成的核膜不需要从头合成NE磷脂。同样，在抑制97%蛋白质合成的浓度下，emetine并不阻止有丝分裂后核膜的形成，这表明先前制造的蛋白质被用于制造新的核膜。如果将含有标记NE磷脂的细胞核移植到未标记的有核细胞中，并让该细胞生长和分裂，那么产生的四个细胞核会被等量标记。这一发现支持但未证明（见下一段）这样的结论：在有丝分裂期间变形虫的核膜可能不存在连续性。当将一个磷脂标记的细胞核植入处于有丝分裂期的细胞中时，移植的细胞核不会被诱导进入有丝分裂。然而，该细胞核的NE磷脂周转显著增加，而核膜没有明显破裂；这表明有丝分裂细胞质中存在一种因子，可刺激NE磷脂与细胞质进行交换。这种增强的周转并没有伴随着可见的结构改变，这使得早期关于有丝分裂期间不存在核膜连续性的结论变得不那么确定。也许这项研究中最重要的发现是，在细胞周期的特定时间存在一些因子，这些因子能够在显微镜下检测不到结构破坏的情况下诱导结构成分的加速交换。
