Ultrastructure analysis of germinal nucleus and its differentiation to the vegetative nucleus in Paramecium bursaria.

草履虫的微核由密集的染色体染色质、微板和微管、中间丝等细胞骨架组成。染色体由50 nm的染色质丝组成，这些染色质丝相互缠绕在一起，形成200 nm的染色体，即使在间期也是如此。至少有一部分染色体被微板覆盖。在细胞分裂过程中，200 nm的染色体一起被移到极点。另一方面，在接合细胞中，观察到直径300 nm、长度可达5微米的典型的端粒染色体。这些300 nm的染色体比分裂细胞时观察到的200 nm的染色体密度要低。微核染色质在对数生长期已经疏松，但50 nm纤维仍是电子致密的，说明微核染色质基本凝聚为50 nm异染色丝。与微核不同，大核染色质即使在细胞分裂时也不会组织成染色体，而是形成直径150 nm的染色质小体。染色质小体的长度随生长期的变化而变化。在对数阶段，它们是短的，但在稳定期，它们是长的和分枝的。大核和微核是从结合细胞的合核中区分出来的。可辨认的大核原核示微板变性，染色体染色质解聚。在发育过程中，Anlage充满了20 nm的细丝，然后它们聚集在一起构成初级染色质小体。用染色质铺展的方法分析了大核DNA包装成染色质小体的方式。染色质铺展显示，11 nm的核小体卷曲形成20-30 nm的细丝。这些细丝进一步卷曲形成50-60 nm的细丝，这些细丝折叠起来形成150 nm的染色质小体。由于质量分离困难，目前还不能分析微核染色质。

In Paramecium bursaria, micronuclei are composed of dense chromosomal chromatin, microlamella and cytoskeletal components, such as microtubules and intermediate filaments. Chromosome consists of 50 nm chromatin filaments, which are intertwisted to make 200 nm chromosomes even at interphase. At least a part of the chromosomes are covered by the microlamella. During cell division, 200 nm chromosomes are moved to the pole together with each other. On the other hand, in the conjugating cells, typical telocentric chromosomes of 300 nm in diameter and up to 5 mum in length are observed. These 300 nm chromosomes are less dense than the 200 nm one observed in dividing cells. Micronuclear chromatin are loosened at the log-phase of growth, but the 50 nm fiber are still electron dense, suggesting the micronuclear chromatin are basically condensed as the 50 nm heterochromatic filaments. In contrast to the micronucleus, the macronuclear chromatin are not organized into chromosomes even at cell division, but construct chromatin bodies of 150 nm in diameter. Length of the chromatin body changes during growth stage. In the log-phase, they are short, but in the stationary phase, they long and branched. Macro-and micronuclei are differentiated from the synkaryon of the conjugating cells. Recognizable macronuclear anlage shows degenerated microlamellae and decondensed chromosomal chromatin. During development, anlage is filled with 20 nm filaments, then they aggregate to construct primary chromatin bodies. The manner of packing the macronuclear DNA into chromatin bodies are analyzed by the chromatin spreading method using isolated macronuclei. Spread chromatin showed that the 11 nm nucleosomes are coiled to form 20-30 nm filaments. These filaments further coiled to form 50-60 nm filaments, which are folded to build up the 150 nm chromatin bodies. Because of difficulty of mass-isolation, micronuclear chromatin can not yet be analyzed.