The somatic macronucleus (MAC) and germline micronucleus (MIC) of Tetrahymena thermophila differ in chromosome numbers, sizes, functions, transcriptional activities, and cohesin complex location. However, the higher-order chromatin organization in T. thermophila is still largely unknown. Here, we explored the higher-order chromatin organization in the two distinct nuclei of T. thermophila using the Hi-C and HiChIP methods. We found that the meiotic crescent MIC has specific chromosome interaction pattern, with all the telomeres or centromeres on the five MIC chromosomes clustering together, respectively, which is also helpful to identify the midpoints of centromeres in the MIC. We revealed that the MAC chromosomes lack A/B compartments, topologically associating domains (TADs) and chromatin loops. The MIC chromosomes have TAD-like structures, but not A/B compartments and chromatin loops. The boundaries of the TAD-like structures in the MIC are highly consistent with the chromatin breakage sequence (CBS) sites, suggesting that each TAD-like structure of the MIC chromosomes develops into one MAC chromosome during MAC development, which provides a mechanism of the formation of MAC chromosomes during conjugation. Overall, we demonstrated the distinct higher-order chromatin organization in the two nuclei of the T. thermophila and suggest that the higher-order chromatin structures may play important roles during the development of the MAC chromosomes.

中文翻译：

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大核染色体的重排对应于嗜热四膜膜虫中微核染色体的TAD样结构。

嗜热四膜膜虫的体细胞大核（MAC）和种系微核（MIC）在染色体数目，大小，功能，转录活性和粘着蛋白复合体位置方面有所不同。然而，在嗜热菌中较高等级的染色质组织仍然是未知的。在这里，我们使用Hi-C和HiChIP方法探索了嗜热假丝酵母两个不同核中的高级染色质组织。我们发现减数分裂新月MIC具有特定的染色体相互作用模式，五个MIC染色体上的所有端粒或着丝粒分别聚集在一起，这也有助于确定MIC着丝粒的中点。我们发现，MAC染色体缺少A / B区室，拓扑关联域（TAD）和染色质环。MIC染色体具有TAD样结构，但没有A / B隔室和染色质环。MIC中TAD样结构的边界与染色质断裂序列（CBS）位点高度一致，这表明MIC染色体的每个TAD样结构在MAC发育过程中都发育成一个MAC染色体，这提供了一种机制。接合过程中MAC染色体的形成。总的来说，我们证明了嗜热毁丝球菌两个核中独特的高阶染色质组织，并暗示了高阶染色质结构可能在MAC染色体的发育过程中发挥重要作用。提示MIC染色体的每个TAD样结构在MAC发育过程中均发育为一个MAC染色体，这为结合过程中MAC染色体的形成提供了一种机制。总的来说，我们证明了嗜热毁丝球菌两个核中独特的高阶染色质组织，并暗示了高阶染色质结构可能在MAC染色体的发育过程中发挥重要作用。提示MIC染色体的每个TAD样结构在MAC发育过程中均发育为一个MAC染色体，这为结合过程中MAC染色体的形成提供了一种机制。总的来说，我们证明了嗜热毁丝球菌两个核中独特的高阶染色质组织，并暗示了高阶染色质结构可能在MAC染色体的发育过程中发挥重要作用。