Current models suggest that chromosome domains segregate into either an active (A) or inactive (B) compartment. B-compartment chromatin is physically separated from the A compartment and compacted by the nuclear lamina. To examine these models in the developmental context of C. elegans embryogenesis, we undertook chromosome tracing to map the trajectories of entire autosomes. Early embryonic chromosomes organized into an unconventional barbell-like configuration, with two densely folded B compartments separated by a central A compartment. Upon gastrulation, this conformation matured into conventional A/B compartments. We used unsupervised clustering to uncover subpopulations with differing folding properties and variable positioning of compartment boundaries. These conformations relied on tethering to the lamina to stretch the chromosome; detachment from the lamina compacted, and allowed intermingling between, A/B compartments. These findings reveal the diverse conformations of early embryonic chromosomes and uncover a previously unappreciated role for the lamina in systemic chromosome stretching.

中文翻译：

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早期秀丽隐杆线虫胚胎的层依赖拉伸和非常规染色体室。

当前的模型表明染色体结构域可分为活动（A）或不活动（B）隔室。B室染色质与A室物理分离，并被核层致密。为了在秀丽隐杆线虫胚胎发生的发育环境中检查这些模型，我们进行了染色体示踪以绘制整个常染色体的轨迹。早期胚胎染色体组织成非常规的杠铃状结构，两个密集折叠的B间隔被中央A间隔隔开。气化后，该构象成熟为常规的A / B隔室。我们使用无监督的聚类来发现具有不同折叠属性和可变区室边界位置的亚种群。这些构象依赖于与椎板的束缚来拉伸染色体。层板脱离，压实，并允许在A / B隔室之间混合。这些发现揭示了早期胚胎染色体的各种构象，并揭示了在系统染色体伸展中叶片先前未曾意识到的作用。