Biozentrum, Ludwig-Maximilians University Munich, Grosshadernerstrasse 2, 82152 Planegg-Martinsried, Germany; Department of Medical Biology, Medical University-Plovdiv, Boulevard Vasil Aprilov 15A, Plovdiv 4000, Bulgaria.
Institute for Medical Engineering and Science, and Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Department of Physics, University of Chicago, 929 E 57th St, Chicago, IL 60637, USA.
Trends Cell Biol. 2020 Apr;30(4):276-289. doi: 10.1016/j.tcb.2019.12.008. Epub 2020 Jan 22.
The cell nucleus is a remarkably well-organized organelle with membraneless but distinct compartments of various functions. The largest of them, euchromatin and heterochromatin, are spatially segregated in such a way that the transcriptionally active genome occupies the nuclear interior, whereas silent genomic loci are preferentially associated with the nuclear envelope. This rule is broken by rod photoreceptor cells of nocturnal mammals, in which the two major compartments have inverted positions. The inversion and dense compaction of heterochromatin converts these nuclei into microlenses that focus light and facilitate nocturnal vision. As is often the case in biology, when a mutation helps to understand normal processes and structures, inverted nuclei have served as a tool to unravel general principles of nuclear organization, including mechanisms of heterochromatin tethering to the nuclear envelope, autonomous behavior of small genomic segments, and euchromatin-heterochromatin segregation.
细胞核是一个组织高度有序的细胞器，尽管没有膜结构，但具有各种不同功能的无膜区室。其中最大的两个区室，常染色质和异染色质，以空间分隔的方式排列，转录活跃的基因组占据核内部，而沉默的基因组位点则优先与核膜相关联。这一规则被夜间活动的哺乳动物的棒状光感受器细胞所打破，在这些细胞中，两个主要的区室位置颠倒。异染色质的反转和密集压缩将这些细胞核转化为微透镜，聚焦光线并促进夜间视觉。在生物学中，当一个突变有助于理解正常过程和结构时，这种情况经常发生，反转的细胞核已成为揭示核组织一般原则的工具，包括异染色质与核膜连接的机制、小基因组片段的自主行为以及常染色质和异染色质的分离。
