Fransz Paul, De Jong J Hans, Lysak Martin, Castiglione Monica Ruffini, Schubert Ingo
Institute of Plant Genetics and Crop Plant Research (IPK), D-06466 Gatersleben, Germany.
Proc Natl Acad Sci U S A. 2002 Oct 29;99(22):14584-9. doi: 10.1073/pnas.212325299. Epub 2002 Oct 16.
Heterochromatin in the model plant Arabidopsis thaliana is confined to small pericentromeric regions of all five chromosomes and to the nucleolus organizing regions. This clear differentiation makes it possible to study spatial arrangement and functional properties of individual chromatin domains in interphase nuclei. Here, we present the organization of Arabidopsis chromosomes in young parenchyma cells. Heterochromatin segments are organized as condensed chromocenters (CCs), which contain heavily methylated, mostly repetitive DNA sequences. In contrast, euchromatin contains less methylated DNA and emanates from CCs as loops spanning 0.2-2 Mbp. These loops are rich in acetylated histones, whereas CCs contain less acetylated histones. We identified individual CCs and loops by fluorescence in situ hybridization by using rDNA clones and 131 bacterial artificial chromosome DNA clones from chromosome 4. CC and loops together form a chromosome territory. Homologous CCs and territories were associated frequently. Moreover, a considerable number of nuclei displayed perfect alignment of homologous subregions, suggesting physical transinteractions between the homologs. The arrangement of interphase chromosomes in Arabidopsis provides a well defined system to investigate chromatin organization and its role in epigenetic processes.
模式植物拟南芥中的异染色质局限于所有五条染色体的小的着丝粒周围区域以及核仁组织区。这种清晰的分化使得研究间期细胞核中单个染色质结构域的空间排列和功能特性成为可能。在这里，我们展示了拟南芥染色体在幼嫩薄壁细胞中的组织情况。异染色质片段组织成浓缩的染色中心（CCs），其包含高度甲基化的、大多为重复的DNA序列。相比之下，常染色质含有较少甲基化的DNA，并以跨越0.2 - 2兆碱基对的环的形式从染色中心发出。这些环富含乙酰化组蛋白，而染色中心含有较少的乙酰化组蛋白。我们通过使用rDNA克隆和来自4号染色体的131个细菌人工染色体DNA克隆，通过荧光原位杂交鉴定了单个染色中心和环。染色中心和环共同形成一个染色体区域。同源染色中心和区域频繁关联。此外，相当数量的细胞核显示同源亚区域完美对齐，表明同源物之间存在物理性的跨相互作用。拟南芥中间期染色体的排列提供了一个明确的系统来研究染色质组织及其在表观遗传过程中的作用。
