Institute of Cell Biology, University Witten/Herdecke, Witten, Germany.
Epigenetics Chromatin. 2008 Oct 27;1(1):3. doi: 10.1186/1756-8935-1-3.
In this study we exploit the unique genome organization of ciliates to characterize the biological function of histone modification patterns and chromatin plasticity for the processing of specific DNA sequences during a nuclear differentiation process. Ciliates are single-cell eukaryotes containing two morphologically and functionally specialized types of nuclei, the somatic macronucleus and the germline micronucleus. In the course of sexual reproduction a new macronucleus develops from a micronuclear derivative. During this process specific DNA sequences are eliminated from the genome, while sequences that will be transcribed in the mature macronucleus are retained.
We show by immunofluorescence microscopy, Western analyses and chromatin immunoprecipitation (ChIP) experiments that each nuclear type establishes its specific histone modification signature. Our analyses reveal that the early macronuclear anlage adopts a permissive chromatin state immediately after the fusion of two heterochromatic germline micronuclei. As macronuclear development progresses, repressive histone modifications that specify sequences to be eliminated are introduced de novo. ChIP analyses demonstrate that permissive histone modifications are associated with sequences that will be retained in the new macronucleus. Furthermore, our data support the hypothesis that a PIWI-family protein is involved in a transnuclear cross-talk and in the RNAi-dependent control of developmental chromatin reorganization.
Based on these data we present a comprehensive analysis of the spatial and temporal pattern of histone modifications during this nuclear differentiation process. Results obtained in this study may also be relevant for our understanding of chromatin plasticity during metazoan embryogenesis.
在这项研究中，我们利用纤毛虫独特的基因组组织来描述组蛋白修饰模式和染色质可塑性的生物学功能，这些模式和可塑性在核分化过程中用于处理特定的 DNA 序列。纤毛虫是含有两种形态和功能上专门化的核的单细胞真核生物，即体细胞大核和生殖系小核。在有性生殖过程中，一个新的大核从小核衍生物中发育而来。在此过程中，基因组中会删除特定的 DNA 序列，而在成熟大核中转录的序列则会保留下来。
我们通过免疫荧光显微镜、Western 分析和染色质免疫沉淀（ChIP）实验表明，每种核类型都建立了其特定的组蛋白修饰特征。我们的分析表明，早期大核原基在两个异染色质生殖系小核融合后立即采用了一种许可的染色质状态。随着大核发育的进行，新引入的抑制性组蛋白修饰指定了要删除的序列。ChIP 分析表明，许可性组蛋白修饰与将在新大核中保留的序列相关。此外，我们的数据支持以下假设：一种 PIWI 家族蛋白参与核间的交叉对话，并在 RNAi 依赖性的发育性染色质重排控制中发挥作用。
基于这些数据，我们对核分化过程中组蛋白修饰的时空模式进行了全面分析。本研究获得的结果也可能与我们对后生动物胚胎发生过程中染色质可塑性的理解有关。
