高等植物中SWI/SNF染色质重塑研究的新进展

染色质重塑是真核生物表观遗传调控的重要方式．通过对染色质物理结构的调节,染色质重塑在高等动植物干细胞的自我更新及分化、器官和个体发育以及肿瘤发生等多种生物学过程中发挥重要作用．近年来,高等动植物染色质重塑方面的研究已经成为表观遗传学研究领域的热点．本综述总结近年来有关高等动植物染色质重塑的重要研究报道,介绍了染色质重塑的结构机制、分析比较了高等动植物染色质重塑复合体的组成及其生物学功能的多样性,并着重综述了高等植物SWI/SNF染色质重塑复合体各组分在调控植物发育与逆境生长等方面的功能,以期为今后植物中染色质重塑的研究提供启示．     

Role of the SWI/SNF Chromatin Remodeling Complex in Regulation of Inflammation Gene Expression

Molecular Biology - The process of inflammation is the body’s natural defense response to the penetration of foreign substances and molecules from the outside. Many proteins, signaling...     

SWI3 subunits of putative SWI/SNF chromatin-remodeling complexes play distinct roles during Arabidopsis development

SWITCH/SUCROSE NONFERMENTING (SWI/SNF) chromatin-remodeling complexes mediate ATP-dependent alterations of DNA-histone contacts. The minimal functional core of conserved SWI/SNF complexes consists of a SWI2/SNF2 ATPase, SNF5, SWP73, and a pair of SWI3 subunits. Because of early duplication of the SWI3 gene family in plants, Arabidopsis thaliana encodes four SWI3-like proteins that show remarkable functional diversification. Whereas ATSWI3A and ATSWI3B form homodimers and heterodimers and interact with BSH/SNF5, ATSWI3C, and the flowering regulator FCA, ATSWI3D can only bind ATSWI3B in yeast two-hybrid assays. Mutations of ATSWI3A and ATSWI3B arrest embryo development at the globular stage. By a possible imprinting effect, the atswi3b mutations result in death for approximately half of both macrospores and microspores. Mutations in ATSWI3C cause semidwarf stature, inhibition of root elongation, leaf curling, aberrant stamen development, and reduced fertility. Plants carrying atswi3d mutations display severe dwarfism, alterations in the number and development of flower organs, and complete male and female sterility. These data indicate that, by possible contribution to the combinatorial assembly of different SWI/SNF complexes, the ATSWI3 proteins perform nonredundant regulatory functions that affect embryogenesis and both the vegetative and reproductive phases of plant development.     

Arabidopsis ARGONAUTE 1 Binds Chromatin to Promote Gene Transcription in Response to Hormones and Stresses

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Histone H1 Subtypes Differentially Modulate Chromatin Condensation without Preventing ATP-Dependent Remodeling by SWI/SNF or NURF

Although ubiquitously present in chromatin, the function of the linker histone subtypes is partly unknown and contradictory studies on their properties have been published. To explore whether the various H1 subtypes have a differential role in the organization and dynamics of chromatin we have incorporated all of the somatic human H1 subtypes into minichromosomes and compared their influence on nucleosome spacing, chromatin compaction and ATP-dependent remodeling. H1 subtypes exhibit different affinities for chromatin and different abilities to promote chromatin condensation, as studied with the Atomic Force Microscope. According to this criterion, H1 subtypes can be classified as weak condensers (H1.1 and H1.2), intermediate condensers (H1.3) and strong condensers (H1.0, H1.4, H1.5 and H1x). The variable C-terminal domain is required for nucleosome spacing by H1.4 and is likely responsible for the chromatin condensation properties of the various subtypes, as shown using chimeras between H1.4 and H1.2. In contrast to previous reports with isolated nucleosomes or linear nucleosomal arrays, linker histones at a ratio of one per nucleosome do not preclude remodeling of minichromosomes by yeast SWI/SNF or Drosophila NURF. We hypothesize that the linker histone subtypes are differential organizers of chromatin, rather than general repressors.     

The Arabidopsis SWI2/SNF2 Chromatin Remodeler BRAHMA Regulates Polycomb Function during Vegetative Development and Directly Activates the Flowering Repressor Gene SVP

The chromatin remodeler BRAHMA (BRM) is a Trithorax Group (TrxG) protein that antagonizes the functions of Polycomb Group (PcG) proteins in fly and mammals. Recent studies also implicate such a role for Arabidopsis (Arabidopsis thaliana) BRM but the molecular mechanisms underlying the antagonism are unclear. To understand the interplay between BRM and PcG during plant development, we performed a genome-wide analysis of trimethylated histone H3 lysine 27 (H3K27me3) in brm mutant seedlings by chromatin immunoprecipitation followed by next generation sequencing (ChIP-seq). Increased H3K27me3 deposition at several hundred genes was observed in brm mutants and this increase was partially supressed by removal of the H3K27 methyltransferase CURLY LEAF (CLF) or SWINGER (SWN). ChIP experiments demonstrated that BRM directly binds to a subset of the genes and prevents the inappropriate association and/or activity of PcG proteins at these loci. Together, these results indicate a crucial role of BRM in restricting the inappropriate activity of PcG during plant development. The key flowering repressor gene SHORT VEGETATIVE PHASE (SVP) is such a BRM target. In brm mutants, elevated PcG occupancy at SVP accompanies a dramatic increase in H3K27me3 levels at this locus and a concomitant reduction of SVP expression. Further, our gain- and loss-of-function genetic evidence establishes that BRM controls flowering time by directly activating SVP expression. This work reveals a genome-wide functional interplay between BRM and PcG and provides new insights into the impacts of these proteins in plant growth and development.