File Name: role of chromatin in gene expression and gene silencing .zip
- Regulation of gene expression
- Overview: Eukaryotic gene regulation
- RNA meets chromatin
- The role of WDR5 in silencing human fetal globin gene expression
Metrics details. Histone modifications play pivotal roles in chromatin remodeling and gene regulation. Rice genome possesses multiple genes encoding different classes of histone modification enzymes. Specific histone modification patterns in rice are associated with either heterochromatic or euchromatic regions or related to gene expression.
Regulation of gene expression
Metrics details. One of the cellular defenses against virus infection is the silencing of viral gene expression. There is evidence that at least two gene-silencing mechanisms are used against the human immuno-deficiency virus HIV. Paradoxically, this cellular defense mechanism contributes to viral latency and persistence, and we review here the relationship of viral latency to gene-silencing mechanisms. To succeed, all long-term relationships require some degree of compromise from both partners. This is no less true for persistent virus infections and their hosts.
Overview: Eukaryotic gene regulation
Epigenetics is the study of inherited changes in phenotype appearance or gene expression that are caused by mechanisms other than changes in the underlying DNA sequence 1 , 2. These changes may persist through multiple cell divisions, even for the remainder of the cell's life, and may also last for multiple generations. However, to reiterate, there is no change in the underlying DNA sequence of the organism. The most significant epigenetic mechanisms include DNA methylation, histone modifications, and the processes mediated by the most recently discovered class, the non-coding RNAs 3. DNA methylation is defined as the selective methylation addition of a methyl group of cytosine within a CpG dinucleotide, thereby forming 5-methylcytosine 4 , 5. The first type, DNMT1, mainly plays a role in the maintenance of methylation, can methylate the hemi-methylated cytosine in double-stranded DNA molecules, and may be involved in the methylation of the newly synthesized strand during replication of duplex DNA 6. DNA methylation is generally associated with gene silencing 7 , and DNA demethylation is usually connected with gene activation 8 —
For decades, chromatin was considered to be an inert structure whose only role was the compacting and confining of DNA inside the eukaryotic nucleus. However, tremendous progress in this field over the last 10 years has dramatically elevated chromatin to a key position in the control of gene activity. Its role in mediating the transformation of a normal cell into a malignant state is particularly interesting. On one side of this story there is the discovery that aberrant methylation patterns in an increasing number of tumour suppressor and DNA repair genes determine carcinogenetic transformation; while on the other side, there is the existence of a series of methyl-DNA binding activities that recruit co-repressor complexes and modify the structure of the chromatin to produce a transcriptionally silenced state. Although this field has seen rapid progress in recent years, detailed mechanisms by which this machinery modifies chromatin structure to its appropriate state and the specific targeting of repressor complexes have yet to be resolved.
RNA meets chromatin
These genes are expressed in a developmental stage- and tissue-specific manner, which is governed by a combination of transcriptional regulation and epigenetic tuning. A large body of evidence has shown that epigenetic marks generated by modification of the amino-terminal tails of histones play important roles in altering chromatin structure and function, thereby controlling the transcription of genes, including globin. These marks often communicate with each other and can be read by histone modification binding effectors and their associated complexes, dictating both active and repressive histone codes.
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The role of WDR5 in silencing human fetal globin gene expression
Regulation of gene expression , or gene regulation ,  includes a wide range of mechanisms that are used by cells to increase or decrease the production of specific gene products protein or RNA. Sophisticated programs of gene expression are widely observed in biology, for example to trigger developmental pathways, respond to environmental stimuli, or adapt to new food sources. Virtually any step of gene expression can be modulated, from transcriptional initiation , to RNA processing , and to the post-translational modification of a protein. Often, one gene regulator controls another, and so on, in a gene regulatory network. Gene regulation is essential for viruses , prokaryotes and eukaryotes as it increases the versatility and adaptability of an organism by allowing the cell to express protein when needed. In multicellular organisms, gene regulation drives cellular differentiation and morphogenesis in the embryo, leading to the creation of different cell types that possess different gene expression profiles from the same genome sequence. Although this does not explain how gene regulation originated, evolutionary biologists include it as a partial explanation of how evolution works at a molecular level , and it is central to the science of evolutionary developmental biology "evo-devo".
Early mouse development is accompanied by dynamic changes in chromatin modifications, including G9a-mediated histone H3 lysine 9 dimethylation H3K9me2 , which is essential for embryonic development. Here we show that genome-wide accumulation of H3K9me2 is crucial for postimplantation development, and coincides with redistribution of enhancer of zeste homolog 2 EZH2 -dependent histone H3 lysine 27 trimethylation H3K27me3. Loss of G9a or EZH2 results in upregulation of distinct gene sets involved in cell cycle regulation, germline development and embryogenesis. Notably, the H3K9me2 modification extends to active enhancer elements where it promotes developmentally-linked gene silencing and directly marks promoters and gene bodies.
It is now well established that cells modify chromatin to establish transcriptionally active or inactive chromosomal regions. Such regulation of the chromatin structure is essential for the proper development of organisms. This chapter presents an overview of recent studies on chromatin factors in C. Cell differentiation in multicellullar organisms is the consequence of the precise actions of many genes whose individual expression is temporally and spatially regulated.
The expression of transgenes in plants can be inhibited by transcriptional or posttranscriptional silencing mechanisms. There is increasing evidence that transcriptional silencing involves changes at the chromatin level, which has raised an interest in the role of chromatin organization in plant gene expression in general. This article attempts to assemble the current evidence for changes at the chromatin level being used as a mechanism for regulating transcription of transgenes and endogenous genes.
Early mouse development is accompanied by dynamic changes in chromatin modifications, including G9a-mediated histone H3 lysine 9 dimethylation H3K9me2 , which is essential for embryonic development. Here we show that genome-wide accumulation of H3K9me2 is crucial for postimplantation development, and coincides with redistribution of enhancer of zeste homolog 2 EZH2 -dependent histone H3 lysine 27 trimethylation H3K27me3. Loss of G9a or EZH2 results in upregulation of distinct gene sets involved in cell cycle regulation, germline development and embryogenesis.