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Histone variants: making structurally and functionally divergent nucleosomes and linkers in chromatin
Leilei SHI, Yuda FANG
Front Biol. 2011, 6 (2): 93-101.
https://doi.org/10.1007/s11515-011-1127-5
In addition to the post-translational modifications of histone proteins, emerging literature suggests that the mosaic nucleosomes formed by incorporation of various histone variants provide another mechanism for modifying chromatin structure and function. The locally defined chromatin by histone variants is involved in transcriptional regulation, DNA repair, centromere packaging, maintenance of pericentromeric heterochromatin, stress responses, temperature sensing, development, and many other biological processes. Here, we review the universal histone variants in H2A, H3 and H1 families and their roles in epigenetics.
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Conservation and divergence of the histone H2B monoubiquitination pathway from yeast to humans and plants
Ying CAO, Ligeng MA
Front Biol. 2011, 6 (2): 109-117.
https://doi.org/10.1007/s11515-011-1000-6
Histone ubiquitination plays a critical role in the regulation of transcription, and histone H2B monoubiquitination (H2Bub1) is mainly associated with transcriptional activation. Recent studies in yeast, humans, and BoldItalic have revealed the conservation of chromatin modification via H2Bub1 during evolution. Rad6-Bre1 and their homologs are responsible for H2B monoubiquitination in diverse eukaryotic organisms, and the PAF complex is required for H2Bub1 to proceed. H2Bub1 is involved in many developmental processes in yeast, humans, and BoldItalic, and it activates gene transcription by regulating the H3K4 methylation state. Notably, the level of H3K4 methylation is entirely dependent on H2Bub1 in yeast and humans, whereas the H3K4 methylation level of only a small number of genes in BoldItalic is dependent on H2Bub1. In this review, we summarize the enzymes involved in H2B monoubiquitination and deubiquitination, and discuss the biologic functions of H2Bub1 in different organisms. In addition, we focus on recent advances in our understanding of the molecular mechanisms that enable H2Bub1 to perform its function.
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The plant Mediator and its role in noncoding RNA production
Yun Ju KIM, Xuemei CHEN
Front Biol. 2011, 6 (2): 125-132.
https://doi.org/10.1007/s11515-011-1133-7
Mediator, a conserved multiprotein complex in animals, plants, and fungi, is a cofactor of RNA polymerase II (Pol II). It is known to promote basal Pol II-mediated transcription as well as bridge sequence-specific transcriptional regulators and Pol II to integrate regulatory information. Pol II transcribes not only protein-coding genes but also intergenic regions to generate noncoding RNAs such as small RNAs (microRNAs and small interfering RNAs) and long noncoding RNAs. Intriguingly, two plant-specific polymerases, Pol IV and Pol V, have evolved from Pol II and play a role in the production of small interfering RNAs and long noncoding RNAs at heterochromatic regions to maintain genome stability through transcriptional gene silencing (TGS). Recent studies have defined the composition of the plant Mediator and evaluated its role in noncoding RNA production in relationship to Pol II, Pol IV and Pol V. Here, we review the functions of Mediator and that of noncoding RNAs generated by Pol II, Pol IV and Pol V in plants, and discuss a role of Mediator in epigenetic regulation via noncoding RNA production.
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MicroRNA-mediated DNA methylation in plants
Xiaoyun JIA, Jun YAN, Guiliang TANG
Front Biol. 2011, 6 (2): 133-139.
https://doi.org/10.1007/s11515-011-1136-4
DNA methylation, a major event in epigenetics, plays an essential role in the control of gene expression. Increasing evidence suggests that long and short non-coding RNAs are involved extensively in plants to direct the establishment, spread, and removal of DNA cytosine methylation throughout their genomes. Yet, little has been known about the role of microRNAs (miRNAs) in DNA methylation although the role of small interfering RNAs (siRNAs) in DNA methylation has been well established. Several recent studies, however, provided the evidence for miRNA-directed DNA methylation in plants, and the working mechanisms still need to be fully explored. In this review, we highlight the key features of miRNA-directed DNA methylation in plants and provide insight into the complexities of such an event in plants. The interaction between miRNAs and the epigenetic machinery and the future potential research questions are briefly discussed.
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Mobile silencing in plants: what is the signal and what defines the target
Dacheng LIANG, E. Jean FINNEGAN, Elizebeth S. DENNIS, Peter M. WATERHOUSE, Ming-Bo WANG
Front Biol. 2011, 6 (2): 140-146.
https://doi.org/10.1007/s11515-011-1145-3
RNA-mediated silencing in plants can spread from cell to cell and over a long distance, and such mobile silencing has been extensively studied in the past decade. However, major questions remain as to what is the exact nature of the mobile silencing signals, how the components of the RNA-directed DNA methylation pathway are involved, and why systemic spread of silencing has only been observed for transgenes but not endogenous genes. In this review, we provide an overview of the current knowledge on mobile gene silencing in plants and present a model where systemic silencing involves long nuclear RNA transcripts that serve as a template to amplify primary siRNA signals.
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The spindle assembly checkpoint: perspectives in tumorigenesis and cancer therapy
Joana BARBOSA, Ana Vanessa NASCIMENTO, Juliana FARIA, Patrícia SILVA, Hassan BOUSBAA
Front Biol. 2011, 6 (2): 147-155.
https://doi.org/10.1007/s11515-011-1122-x
Loss or gain of chromosomes, a condition known as aneuploidy, is a common feature of tumor cells and has therefore been proposed as the driving force for tumorigenesis. Such chromosomal instability can arise during mitosis as a result of mis-segregation of the duplicated sister chromatids to the two daughter cells. In normal cells, mis-segregation is usually prevented by the spindle assembly checkpoint (SAC), a sophisticated surveillance mechanism that inhibits mitotic exit until all chromosomes have successfully achieved bipolar attachment to spindle microtubules. Complete abrogation of SAC activity is lethal to normal as well as to tumor cells, as a consequence of massive chromosome mis-segregation. Importantly, many human aneuploid tumor cells exhibit a weakened SAC activity that allows them to tolerate gains or losses of a small number of chromosomes; and interfering with this SAC residual activity may constitute a suitable strategy to kill cancer cells. This review focuses on the potential link between SAC and tumorigenesis, and the therapeutic strategy to target the SAC for cancer treatment.
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Kinases and glutathione transferases: selective and sensitive targeting
Yasemin G. ISGOR, Belgin S. ISGOR
Front Biol. 2011, 6 (2): 156-169.
https://doi.org/10.1007/s11515-011-1112-z
Kinases, representing almost 500 proteins in the human genome, are responsible for catalyzing the phosphorylation reaction of amino acid residues at their targets. As the largest family of kinases, the protein tyrosine kinases (PTKs) have roles in controlling the essential cellular activities, and their deregulation is generally related to pathologic conditions. The recent efforts on identifying their signal transducer or mediator role in cellular signaling revealed the interaction of PTKs with numerous enzymes of different classes, such as Ser/Thr kinases (STKs), glutathione transferases (GSTs), and receptor tyrosine kinases (RTKs). In either regulation or enhancing the signaling, PTKs are determined in close interaction with these enzymes, under specific cellular conditions, such as oxidative stress and inflammation. In this concept, intensive research on thiol metabolizing enzymes recently showed their involvement in the physiologic functions in cellular signaling besides their well known traditional role in antioxidant defense. The shared signaling components between PTK and GST family enzymes will be discussed in depth in this research review to evaluate the results of recent studies important in drug targeting for therapeutic intervention, such as cell viability, migration, differentiation and proliferation.
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11 articles
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