Search tips
Search criteria

Results 1-25 (70)

Clipboard (0)

Select a Filter Below

more »
Year of Publication
1.  Chemical Modification-Assisted Bisulfite Sequencing (CAB-Seq) for 5-Carboxylcytosine Detection in DNA 
5-Methylcytosine (5mC) in DNA can be oxidized stepwise to 5-hydroxymethylcytosine (5hmC), 5- formylcytosine (5fC), and 5-carboxylcytosine (5caC) by the TET family proteins. Thymine DNA glycosylase can further remove 5fC and 5caC, connecting 5mC oxidation with active DNA demethylation. Here we present a chemical modification-assisted bisulfite sequencing (CAB-Seq) that can detect 5caC with single-base resolution in DNA. We optimized 1-ethyl-3- [3-dimethylaminopropyl]carbodiimide hydrochloride (EDC)- catalyzed amide bond formation between the carboxyl group of 5caC and a primary amine group. We found that the modified 5caC can survive the bisulfite treatment without deamination. Therefore, this chemical labeling coupled with bisulfite treatment provides a base-resolution detection and sequencing method for 5caC.
PMCID: PMC3727251  PMID: 23758547
2.  Genome-wide profiling of 5-formylcytosine reveals its roles in epigenetic priming 
Cell  2013;153(3):678-691.
TET proteins oxidize 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC). 5fC and 5caC are excised by mammalian DNA glycosylase TDG, implicating 5mC oxidation in DNA demethylation. Here we show that the genomic locations of 5fC can be determined by coupling chemical reduction with biotin tagging. Genome-wide mapping of 5fC in mouse embryonic stem cells (mESCs) reveals that 5fC preferentially occurs at poised enhancers among other gene regulatory elements. Application to Tdg null mESCs further suggests that 5fC production coordinates with p300 in remodeling epigenetic states of enhancers. This process, which is not influenced by 5hmC, appears to be associated with further oxidation of 5hmC and commitment to demethylation through 5fC. Finally, we resolved 5fC at base-resolution by hydroxylamine-based protection from bisulfite-mediated deamination, thereby confirming sites of 5fC accumulation. Our results reveal roles of active 5mC/5hmC oxidation and TDG-mediated demethylation in epigenetic tuning at regulatory elements.
PMCID: PMC3657391  PMID: 23602153
3.  Subtelomeric hotspots of aberrant 5-hydroxymethylcytosine-mediated epigenetic modifications during reprogramming to pluripotency 
Nature cell biology  2013;15(6):700-711.
Mammalian somatic cells can be directly reprogrammed into induced pluripotent stem cells (iPSCs) by introducing defined sets of transcription factors. Somatic cell reprogramming involves epigenomic reconfiguration, conferring iPSCs with characteristics similar to embryonic stem cells (ESCs). Human ES cells contain 5-hydroxymethylcytosine (5hmC), which is generated through the oxidation of 5-methylcytosine by the TET enzyme family. Here we show that 5hmC levels increase significantly during reprogramming to human iPSCs mainly due to TET1 activation, and this hydroxymethylation change is critical for optimal epigenetic reprogramming, but does not compromise primed pluripotency. Compared with hES cells, we find iPS cells tend to form large-scale (100 kb-1.3 Mb) aberrant reprogramming hotspots in subtelomeric regions, most of which display incomplete hydroxymethylation on CG sites. Strikingly, these 5hmC aberrant hotspots largely coincide (~80%) with aberrant iPS-ES non-CG methylation regions. Our results suggest that TET1-mediated 5hmC modification could contribute the epigenetic variation of iPSCs and iPSC-hESC differences.
PMCID: PMC3998089  PMID: 23685628
4.  A Novel Method for Fast Change-Point Detection on Simulated Time Series and Electrocardiogram Data 
PLoS ONE  2014;9(4):e93365.
Although Kolmogorov-Smirnov (KS) statistic is a widely used method, some weaknesses exist in investigating abrupt Change Point (CP) problems, e.g. it is time-consuming and invalid sometimes. To detect abrupt change from time series fast, a novel method is proposed based on Haar Wavelet (HW) and KS statistic (HWKS). First, the two Binary Search Trees (BSTs), termed TcA and TcD, are constructed by multi-level HW from a diagnosed time series; the framework of HWKS method is implemented by introducing a modified KS statistic and two search rules based on the two BSTs; and then fast CP detection is implemented by two HWKS-based algorithms. Second, the performance of HWKS is evaluated by simulated time series dataset. The simulations show that HWKS is faster, more sensitive and efficient than KS, HW, and T methods. Last, HWKS is applied to analyze the electrocardiogram (ECG) time series, the experiment results show that the proposed method can find abrupt change from ECG segment with maximal data fluctuation more quickly and efficiently, and it is very helpful to inspect and diagnose the different state of health from a patient's ECG signal.
PMCID: PMC3972110  PMID: 24690633
5.  High-yield novel leech hyaluronidase to expedite the preparation of specific hyaluronan oligomers 
Scientific Reports  2014;4:4471.
Hyaluronidases (HAases), particularly leech HAases, have attracted intense attention due to their broad applications in medical treatments and great potential for the enzymatic production of hyaluronan oligosaccharides. However, little is known about this third interesting family of HAases. Here, we applied the random amplification of cDNA ends polymerase chain reaction (RACE-PCR) approach to identify the first leech HAase-encoding gene. By combining protein engineering and high-density culture, we achieved high-level production (8.42 × 105 U ml−1) in the yeast Pichia pastoris secretory expression system. Compared with the commercial bovine testicular HAase, the recombinant leech HAase exhibited superior enzymatic properties. Furthermore, analysis of the hydrolytic process suggested that this novel enzyme adopts a nonprocessive endolytic mode, yielding a narrow-spectrum of specific HA oligosaccharides with different incubation times. Large-scale production of this novel leech HAase will not only greatly promote medical applications but also facilitate the enzymatic production of specific HA oligosaccharides.
PMCID: PMC3966032  PMID: 24667183
7.  Coordination of Engineered Factors with TET1/2 Promotes Early-Stage Epigenetic Modification during Somatic Cell Reprogramming 
Stem Cell Reports  2014;2(3):253-261.
Somatic cell reprogramming toward induced pluripotent stem cells (iPSCs) holds great promise in future regenerative medicine. However, the reprogramming process mediated by the traditional defined factors (OSMK) is slow and extremely inefficient. Here, we develop a combination of modified reprogramming factors (OySyNyK) in which the transactivation domain of the Yes-associated protein is fused to defined factors and establish a highly efficient and rapid reprogramming system. We show that the efficiency of OySyNyK-induced iPSCs is up to 100-fold higher than the OSNK and the reprogramming by OySyNyK is very rapid and is initiated in 24 hr. We find that OySyNyK factors significantly increase Tet1 expression at the early stage and interact with Tet1/2 to promote reprogramming. Our studies not only establish a rapid and highly efficient iPSC reprogramming system but also uncover a mechanism by which engineered factors coordinate with TETs to regulate 5hmC-mediated epigenetic control.
Graphical Abstract
•A combination of modified reprogramming factors (OySyNyK) is developed•A highly efficient and rapid reprogramming system is established•TET1/2 proteins are involved in rapid iPSC induction by OySyNyK•OySyNyK factors coordinate with TET proteins to promote rapid reprogramming
The reprogramming process mediated by the traditional defined factors (OSMK) is slow and inefficient. Sun, Jin, Chen, and colleagues have developed a combination of modified reprogramming factors (OySyNyK) in which the transactivation domain of the Yes-associated protein is fused to defined factors and establish a highly efficient and rapid reprogramming system.
PMCID: PMC3964280  PMID: 24672749
8.  Identifying Bipolar Disorder Susceptibility Loci in a Densely Affected Pedigree 
Molecular psychiatry  2012;18(12):1245-1246.
PMCID: PMC3899577  PMID: 23247078
Bipolar disorder; genetics; genome-wide association; copy number variation; whole genome sequencing; exome sequencing; rare variation
9.  Genome-wide DNA hydroxymethylation changes are associated with neurodevelopmental genes in the developing human cerebellum 
Human Molecular Genetics  2012;21(26):5500-5510.
5-Hydroxymethylcytosine (5-hmC) is a newly discovered modified form of cytosine that has been suspected to be an important epigenetic modification in neurodevelopment. While DNA methylation dynamics have already been implicated during neurodevelopment, little is known about hydroxymethylation in this process. Here, we report DNA hydroxymethylation dynamics during cerebellum development in the human brain. Overall, we find a positive correlation between 5-hmC levels and cerebellum development. Genome-wide profiling reveals that 5-hmC is highly enriched on specific gene regions including exons and especially the untranslated regions (UTRs), but it is depleted on introns and intergenic regions. Furthermore, we have identified fetus-specific and adult-specific differentially hydroxymethylated regions (DhMRs), most of which overlap with genes and CpG island shores. Surprisingly, during development, DhMRs are highly enriched in genes encoding mRNAs that can be regulated by fragile X mental retardation protein (FMRP), some of which are disrupted in autism, as well as in many known autism genes. Our results suggest that 5-hmC-mediated epigenetic regulation may broadly impact the development of the human brain, and its dysregulation could contribute to the molecular pathogenesis of neurodevelopmental disorders.
Accession number: Sequencing data have been deposited to GEO with accession number GSE40539.
PMCID: PMC3516134  PMID: 23042784
10.  Cell-Cycle Control of Developmentally Regulated Transcription Factors Accounts for Heterogeneity in Human Pluripotent Cells 
Stem Cell Reports  2013;1(6):532-544.
Heterogeneity within pluripotent stem cell (PSC) populations is indicative of dynamic changes that occur when cells drift between different states. Although the role of metastability in PSCs is unclear, it appears to reflect heterogeneity in cell signaling. Using the Fucci cell-cycle indicator system, we show that elevated expression of developmental regulators in G1 is a major determinant of heterogeneity in human embryonic stem cells. Although signaling pathways remain active throughout the cell cycle, their contribution to heterogeneous gene expression is restricted to G1. Surprisingly, we identify dramatic changes in the levels of global 5-hydroxymethylcytosine, an unanticipated source of epigenetic heterogeneity that is tightly linked to cell-cycle progression and the expression of developmental regulators. When we evaluated gene expression in differentiating cells, we found that cell-cycle regulation of developmental regulators was maintained during lineage specification. Cell-cycle regulation of developmentally regulated transcription factors is therefore an inherent feature of the mechanisms underpinning differentiation.
•Embryonic stem cells are lineage primed in G1•Transcription of developmentally regulated genes is cell-cycle regulated•5hmC is cell-cycle regulated•Stem cells initiate differentiation from G1
Pluripotent stem cell heterogeneity has been attributed to stochastic variations in signaling pathways across the population. Using Fucci cell-cycle reporters, Dalton and colleagues show that stem cell “lineage priming” in G1 is associated with cell-cycle-dependent changes in the transcription of developmentally regulated genes. Moreover, these changes are paralleled by levels of the epigenetic mark 5-hydroxymethylcytosine. These findings identify the cell cycle as major source of heterogeneity in human pluripotent stem cells.
PMCID: PMC3871385  PMID: 24371808
11.  Fragile X premutation RNA is sufficient to cause primary ovarian insufficiency in mice 
Human Molecular Genetics  2012;21(23):5039-5047.
Spontaneous 46,XX primary ovarian insufficiency (POI), also known as ‘premature menopause’ or ‘premature ovarian failure’, refers to ovarian dysfunction that results in a range of abnormalities, from infertility to early menopause as the end stage. The most common known genetic cause of POI is the expansion of a CGG repeat to 55–199 copies (premutation) in the 5′ untranslated region in the X-linked fragile X mental retardation 1 (FMR1) gene. POI associated with the FMR1 premutation is referred to as fragile X-associated POI (FXPOI). Here, we characterize a mouse model carrying the human FMR1 premutation allele and show that FMR1 premutation RNA can cause a reduction in the number of growing follicles in ovaries and is sufficient to impair female fertility. Alterations in selective serum hormone levels, including FSH, LH and 17β-estradiol, are seen in this mouse model, which mimics findings in humans. In addition, we also find that LH-induced ovulation-related gene expression is specifically altered. Finally, we show that the FMR1 premutation allele can lead to reduced phosphorylation of Akt and mTOR proteins. These results together suggest that FMR1 premutation RNA could cause the POI associated with FMR1 premutation carriers, and the Akt/mTOR pathway may serve as a therapeutic target for FXPOI.
PMCID: PMC3490511  PMID: 22914733
12.  Epigenetics-Based Therapeutics for Neurodegenerative Disorders 
Epigenetic regulation, such as DNA methylation and histone modification, is implicated in the aberrant changes in gene expression that occur during the progression of neurodegeneration. Many epigenetics-based drugs have been developed recently for the treatment of some neurodegenerative disorders, including Alzheimer’s, Parkinson’s, and Huntington’s diseases. Here we review recent studies that highlight the role of epigenetic modifications in neurodegeneration, among them DNA methylation and demethylation and histone acetylation and deacetylation; we also explore the possibility of using epigenetics-based therapeutics to treat neurodegenerative disorders.
PMCID: PMC3601938  PMID: 23526405
DNA methylation; DNA demethylation; Neurodegeneration; Therapeutics; DNMT inhibitors; HDAC inhibitors; Histone acetylation; Alzheimer’s disease; Parkinson’s disease; Huntington’s disease; Amyotrophic lateral sclerosis
13.  Cystoscopic Extraction Technique and External Drainage Rescue of a Failed Attempt to Traverse a Severe Transplanted Ureteral Obstruction 
Korean Journal of Urology  2013;54(12):876-880.
The aim of this research was to evaluate the efficacy of the cystoscopic extraction and external drainage techniques for unsuccessful antegrade stenting in transplanted severe ureteral obstruction.
Materials and Methods
A total of 26 patients with severe transplanted ureteral obstruction in whom the cystoscopic extraction technique and/or external drainage technique was performed were retrospectively evaluated. After the severe obstruction was successfully traversed, balloon dilatation followed by double-J stent insertion was performed.
Of the 26 patients (male:female, 9:4; mean age, 38.1 years) who underwent failed ureteral stenting with the conventional procedure, 16 patients underwent successful stenting with the cystoscopic extraction technique, and 10 patients underwent successful stenting following external drainage. The mean serum creatinine of the 26 patients before stenting was 42.9 mg/dL (range, 32.7 to 54.1 mg/dL), which decreased to 10.3 mg/dL (range, 8.7 to 11.8 mg/dL) after stenting. The complications of the procedure were lower abdominal pain in 22 patients and gross hematuria in 9 patients. All complications were relieved with medical care within 3 to 5 days after the procedure. No major complications occurred.
The cystoscopic extraction technique and external drainage technique are safe and useful for traversing a severe transplanted ureteral obstruction after a failed conventional procedure.
PMCID: PMC3866293  PMID: 24363871
Cystoscopes; Drainage; Stents; Transplantation; Ureteral obstruction
14.  Phosphoglycerate mutase 1 coordinates glycolysis and biosynthesis to promote tumor growth 
Cancer cell  2012;22(5):585-600.
It remains unclear how cancer cells coordinate glycolysis and biosynthesis to support rapidly growing tumors. We found that glycolytic enzyme phosphoglycerate mutase 1 (PGAM1), commonly upregulated in human cancers due to loss of TP53, contributes to biosynthesis regulation in part by controlling intracellular levels of its substrate 3-phosphoglycerate (3-PG) and product 2-phosphoglycerate (2-PG). 3-PG binds to and inhibits 6-phosphogluconate dehydrogenase in the oxidative pentose phosphate pathway (PPP), while 2-PG activates 3-phosphoglycerate dehydrogenase to provide feedback control of 3-PG levels. Inhibition of PGAM1 by shRNA or a small molecule inhibitor PGMI-004A results in increased 3-PG and decreased 2-PG levels in cancer cells, leading to significantly decreased glycolysis, PPP flux and biosynthesis, as well as attenuated cell proliferation and tumor growth.
PMCID: PMC3500524  PMID: 23153533
15.  Activated boron nitride as an effective adsorbent for metal ions and organic pollutants 
Scientific Reports  2013;3:3208.
Novel activated boron nitride (BN) as an effective adsorbent for pollutants in water and air has been reported in the present work. The activated BN was synthesized by a simple structure-directed method that enabled us to control the surface area, pore volume, crystal defects and surface groups. The obtained BN exhibits an super high surface area of 2078 m2/g, a large pore volume of 1.66 cm3/g and a special multimodal microporous/mesoporous structure located at ~ 1.3, ~ 2.7, and ~ 3.9 nm, respectively. More importantly, the novel activated BN exhibits an excellent adsorption performance for various metal ions (Cr3+, Co2+, Ni2+, Ce3+, Pb2+) and organic pollutants (tetracycline, methyl orange and congo red) in water, as well as volatile organic compounds (benzene) in air. The excellent reusability of the activated BN has also been confirmed. All the features render the activated BN a promising material suitable for environmental remediation.
PMCID: PMC3826095  PMID: 24220570
16.  Dynamics of DNA Methylation in Aging and Alzheimer's Disease 
DNA and Cell Biology  2012;31(Suppl 1):S-42-S-48.
Gene expression is modulated by epigenetic factors that come in varying forms, such as DNA methylation, histone modifications, microRNAs, and long noncoding RNAs. Recent studies reveal that these epigenetic marks are important regulatory factors in brain function. In particular, DNA methylation dynamics are found to be essential components of epigenetic regulation in the mammalian central nervous system. In this review, we provide an overview of the literature on DNA methylation in neurodegenerative diseases, with a special focus on methylation of 5-position of cytosine base (5mC) and hydroxymethylation of 5-position of cytosine base (5hmC) in the context of neurodegeneration associated with aging and Alzheimer's disease.
PMCID: PMC3461976  PMID: 22313030
17.  Stable Isotope Labeling with Amino Acids in Drosophila for Quantifying Proteins and Modifications 
Journal of proteome research  2012;11(9):4403-4412.
Drosophila melanogaster is a common animal model for genetics studies, and quantitative proteomics studies of the fly are emerging. Here we present in detail the development of a procedure to incorporate stable isotope labeled amino acids into the fly proteome. In the method of Stable Isotope Labeling with Amino acids in Drosophila melanogaster (SILAC fly), flies were fed with SILAC labeled yeast grown with modified media, enabling near complete labeling in a single generation. Biological variation in proteome among individual flies was evaluated in a series of null experiments. We further applied the SILAC fly method to profile proteins from a model of fragile X syndrome, the most common cause of inherited mental retardation in human. The analysis identified a number of altered proteins in the disease model, including actin-binding protein profilin and microtubulin-associated protein futsch. The change of both proteins was validated by immunoblotting analysis. Moreover, we extended the SILAC fly strategy to study the dynamics of protein ubiquitination during the fly life span (from day 1 to day 30), by measuring the level of ubiquitin along with two major polyubiquitin chains (K48 and K63 linkages). The results show that the abundance of protein ubiquitination and the two major linkages do not change significantly within the measured age range. Together, the data demonstrate the application of the SILAC principle in Drosophila melanogaster, facilitating the integration of powerful fly genomics with emerging proteomics.
PMCID: PMC3443408  PMID: 22830426
SILAC; Drosophila melanogaster; proteomics; mass spectrometry; fragile X syndrome; ubiquitin
18.  Cadmium is a potent inhibitor of PPM phosphatases and targets the M1 binding site 
Scientific Reports  2013;3:2333.
The heavy metal cadmium is a non-degradable pollutant. By screening the effects of a panel of metal ions on the phosphatase activity, we unexpectedly identified cadmium as a potent inhibitor of PPM1A and PPM1G. In contrast, low micromolar concentrations of cadmium did not inhibit PP1 or tyrosine phosphatases. Kinetic studies revealed that cadmium inhibits PPM phosphatases through the M1 metal ion binding site. In particular, the negative charged D441 in PPM1G specific recognized cadmium. Our results suggest that cadmium is likely a potent inhibitor of most PPM family members except for PHLPPs. Furthermore, we demonstrated that cadmium inhibits PPM1A-regulated MAPK signaling and PPM1G-regulated AKT signaling potently in vivo. Cadmium reversed PPM1A-induced cell cycle arrest and cadmium insensitive PPM1A mutant rescued cadmium induced cell death. Taken together, these findings provide a better understanding of the effects of the toxicity of cadmium in the contexts of human physiology and pathology.
PMCID: PMC3730172  PMID: 23903585
19.  Tyr26 phosphorylation of PGAM1 provides a metabolic advantage to tumours by stabilizing the active conformation 
Nature communications  2013;4:1790.
How oncogenic signalling coordinates glycolysis and anabolic biosynthesis in cancer cells remains unclear. We recently reported that the glycolytic enzyme phosphoglycerate mutase 1 (PGAM1) regulates anabolic biosynthesis by controlling intracellular levels of its substrate 3-phosphoglycerate (3-PG) and product 2-phosphoglycerate (2-PG). Here we report a novel mechanism in which Y26 phosphorylation enhances PGAM1 activation through release of inhibitory E19 that blocks the active site, stabilising cofactor 2,3-bisphosphoglycerate binding and H11 phosphorylation. We also report the crystal structure of H11-phosphorylated PGAM1 and find that phospho-H11 activates PGAM1 at least in part by promoting substrate 3-PG binding. Moreover, Y26-phosphorylation of PGAM1 is common in human cancer cells and contributes to regulation of 3-PG and 2-PG levels, promoting cancer cell proliferation and tumour growth. Since PGAM1 as a negative transcription target of TP53 is commonly upregulated in human cancers, these findings suggest that Y26 phosphorylation represents an additional acute mechanism underlying PGAM1 upregulation.
PMCID: PMC3648882  PMID: 23653202
20.  RNA-mediated neurodegeneration in fragile X-associated tremor/ataxia syndrome 
Brain Research  2012;1462:112-117.
Carriers of fragile X syndrome (FXS) have FMR1 alleles, called premutations, with a number of 5’-untranslated CGG repeats somewhere between patients, who have over 200 repeats, and normal individuals, with fewer than 60 repeats. Fragile X-associated tremor/ataxia syndrome (FXTAS), a late-onset neurodegenerative disorder, has been recognized in older male fragile X premutation carriers, and FXTAS is uncoupled from the neurodevelopmental disorder, FXS. Several lines of evidence have led to the proposal of an RNA (fragile X premutation rCGG repeat)-mediated gain-of-function toxicity model for FXTAS, in which rCGG repeat-binding proteins (RBPs) could become functionally limited by their sequestration to lengthy rCGG repeats. In this review, we will discuss the recent progress towards understanding the molecular basis of RNA-mediated neurodegeneration in FXTAS.
PMCID: PMC3372578  PMID: 22459047
21.  Colorectal cancer screening with fecal occult blood test: A 22-year cohort study 
Oncology Letters  2013;6(2):576-582.
The aim of the present study was to investigate the efficacy of colorectal cancer (CRC) screening with a three-tier fecal occult blood test (FOBT) in the Chinese population. The study was performed between 1987 and 2008 at the Beijing Military General Hospital, in a cohort of army service males and females aged >50 years. Between 1987 and 2005, a three-tier screening program, comprising guaiac-based FOBTs (gFOBTs), followed by immunochemical FOBTs for positive guaiac test samples and then colonoscopy for positive immunochemical test subjects, was performed annually. The cohort was followed up until 2008. The cohort included 5,104 subjects, of which, 3,863 subjects participated in screening (screening group) and 1,241 did not (non-screening group). The two groups did not differ in age, gender or other major risk factors for colon cancer. Overall, 36 CRCs occurred in the screening group and 21 in the non-screening group. Compared with the non-screening group, the relative risk for the incidence and mortality of CRC was 0.51 [95% confidence interval (CI), 0.30–0.87] and 0.36 (95% CI, 0.18–0.71), respectively, in the screening group. The general sensitivity of this three-tier FOBT was 80.6% (95% CI, 65.3–91.1). Thus, annual screening using the three-tier FOBT program may reduce the CRC incidence and mortality rate.
PMCID: PMC3789016  PMID: 24137374
colorectal cancer; screening; fecal occult blood test
22.  Tet-mediated covalent labelling of 5-methylcytosine for its genome-wide detection and sequencing 
Nature communications  2013;4:1517.
5-methylcytosine is an epigenetic mark that affects a broad range of biological functions in mammals. The chemically inert methyl group prevents direct labelling for subsequent affinity purification and detection. Therefore, most current approaches for the analysis of 5- methylcytosine still have limitations of being either density-biased, lacking in robustness and consistency, or incapable of analysing 5-methylcytosine specifically. Here we present an approach, TAmC-Seq, which selectively tags 5-methylcytosine with an azide functionality that can be further labelled with a biotin for affinity purification, detection and genome-wide mapping. Using this covalent labelling approach, we demonstrate high sensitivity and specificity for known methylated loci, as well as increased CpG dinucleotide coverage at lower sequencing depth as compared with antibody-based enrichment, providing an improved efficiency in the 5-methylcytosine enrichment and genome-wide profiling.
PMCID: PMC3679896  PMID: 23443545
23.  Base-Resolution Analysis of 5-Hydroxymethylcytosine in the Mammalian Genome 
Cell  2012;149(6):1368-1380.
The study of 5-hydroxylmethylcytosines (5hmC) has been hampered by the lack of a method to map it at single-base resolution on a genome-wide scale. Affinity purification-based methods cannot precisely locate 5hmC nor accurately determine its relative abundance at each modified site. We here present a genome-wide approach, Tet-assisted Bisulfite Sequencing (TAB-Seq), for mapping 5hmC at base resolution and quantifying the relative abundance of 5hmC as well as 5mC when combined with traditional bisulfite sequencing. Application of this method to embryonic stem cells not only confirms widespread distribution of 5hmC in the mammalian genome, but also reveals sequence bias and strand asymmetry at 5hmC sites. We observe high levels of 5hmC and reciprocally low levels of 5mC near but not on transcription factor binding sites. Additionally, the relative abundance of 5hmC varies significantly among distinct functional sequence elements, suggesting different mechanisms for 5hmC deposition and maintenance.
PMCID: PMC3589129  PMID: 22608086
24.  Iron Homeostasis Regulates the Activity of the MicroRNA Pathway through Poly(C)-Binding Protein 2 
Cell metabolism  2012;15(6):895-904.
MicroRNAs (miRNAs) control gene expression by promoting degradation or repressing translation of target mRNAs. The components of the miRNA pathway are subject to diverse modifications that can modulate the abundance and function of miRNAs. Iron is essential for fundamental metabolic processes, and its homeostasis is tightly regulated. Here we identified iron chelators as a class of activator of the miRNA pathway that could promote the processing of miRNA precursors. We show that cytosolic iron could regulate the activity of the miRNA pathway through poly(C)-binding protein 2 (PCBP2). PCBP2 is associated with Dicer and promotes the processing of miRNA precursors. Cytosolic iron could modulate the association between PCBP2 and Dicer, as well as the multimerization of PCBP2 and its ability to bind to miRNA precursors, which can alter the processing of miRNA precursors. Our findings reveal a role of iron homeostasis in the regulation of miRNA biogenesis.
PMCID: PMC3613991  PMID: 22633452
25.  Role of noncoding RNAs in Trinucleotide repeat neurodegenerative disorders 
Experimental Neurology  2012;235(2):469-475.
Increasingly complex networks of noncoding RNAs are being found to play important and diverse roles in the regulation of gene expression throughout the genome. Many lines of evidence are linking mutations and dysregulations of noncoding RNAs to a host of human diseases, and noncoding RNAs have been implicated in the molecular pathogenesis of some neurodegenerative disorders. The expansion of trinucleotide repeats is now recognized as a major cause of neurological disorders. Here we will review our current knowledge of the proposed mechanisms behind the involvement of noncoding RNAs in the molecular pathogenesis of neurodegenerative disorders, particularly the sequestration of specific RNA-binding proteins, the regulation of antisense transcripts, and the role of the microRNA pathway in the context of known neurodegenerative disorders caused by the expansion of trinucleotide repeats.
PMCID: PMC3345102  PMID: 22309832

Results 1-25 (70)