Chunxiao Song selected recent publications
BACKGROUND: Plasma cell-free RNA (cfRNA) encompasses a broad spectrum of RNA species that can be derived from both human cells and microbes. Because cfRNA is fragmented and of low concentration, it has been challenging to profile its transcriptome using standard RNA-seq methods. METHODS: We assessed several recently developed RNA-seq methods on cfRNA samples. We then analyzed the dynamic changes of both the human transcriptome and the microbiome of plasma during pregnancy from 60 women. RESULTS: cfRNA reflects a well-orchestrated immune modulation during pregnancy: an up-regulation of antiinflammatory genes and an increased abundance of antimicrobial genes. We observed that the plasma microbiome remained relatively stable during pregnancy. The bacteria Ureaplasma shows an increased prevalence and increased abundance at postpartum, which is likely to be associated with postpartum infection. We demonstrated that cfRNA-seq can be used to monitor viral infections. We detected a number of human pathogens in our patients, including an undiagnosed patient with a high load of human parvovirus B19 virus (B19V), which is known to be a potential cause of complications in pregnancy. CONCLUSIONS: Plasma cfRNA-seq demonstrates the potential to simultaneously monitor immune response and microbial infections during pregnancy.
5-Hydroxymethylcytosine (5hmC) is an important mammalian DNA epigenetic modification that has been linked to gene regulation and cancer pathogenesis. Here we explored the diagnostic potential of 5hmC in circulating cell-free DNA (cfDNA) using a sensitive chemical labeling-based low-input shotgun sequencing approach. We sequenced cell-free 5hmC from 49 patients of seven different cancer types and found distinct features that could be used to predict cancer types and stages with high accuracy. Specifically, we discovered that lung cancer leads to a progressive global loss of 5hmC in cfDNA, whereas hepatocellular carcinoma and pancreatic cancer lead to disease-specific changes in the cell-free hydroxymethylome. Our proof-of-principle results suggest that cell-free 5hmC signatures may potentially be used not only to identify cancer types but also to track tumor stage in some cancers.
We here review primary methods used in quantifying and mapping 5-hydroxymethylcytosine (5hmC), including global quantification, restriction enzyme-based detection, and methods involving DNA-enrichment strategies and the genome-wide sequencing of 5hmC. As discovered in the mammalian genome in 2009, 5hmC, oxidized from 5-methylcytosine (5mC) by ten-eleven translocation (TET) dioxygenases, is increasingly being recognized as a biomarker in biological processes from development to pathogenesis, as its various detection methods have shown. We focus in particular on an ultrasensitive single-molecule imaging technique that can detect and quantify 5hmC from trace samples and thus offer information regarding the distance-based relationship between 5hmC and 5mC when used in combination with fluorescence resonance energy transfer.
Forkhead box A1 (FOXA1) is an FKHD family protein that plays pioneering roles in lineage-specific enhancer activation and gene transcription. Through genome-wide location analyses, here we show that FOXA1 expression and occupancy are, in turn, required for the maintenance of these epigenetic signatures, namely DNA hypomethylation and histone 3 lysine 4 methylation. Mechanistically, this involves TET1, a 5-methylcytosine dioxygenase. We found that FOXA1 induces TET1 expression via direct binding to its cis-regulatory elements. Further, FOXA1 physically interacts with the TET1 protein through its CXXC domain. TET1 thus co-occupies FOXA1-dependent enhancers and mediates local DNA demethylation and concomitant histone 3 lysine 4 methylation, further potentiating FOXA1 recruitment. Consequently, FOXA1 binding events are markedly reduced following TET1 depletion. Together, our results suggest that FOXA1 is not only able to recognize but also remodel the epigenetic signatures at lineage-specific enhancers, which is mediated, at least in part, by a feed-forward regulatory loop between FOXA1 and TET1.
The modifications 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) are the two major DNA epigenetic modifications in mammalian genomes and play crucial roles in development and pathogenesis. Little is known about the colocalization or potential correlation of these two modifications. Here we present an ultrasensitive single-molecule imaging technology capable of detecting and quantifying 5hmC and 5mC from trace amounts of DNA. We used this approach to perform single-molecule fluorescence resonance energy transfer (smFRET) experiments which measure the proximity between 5mC and 5hmC in the same DNA molecule. Our results reveal high levels of adjacent and opposing methylated and hydroxymethylated CpG sites (5hmC/5mCpGs) in mouse genomic DNA across multiple tissues. This identifies the previously undetectable and unappreciated 5hmC/5mCpGs as one of the major states for 5hmC in the mammalian genome and suggest that they could function in promoting gene expression.
Expression of functionally important genes is often tightly regulated at both transcriptional and post-transcriptional levels. We reported previously that TET1, the founding member of the TET methylcytosine dioxygenase family, plays an essential oncogenic role in MLL-rearranged acute myeloid leukemia (AML), where it is overexpressed owing to MLL-fusion-mediated direct up-regulation at the transcriptional level. Here we show that the overexpression of TET1 in MLL-rearranged AML also relies on the down-regulation of miR-26a, which directly negatively regulates TET1 expression at the post-transcriptional level. Through inhibiting expression of TET1 and its downstream targets, forced expression of miR-26a significantly suppresses the growth/viability of human MLL-rearranged AML cells, and substantially inhibits MLL-fusion-mediated mouse hematopoietic cell transformation and leukemogenesis. Moreover, c-Myc, an oncogenic transcription factor up-regulated in MLL-rearranged AML, mediates the suppression of miR-26a expression at the transcriptional level. Collectively, our data reveal a previously unappreciated signaling pathway involving the MLL-fusion/MYC⊣miR-26a⊣TET1 signaling circuit, in which miR-26a functions as an essential tumor-suppressor mediator and its transcriptional repression is required for the overexpression and oncogenic function of TET1 in MLL-rearranged AML. Thus, restoration of miR-26a expression/function holds therapeutic potential to treat MLL-rearranged AML.
How DNA demethylation is achieved in mammals is still under extensive investigation. One proposed mechanism is deamination of 5-hydroxymethylcytosine to form 5-hydroxymethyluracil (5hmU), followed by base excision repair to replace the mismatched 5hmU with cytosine. In this process, 5hmU:G mispair serves as a key intermediate and its localization and distribution in mammalian genome could be important information to investigate the proposed pathway. Here we describe a selective labeling method to map mismatched 5hmU. After converting other cytosine modifications to 5-carboxylcytosines, a biotin tag is installed onto mismatched 5hmU through β-glucosyltransferase-catalyzed glucosylation and click chemistry. The enriched 5hmU-containing DNA fragments can be subject to subsequent sequencing to reveal the distribution of 5hmU:G mispair with base-resolution information acquired.
Cell Res, 25 (3), pp. 386-389. | Citations: 34 (Scopus) | Read more2015. Base-resolution maps of 5-formylcytosine and 5-carboxylcytosine reveal genome-wide DNA demethylation dynamics.
ENDOCRINE REVIEWS, 35 (3),2014. TET1-Mediated DNA Demethylation and Epigenomic Regulation in Prostate Cancer
Hematopoietic stem cell differentiation involves the silencing of self-renewal genes and induction of a specific transcriptional program. Identification of multiple covalent cytosine modifications raises the question of how these derivatized bases influence stem cell commitment. Using a replicative primary human hematopoietic stem/progenitor cell differentiation system, we demonstrate dynamic changes of 5-hydroxymethylcytosine (5-hmC) during stem cell commitment and differentiation to the erythroid lineage. Genomic loci that maintain or gain 5-hmC density throughout erythroid differentiation contain binding sites for erythroid transcription factors and several factors not previously recognized as erythroid-specific factors. The functional importance of 5-hmC was demonstrated by impaired erythroid differentiation, with augmentation of myeloid potential, and disrupted 5-hmC patterning in leukemia patient-derived CD34+ stem/early progenitor cells with TET methylcytosine dioxygenase 2 (TET2) mutations. Thus, chemical conjugation and affinity purification of 5-hmC-enriched sequences followed by sequencing serve as resources for deciphering functional implications for gene expression during stem cell commitment and differentiation along a particular lineage.
Total publications on this page: 10
Total citations for publications on this page: 137