DNA Conformation Induces Adaptable Binding by Tandem Zinc Finger Proteins.

Tandem zinc finger (ZF) proteins are the largest and most rapidly diverging family of DNA-binding transcription regulators in mammals. ZFP568 represses a transcript of placental-specific insulin like growth factor 2 (Igf2-P0) in mice. ZFP568 binds a 24-base pair sequence-specific element upstream of Igf2-P0 via the eleven-ZF array. Both DNA and protein conformations deviate from the conventional one finger-three bases recognition, with individual ZFs contacting 2, 3, or 4 bases and recognizing thymine on the opposite strand. These interactions arise from a shortened minor groove caused by an AT-rich stretch, suggesting adaptability of ZF arrays to sequence variations. Despite conservation in mammals, mutations at Igf2 and ZFP568 reduce their binding affinity in chimpanzee and humans. Our studies provide important insights into the evolutionary and structural dynamics of ZF-DNA interactions that play a key role in mammalian development and evolution.

TFEB safeguards trophoblast syncytialization in humans and mice.

Nutrient sensing and adaptation in the placenta are essential for pregnancy viability and proper fetal growth. Our recent study demonstrated that the placenta adapts to nutrient insufficiency through mechanistic target of rapamycin (mTOR) inhibition-mediated trophoblast differentiation toward syncytiotrophoblasts (STBs), a highly specialized multinucleated trophoblast subtype mediating extensive maternal-fetal interactions. However, the underlying mechanism remains elusive. Here, we unravel the indispensable role of the mTORC1 downstream transcriptional factor TFEB in STB formation both in vitro and in vivo. TFEB deficiency significantly impaired STB differentiation in human trophoblasts and placenta organoids. Consistently, systemic or trophoblast-specific deletion of Tfeb compromised STB formation and placental vascular construction, leading to severe embryonic lethality. Mechanistically, TFEB conferred direct transcriptional activation of the fusogen ERVFRD-1 in human trophoblasts and thereby promoted STB formation, independent of its canonical function as a master regulator of the autophagy-lysosomal pathway. Moreover, we demonstrated that TFEB directed the trophoblast syncytialization response driven by mTOR complex 1 (mTORC1) signaling. TFEB expression positively correlated with the reinforced trophoblast syncytialization in human fetal growth-restricted placentas exhibiting suppressed mTORC1 activity. Our findings substantiate that the TFEB-fusogen axis ensures proper STB formation during placenta development and under nutrient stress, shedding light on TFEB as a mechanistic link between nutrient-sensing machinery and trophoblast differentiation.

Regulation of endogenous retrovirus-derived regulatory elements by GATA2/3 and MSX2 in human trophoblast stem cells.

The placenta is an organ with extraordinary phenotypic diversity in eutherian mammals. Recent evidence suggests that numerous human placental enhancers are evolved from lineage-specific insertions of endogenous retroviruses (ERVs), yet the transcription factors (TFs) underlying their regulation remain largely elusive. Here, by first focusing on MER41, a primate-specific ERV family previously linked to placenta and innate immunity, we uncover the binding motifs of multiple crucial trophoblast TFs (GATA2/3, MSX2, GRHL2) in addition to innate immunity TFs STAT1 and IRF1. Integration of ChIP-seq data confirms the binding of GATA2/3, MSX2, and their related factors on the majority of MER41-derived enhancers in human trophoblast stem cells (TSCs). MER41-derived enhancers that are constitutively active in human TSCs are distinct from those activated upon interferon stimulation, which is determined by the binding of relevant TFs and their subfamily compositions. We further demonstrate that GATA2/3 and MSX2 have prevalent binding to numerous other ERV families - indicating their broad impact on ERV-derived enhancers. Functionally, the derepression of many syncytiotrophoblast genes after MSX2 knockdown is likely to be mediated by regulatory elements derived from ERVs - suggesting ERVs are also important for mediating transcriptional repression. Overall, this study characterizes the regulation of ERV-derived regulatory elements by GATA2/3, MSX2, and their cofactors in human TSCs, and provides mechanistic insights into the importance of ERVs in human trophoblast regulatory network.

TEENA: an integrated web server for transposable element enrichment analysis in various model and non-model organisms.

Transposable elements (TEs) are abundant in the genomes of various eukaryote organisms. Increasing evidence suggests that TEs can play crucial regulatory roles-usually by creating cis-elements (e.g. enhancers and promoters) bound by distinct transcription factors (TFs). TE-derived cis-elements have gained unprecedented attentions recently, and one key step toward their understanding is to identify the enriched TEs in distinct genomic intervals (e.g. a set of enhancers or TF binding sites) as candidates for further study. Nevertheless, such analysis remains challenging for researchers unfamiliar with TEs or lack strong bioinformatic skills. Here, we present TEENA (Transposable Element ENrichment Analyzer) to streamline TE enrichment analysis in various organisms. It implements an optimized pipeline, hosts the genome/gene/TE annotations of almost one hundred species, and provides multiple parameters to enable its flexibility. Taking genomic interval data as the only user-supplied file, it can automatically retrieve the corresponding annotations and finish a routine analysis in a couple minutes. Multiple case studies demonstrate that it can produce highly reliable results matching previous knowledge. TEENA can be freely accessed at: https://sun-lab.yzu.edu.cn/TEENA. Due to its easy-to-use design, we expect it to facilitate the studies of the regulatory function of TEs in various model and non-model organisms.

Endogenous retrovirus-derived enhancers confer the transcriptional regulation of human trophoblast syncytialization.

Endogenous retroviruses (ERVs) have been proposed as a driving force for the evolution of the mammalian placenta, however, the contribution of ERVs to placental development and the underlying regulatory mechanism remain largely elusive. A key process of placental development is the formation of multinucleated syncytiotrophoblasts (STBs) in direct contact with maternal blood, through which constitutes the maternal-fetal interface critical for nutrient allocation, hormone production and immunological modulation during pregnancy. We delineate that ERVs profoundly rewire the transcriptional program of trophoblast syncytialization. Here, we first determined the dynamic landscape of bivalent ERV-derived enhancers with dual occupancy of H3K27ac and H3K9me3 in human trophoblast stem cells (hTSCs). We further demonstrated that enhancers overlapping several ERV families tend to exhibit increased H3K27ac and reduced H3K9me3 occupancy in STBs relative to hTSCs. Particularly, bivalent enhancers derived from the Simiiformes-specific MER50 transposons were linked to a cluster of genes important for STB formation. Importantly, deletions of MER50 elements adjacent to several STB genes, including MFSD2A and TNFAIP2, significantly attenuated their expression concomitant to compromised syncytium formation. Together, we propose that ERV-derived enhancers, MER50 specifically, fine-tune the transcriptional networks accounting for human trophoblast syncytialization, which sheds light on a novel ERV-mediated regulatory mechanism underlying placental development.

Crol contributes to PRE-mediated repression and Polycomb group proteins recruitment in Drosophila.

The Polycomb group (PcG) proteins are fundamental epigenetic regulators that control the repressive state of target genes in multicellular organisms. One of the open questions is defining the mechanisms of PcG recruitment to chromatin. In Drosophila, the crucial role in PcG recruitment is thought to belong to DNA-binding proteins associated with Polycomb response elements (PREs). However, current data suggests that not all PRE-binding factors have been identified. Here, we report the identification of the transcription factor Crooked legs (Crol) as a novel PcG recruiter. Crol is a C2H2-type Zinc Finger protein that directly binds to poly(G)-rich DNA sequences. Mutation of Crol binding sites as well as crol CRISPR/Cas9 knockout diminish the repressive activity of PREs in transgenes. Like other PRE-DNA binding proteins, Crol co-localizes with PcG proteins inside and outside of H3K27me3 domains. Crol knockout impairs the recruitment of the PRC1 subunit Polyhomeotic and the PRE-binding protein Combgap at a subset of sites. The decreased binding of PcG proteins is accompanied by dysregulated transcription of target genes. Overall, our study identified Crol as a new important player in PcG recruitment and epigenetic regulation.

LncRNA446 Regulates Tight Junctions by Inhibiting the Ubiquitinated Degradation of Alix after Porcine Epidemic Diarrhea Virus Infection.

Porcine epidemic diarrhea (PED) is a highly contagious disease, caused by porcine epidemic diarrhea virus (PEDV), which causes huge economic losses. Tight junction-associated proteins play an important role during virus infection; therefore, maintaining their integrity may be a new strategy for the prevention and treatment of PEDV. Long noncoding RNAs (lncRNAs) participate in numerous cellular functional activities, yet whether and how they regulate the intestinal barrier against viral infection remains to be elucidated. Here, we established a standard system for evaluating intestinal barrier integrity and then determined the differentially expressed lncRNAs between PEDV-infected and healthy piglets by lncRNA-seq. A total of 111 differentially expressed lncRNAs were screened, and lncRNA446 was identified due to significantly higher expression after PEDV infection. Using IPEC-J2 cells and intestinal organoids as in vitro models, we demonstrated that knockdown of lncRNA446 resulted in increased replication of PEDV, with further damage to intestinal permeability and tight junctions. Mechanistically, RNA pulldown and an RNA immunoprecipitation (RIP) assay showed that lncRNA446 directly binds to ALG-2-interacting protein X (Alix), and lncRNA446 inhibits ubiquitinated degradation of Alix mediated by TRIM25. Furthermore, Alix could bind to ZO1 and occludin and restore the expression level of the PEDV M gene and TJ proteins after lncRNA446 knockdown. Additionally, Alix knockdown and overexpression affects PEDV infection in IPEC-J2 cells. Collectively, our findings indicate that lncRNA446, by inhibiting the ubiquitinated degradation of Alix after PEDV infection, is involved in tight junction regulation. This study provides new insights into the mechanisms of intestinal barrier resistance and damage repair triggered by coronavirus. IMPORTANCE Porcine epidemic diarrhea is an acute, highly contagious enteric viral disease severely affecting the pig industry, for which current vaccines are inefficient due to the high variability of PEDV. Because PEDV infection can lead to severe injury of the intestinal epithelial barrier, which is the first line of defense, a better understanding of the related mechanisms may facilitate the development of new strategies for the prevention and treatment of PED. Here, we demonstrate that the lncRNA446 directly binds one core component of the actomyosin-tight junction complex named Alix and inhibits its ubiquitinated degradation. Functionally, the lncRNA446/Alix axis can regulate the integrity of tight junctions and potentially repair intestinal barrier injury after PEDV infection.

Improved solar-driven water purification using an eco-friendly and cost-effective aerogel-based interfacial evaporator with exceptional photocatalytic capabilities.

As a promising solution to address the global challenge of freshwater scarcity, solar-powered interfacial steam generation has undergone notable advancements. This study introduces a novel solar-driven interfacial evaporation membrane (ZnIn2S4@SiO2/ACSA, ZSAS) comprising a ZnIn2S4@SiO2 composite and a black sodium alginate aerogel infused with activated carbon. The ZSAS membrane demonstrates exceptional light absorption and thermal insulation, leading to elevated surface temperatures and reduced heat dissipation into the bulk water. Furthermore, the incorporation of AC reinforces the mechanical properties of the ZSAS membrane and enhances the water purification performance. These collective features result in an impressive evaporation rate of 1.485 kg m-2 h-1 and a high photothermal conversion efficiency of 91.2% under 1 sun irradiation for the optimal ZSAS membrane. Moreover, the optimal ZSAS membrane can effectively remove salts, heavy metal ions, and organic pollutants, benefitting from its superior evaporation separation effect and the photocatalytic properties of the ZnIn2S4@SiO2 composite.

Proteomic analysis of zebrafish folliculogenesis identifies YB-1 (Ybx1/ybx1) as a potential gatekeeping molecule controlling early ovarian folliculogenesis.

As in mammals, ovarian folliculogenesis in teleosts also consists of two phases: the primary growth (PG) and secondary growth (SG) phases, which are analogous to the preantral and antral phases respectively in mammals. In this study, we performed a proteomic analysis on zebrafish follicles undergoing the PG-SG transition aiming to identify factors involved in the event. Numerous proteins showed significant changes, and the most prominent one was Y-box binding protein 1 (YB-1; Ybx1/ybx1), a transcription factor and mRNA-binding protein. YB-1 belongs to the Y-box binding protein family, which also includes the gonad-specific YB-2. Interestingly, phylogenetic analysis showed no YB-2 homolog in zebrafish. Although ybx1 mRNA was expressed in various tissues, its protein Ybx1 was primarily produced in the gonads, similar to YB-2 in other species. In the ovary, Ybx1 protein started to appear in early follicles newly emerged from the germ cell cysts, reached the highest level in late PG oocytes, but decreased precipitously when the follicles entered the SG phase. In PG follicles, Ybx1 might function as a key component of the messenger ribonucleoprotein particles (mRNPs) in association with other RNA-binding proteins. Similar to mammalian YB-1, zebrafish Ybx1 also contains functional signals that determine its intracellular localization. In conclusion, Ybx1 may play dual roles of YB-1 and YB-2 in zebrafish. In the ovary, Ybx1 binds mRNAs to stabilize them while preventing their translation. At PG-SG transition, Ybx1 is removed to release the masked mRNAs for translation into functional proteins, leading to follicle activation.

Inhibition of EZH2 Causes Retrotransposon Derepression and Immune Activation in Porcine Lung Alveolar Macrophages.

Alveolar macrophages (AMs) form the first defense line against various respiratory pathogens, and their immune response has a profound impact on the outcome of respiratory infection. Enhancer of zeste homolog 2 (EZH2), which catalyzes the trimethylation of H3K27 for epigenetic repression, has gained increasing attention for its immune regulation function, yet its exact function in AMs remains largely obscure. Using porcine 3D4/21 AM cells as a model, we characterized the transcriptomic and epigenomic alterations after the inhibition of EZH2. We found that the inhibition of EZH2 causes transcriptional activation of numerous immune genes and inhibits the subsequent infection by influenza A virus. Interestingly, specific families of transposable elements, particularly endogenous retrovirus elements (ERVs) and LINEs which belong to retrotransposons, also become derepressed. While some of the derepressed ERV families are pig-specific, a few ancestral families are known to be under EZH2-mediated repression in humans. Given that derepression of ERVs can promote innate immune activation through "viral mimicry", we speculate that ERVs may also contribute to the coinciding immune activation in AMs after the inhibition of EZH2. Overall, this study improves the understanding of the EZH2-related immune regulation in AMs and provides novel insights into the epigenetic regulation of retrotransposons in pigs.

Endogenous Retroviruses Drive Lineage-Specific Regulatory Evolution across Primate and Rodent Placentae.

In mammals, the placenta mediates maternal-fetal nutrient and waste exchange and acts in an immunomodulatory way to facilitate maternal-fetal tolerance. The placenta is highly diverse across mammalian species, yet the molecular mechanisms that distinguish the placenta of human from other mammals are not fully understood. Using an interspecies transcriptomic comparison of human, macaque, and mouse late-gestation placentae, we identified hundreds of genes with lineage-specific expression-including dozens that are placentally enriched and potentially related to pregnancy. We further annotated the enhancers for different human tissues using epigenomic data and demonstrate that the placenta and chorion are unique in that their enhancers display the least conservation. We identified numerous lineage-specific human placental enhancers and found they highly overlap with specific families of endogenous retroviruses (ERVs), including MER21A, MER41A/B, and MER39B that were previously linked to immune response and placental function. Among these ERV families, we further demonstrate that MER41A/B insertions create dozens of lineage-specific serum response factor-binding loci in human, including one adjacent to FBN2, a placenta-specific gene with increased expression in humans that produces the peptide hormone placensin to stimulate glucose secretion and trophoblast invasion. Overall, our results demonstrate the prevalence of lineage-specific placental enhancers which are frequently associated with ERV insertions and likely facilitate the lineage-specific evolution of the mammalian placenta.

Targeted inhibition of PPARα ameliorates CLA-induced hypercholesterolemia via hepatic cholesterol biosynthesis reprogramming.

BACKGROUND & AIMS: Disruption of lipid metabolism is largely linked to metabolic disorders, such as hypercholesterolemia (HCL) and liver steatosis. While cholesterol metabolic re-programmers can serve as targets for relevant interventions. Here we explored the dietary conjugated linoleic acids (CLA)-induced HCL in mice and the molecular regulation behind it. METHODS: A high dose of CLA supplementation in the diet was used to induce HCL in mice and was found to cause a hyper-activated cholesterol biosynthesis programme in the liver, leading to cholesterol metabolism dysregulation. The effects of a small-molecule drug targeting PPARα, i.e., GW6471 were studied in vivo in mice fed diets with CLA supplementation for 28 days, and in primary hepatocytes derived from HCL-mice in vitro. RESULTS: We demonstrate that CLA induced HCL and liver steatosis through multiple pathways. Among which was the PPARα-mediated cholesterogenesis. It was found to cooperate with SREBP2 via binding to Hmgcr and Dhcr7 (genes encoding key enzymes of the cholesterol biosynthetic pathway) and recruits the histone marks H3K27ac and H3K4me1 and cofactors. PPARα inhibition disrupts its physical association with SREBP2 by blocking cobinding of PPARα and SREBP2 to the genomic DNA response element. We showed that NR RORγ functions as an essential mediator that facilitates the interaction of PPARα and SREBP2 to modulate the cholesterol biosynthesis genes expression. CONCLUSIONS: Our study unravels that the small-molecule compound GW6471 exerts an attractive therapeutic effect for CLA-induced HCL, involving multiple pathways with the "PPARα-RORγ-SREBP2" being a potential complex player in this hepatic cholesterol biosynthesis programming.

Anthropoid primate-specific retroviral element THE1B controls expression of CRH in placenta and alters gestation length.

Pregnancy and parturition are intricately regulated to ensure successful reproductive outcomes. However, the factors that control gestational length in humans and other anthropoid primates remain poorly defined. Here, we show the endogenous retroviral long terminal repeat transposon-like human element 1B (THE1B) selectively controls placental expression of corticotropin-releasing hormone (CRH) that, in turn, influences gestational length and birth timing. Placental expression of CRH and subsequently prolonged gestational length were found in two independent strains of transgenic mice carrying a 180-kb human bacterial artificial chromosome (BAC) DNA that contained the full length of CRH and extended flanking regions, including THE1B. Restricted deletion of THE1B silenced placental CRH expression and normalized birth timing in these transgenic lines. Furthermore, we revealed an interaction at the 5' insertion site of THE1B with distal-less homeobox 3 (DLX3), a transcription factor expressed in placenta. Together, these findings suggest that retroviral insertion of THE1B into the anthropoid primate genome may have initiated expression of CRH in placental syncytiotrophoblasts via DLX3 and that this placental CRH is sufficient to alter the timing of birth.

Global changes of H3K27me3 domains and Polycomb group protein distribution in the absence of recruiters Spps or Pho.

Polycomb group (PcG) proteins maintain the silenced state of key developmental genes in animals, but how these proteins are recruited to specific regions of the genome is still poorly understood. In Drosophila, PcG proteins are recruited to Polycomb response elements (PREs) that include combinations of sites for sequence specific DNA binding "PcG recruiters," including Pho, Cg, and Spps. To understand their roles in PcG recruitment, we compared Pho-, Cg-, and Spps-binding sites against H3K27me3 and key PcG proteins by ChIP-seq in wild-type and mutant third instar larvae. H3K27me3 in canonical Polycomb domains is decreased after the reduction of any recruiter. Reduction of Spps and Pho, but not Cg, causes the redistribution of H3K27me3 to heterochromatin. Regions with dramatically depleted H3K27me3 after Spps knockout are usually accompanied by decreased Pho binding, suggesting their cooperative binding. PcG recruiters, the PRC2 component E(z), and the PRC1 components Psc and Ph cobind thousands of active genes outside of H3K27me3 domains. This study demonstrates the importance of distinct PcG recruiters for the establishment of unique Polycomb domains. Different PcG recruiters can act both cooperatively and independently at specific PcG target genes, highlighting the complexity and diversity of PcG recruitment mechanisms.

Integrative single-cell omics analyses reveal epigenetic heterogeneity in mouse embryonic stem cells.

Embryonic stem cells (ESCs) consist of a population of self-renewing cells displaying extensive phenotypic and functional heterogeneity. Research towards the understanding of the epigenetic mechanisms underlying the heterogeneity among ESCs is still in its initial stage. Key issues, such as how to identify cell-subset specifically methylated loci and how to interpret the biological meanings of methylation variations remain largely unexplored. To fill in the research gap, we implemented a computational pipeline to analyze single-cell methylome and to perform an integrative analysis with single-cell transcriptome data. According to the origins of variation in DNA methylation, we determined the genomic loci associated with allelic-specific methylation or asymmetric DNA methylation, and explored a beta mixture model to infer the genomic loci exhibiting cell-subset specific methylation (CSM). We observed that the putative CSM loci in ESCs are significantly enriched in CpG island (CGI) shelves and regions with histone marks for promoter and enhancer, and the genes hosting putative CSM loci show wide-ranging expression among ESCs. More interestingly, the putative CSM loci may be clustered into co-methylated modules enriching the binding motifs of distinct sets of transcription factors. Taken together, our study provided a novel tool to explore single-cell methylome and transcriptome to reveal the underlying transcriptional regulatory networks associated with epigenetic heterogeneity of ESCs.

Identification and characterization of a specific 13-miRNA expression signature during follicle activation in the zebrafish ovary.

Ovarian folliculogenesis is always of great interest in reproductive biology. However, the molecular mechanisms that control follicle development, particularly the early phase of follicle activation or recruitment, still remain poorly understood. In an attempt to decipher the gene networks and signaling pathways involved in such transition, we conducted a transcriptomic analysis (RNA-seq) on zebrafish primary growth (PG, stage I; inactive) and previtellogenic (PV, stage II; activated) follicles. A total of 118 unique microRNAs (miRNAs) (11 downregulated and 83 upregulated during PG/PV transition) and 56711 unique messenger RNAs (mRNAs) (1839 downregulated and 7243 upregulated during PG/PV transition) were identified. Real-time quantitative polymerase chain reaction analysis confirmed differential expression of 46 miRNAs from 66 candidates (66.67%). Among which, we chose to focus on 13 miRNAs (let-7a, -7b, -7c-5p, -7d-5p, -7h, -7i; miR-21, -23a-3p, -27c-3p, -107a-3p, -125b-5p, -145-3p, and -202-5p) that exhibited significant differential expression between PG and PV follicles (P ≤ 0.045*). With this 13-miRNA expression signature alone, PG follicles can be well differentiated from PV follicles by hierarchical clustering, suggesting their functional relevance during PG-to-PV transition. By overlaying predicted target genes and the differentially expressed mRNAs revealed by the RNA-seq analysis, especially those showing reciprocal miRNA-mRNA expression patterns, we shortlisted a panel of miRNA downstream targets for luciferase reporter validation. The reporter assay confirmed the interactions of let-7i:: atg4a (P = 0.01*), miR-202-5p::c23h20orf24 (P = 0.0004***), and miR-144-5p::ybx1 (P = 0.003**), implicating these potential miRNA-mRNA gene pairs in follicle activation during folliculogenesis. Our transcriptomic data analyses suggest that miRNA-mediated post-transcriptional control may represent an important mechanism underlying follicle activation.

EBT: a statistic test identifying moderate size of significant features with balanced power and precision for genome-wide rate comparisons.

MOTIVATION: In genome-wide rate comparison studies, there is a big challenge for effective identification of an appropriate number of significant features objectively, since traditional statistical comparisons without multi-testing correction can generate a large number of false positives while multi-testing correction tremendously decreases the statistic power. RESULTS: In this study, we proposed a new exact test based on the translation of rate comparison to two binomial distributions. With modeling and real datasets, the exact binomial test (EBT) showed an advantage in balancing the statistical precision and power, by providing an appropriate size of significant features for further studies. Both correlation analysis and bootstrapping tests demonstrated that EBT is as robust as the typical rate-comparison methods, e.g. χ 2 test, Fisher's exact test and Binomial test. Performance comparison among machine learning models with features identified by different statistical tests further demonstrated the advantage of EBT. The new test was also applied to analyze the genome-wide somatic gene mutation rate difference between lung adenocarcinoma (LUAD) and lung squamous cell carcinoma (LUSC), two main lung cancer subtypes and a list of new markers were identified that could be lineage-specifically associated with carcinogenesis of LUAD and LUSC, respectively. Interestingly, three cilia genes were found selectively with high mutation rates in LUSC, possibly implying the importance of cilia dysfunction in the carcinogenesis. AVAILABILITY AND IMPLEMENTATION: An R package implementing EBT could be downloaded from the website freely: http://www.szu-bioinf.org/EBT . CONTACT: wangyj@szu.edu.cn. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

BPP: a sequence-based algorithm for branch point prediction.

MOTIVATION: Although high-throughput sequencing methods have been proposed to identify splicing branch points in the human genome, these methods can only detect a small fraction of the branch points subject to the sequencing depth, experimental cost and the expression level of the mRNA. An accurate computational model for branch point prediction is therefore an ongoing objective in human genome research. RESULTS: We here propose a novel branch point prediction algorithm that utilizes information on the branch point sequence and the polypyrimidine tract. Using experimentally validated data, we demonstrate that our proposed method outperforms existing methods. Availability and implementation: https://github.com/zhqingit/BPP. CONTACT: djguo@cuhk.edu.hk. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

Prediction of reversible disulfide based on features from local structural signatures.

BACKGROUND: Disulfide bonds are traditionally considered to play only structural roles. In recent years, increasing evidence suggests that the disulfide proteome is made up of structural disulfides and reversible disulfides. Unlike structural disulfides, reversible disulfides are usually of important functional roles and may serve as redox switches. Interestingly, only specific disulfide bonds are reversible while others are not. However, whether reversible disulfides can be predicted based on structural information remains largely unknown. METHODS: In this study, two datasets with both types of disulfides were compiled using independent approaches. By comparison of various features extracted from the local structural signatures, we identified several features that differ significantly between reversible and structural disulfides, including disulfide bond length, along with the number, amino acid composition, secondary structure and physical-chemical properties of surrounding amino acids. A SVM-based classifier was developed for predicting reversible disulfides. RESULTS: By 10-fold cross-validation, the model achieved accuracy of 0.750, sensitivity of 0.352, specificity of 0.953, MCC of 0.405 and AUC of 0.751 using the RevSS_PDB dataset. The robustness was further validated by using RevSS_RedoxDB as independent testing dataset. This model was applied to proteins with known structures in the PDB database. The results show that one third of the predicted reversible disulfide containing proteins are well-known redox enzymes, while the remaining are non-enzyme proteins. Given that reversible disulfides are frequently reported from functionally important non-enzyme proteins such as transcription factors, the predictions may provide valuable candidates of novel reversible disulfides for further experimental investigation. CONCLUSIONS: This study provides the first comparative analysis between the reversible and the structural disulfides. Distinct features remarkably different between these two groups of disulfides were identified, and a SVM-based classifier for predicting reversible disulfides was developed accordingly. A web server named RevssPred can be accessed freely from: http://biocomputer.bio.cuhk.edu.hk/RevssPred .

The dynamics of DNA methylation fidelity during mouse embryonic stem cell self-renewal and differentiation.

The faithful transmission of DNA methylation patterns through cell divisions is essential for the daughter cells to retain a proper cell identity. To achieve a comprehensive assessment of methylation fidelity, we implemented a genome-scale hairpin bisulfite sequencing approach to generate methylation data for DNA double strands simultaneously. We show here that methylation fidelity increases globally during differentiation of mouse embryonic stem cells (mESCs), and is particularly high in the promoter regions of actively expressed genes and positively correlated with active histone modification marks and binding of transcription factors. The majority of intermediately (40%-60%) methylated CpG dinucleotides are hemi-methylated and have low methylation fidelity, particularly in the differentiating mESCs. While 5-hmC and 5-mC tend to coexist, there is no significant correlation between 5-hmC levels and methylation fidelity. Our findings may shed new light on our understanding of the origins of methylation variations and the mechanisms underlying DNA methylation transmission.