Identification and Characterization of Extrachromosomal Circular DNA in Human Placentas With Fetal Growth Restriction

Molecular characterization and functional roles of circulating cell-free extrachromosomal circular DNA

Circular DNA segments isolated from chromosomes are known as extrachromosomal circular DNA (eccDNA). Its distinct structure and characteristics, along with the variations observed in different disease states, makes it a promising biomarker. Recent studies have revealed the presence of eccDNAs in body fluids, indicating their involvement in various biological functions. This finding opens up avenues for utilizing eccDNAs as convenient and real-time biomarkers for disease diagnosis, treatment monitoring, and prognosis assessment through noninvasive analysis of body fluids. In this comprehensive review, we focused on elucidating the size profiles, potential mechanisms of formation and clearance, detection methods, and potential clinical applications of eccDNAs. We aimed to provide a valuable reference resource for future research in this field.

Innovative insights into extrachromosomal circular DNAs in gynecologic tumors and reproduction

Originating but free from chromosomal DNA, extrachromosomal circular DNAs (eccDNAs) are organized in circular form and have long been found in unicellular and multicellular eukaryotes. Their biogenesis and function are poorly understood as they are characterized by sequence homology with linear DNA, for which few detection methods are available. Recent advances in high-throughput sequencing technologies have revealed that eccDNAs play crucial roles in tumor formation, evolution, and drug resistance as well as aging, genomic diversity, and other biological processes, bringing it back to the research hotspot. Several mechanisms of eccDNA formation have been proposed, including the breakage-fusion-bridge (BFB) and translocation-deletion-amplification models. Gynecologic tumors and disorders of embryonic and fetal development are major threats to human reproductive health. The roles of eccDNAs in these pathological processes have been partially elucidated since the first discovery of eccDNA in pig sperm and the double minutes in ovarian cancer ascites. The present review summarized the research history, biogenesis, and currently available detection and analytical methods for eccDNAs and clarified their functions in gynecologic tumors and reproduction. We also proposed the application of eccDNAs as drug targets and liquid biopsy markers for prenatal diagnosis and the early detection, prognosis, and treatment of gynecologic tumors. This review lays theoretical foundations for future investigations into the complex regulatory networks of eccDNAs in vital physiological and pathological processes.

Identification and characterization of extrachromosomal circular DNA in age-related osteoporosis

Extrachromosomal circular DNA (eccDNA) was once thought to mainly exist in tumour cells, although it was later shown to be ubiquitous in healthy tissues as well. However, the characteristics and properties of eccDNA in healthy tissue or non-cancer tissue are not well understood. This study first analyses the properties, possible formation mechanisms and potential functions of eccDNA in osteoporotic or normal bone tissue. We used circle-seq to demonstrate the expression spectrum of the eccDNA in the bone tissue. A bioinformatics analysis was performed for the differentially expressed eccDNA, and it enriched the Hippo signalling pathway, PI3K-Akt signalling pathway, Ras signal-ling pathway and other signalling pathways that are closely related to osteoporosis (OP). Then, we used real-time polymerase chain reaction and Sanger sequencing to assess human bone marrow mesenchymal stem cells and obtained the base sequence of the eccDNA cyclization site. Overall, eccDNAs in bone tissue are common and may play a significant role in pathways connected to age-related osteoporosis progression.

Methods, bioinformatics tools and databases in ecDNA research: An overview

Extrachromosomal DNA (ecDNA), derived from chromosomes, is a cancer-specific circular DNA molecule. EcDNA drives tumor initiation and progression, which is associated with poor clinical outcomes and drug resistance in a wide range of cancers. Although ecDNA was first discovered in 1965, tremendous technological revolutions in recent years have provided crucial new insights into its key biological functions and regulatory mechanisms. Here, we provide a thorough overview of the methods, bioinformatics tools, and database resources used in ecDNA research, mainly focusing on their performance, strengths, and limitations. This study can provide important reference for selecting the most appropriate method in ecDNA research. Furthermore, we offer suggestions for the current bioinformatics analysis of ecDNA and provide an outlook to the future research.

Genome-Wide Extrachromosomal Circular DNA Profiling of Paired Hepatocellular Carcinoma and Adjacent Liver Tissues

Hepatocellular carcinoma (HCC) develops through multiple mechanisms. While recent studies have shown the presence of extrachromosomal circular DNA (eccDNA) in most cancer types, the eccDNA expression pattern and its association with HCC remain obscure. We aimed to investigate this problem. The genome-wide eccDNA profiles of eight paired HCC and adjacent non-tumor tissue samples were comprehensively elucidated based on Circle-seq, and they were further cross-analyzed with the RNA sequencing data to determine the association between eccDNA expression and transcriptome dysregulation. A total of 60,423 unique eccDNA types were identified. Most of the detected eccDNAs were smaller than 1 kb, with a length up to 182,363 bp and a mean sizes of 674 bp (non-tumor) and 813 bp (tumor), showing a greater association with gene-rich rather than with gene-poor regions. Although there was no statistical difference in length and chromosome distribution, the eccDNA patterns between HCC and adjacent non-tumor tissues showed significant differences at both the chromosomal and single gene levels. Five of the eight HCC tissues showed significantly higher amounts of chromosome 22-derived eccDNA expression compared to the non-tumor tissue. Furthermore, two genes, SLC16A3 and BAIAP2L2, with a higher transcription level in tumor tissues, were related to eccDNAs exclusively detected in three HCC samples and were negatively associated with survival rates in HCC cohorts from public databases. These results indicate the existence and massive heterogeneity of eccDNAs in HCC and adjacent liver tissues, and suggest their potential association with dysregulated gene expression.

Integrative profiling of extrachromosomal circular DNA in placenta and maternal plasma provides insights into the biology of fetal growth restriction and reveals potential biomarkers

Introduction: Fetal growth restriction (FGR) is a placenta-mediated pregnancy complication that predisposes fetuses to perinatal complications. Maternal plasma cell-free DNA harbors DNA originating from placental trophoblasts, which is promising for the prenatal diagnosis and prediction of pregnancy complications. Extrachromosomal circular DNA (eccDNA) is emerging as an ideal biomarker and target for several diseases. Methods: We utilized eccDNA sequencing and bioinformatic pipeline to investigate the characteristics and associations of eccDNA in placenta and maternal plasma, the role of placental eccDNA in the pathogenesis of FGR, and potential plasma eccDNA biomarkers of FGR. Results: Using our bioinformatics pipelines, we identified multi-chromosomal-fragment and single-fragment eccDNA in placenta, but almost exclusively single-fragment eccDNA in maternal plasma. Relative to that in plasma, eccDNA in placenta was larger and substantially more abundant in exons, untranslated regions, promoters, repetitive elements [short interspersed nuclear elements (SINEs)/Alu, SINEs/mammalian-wide interspersed repeats, long terminal repeats/endogenous retrovirus-like elements, and single recognition particle RNA], and transcription factor binding motifs. Placental multi-chromosomal-fragment eccDNA was enriched in confident enhancer regions predicted to pertain to genes in apoptosis, energy, cell growth, and autophagy pathways. Placental eccDNA-associated genes whose abundance differed between the FGR and control groups were associated with immunity-related gene ontology (GO) terms. The combined analysis of plasma and placental eccDNA-associated genes in the FGR and control groups led to the identification of potential biomarkers that were assigned to the GO terms of the epigenetic regulation of gene expression and nutrient-related processes, respectively. Conclusion: Together, our results highlight links between placenta functions and multi-chromosomal-fragment and single-fragment eccDNA. The integrative analysis of placental and plasma eccDNA confirmed the potential of these molecules as disease-specific biomarkers of FGR.

YTHDC1 maintains trophoblasts function by promoting degradation of m6A-modified circMPP1

N6-methyladenosine (m6A) is the most abundant mRNA internal modification in eukaryotic mRNAs. This study focuses on the effect of circMPP1 on placental villi function and the molecular mechanism. First, differentially expressed circular RNAs (circRNAs) in placenta tissues of large-for-gestational-age(LGA) neonates were screened by m6A-circRNA Epitranscriptomic Microarray and bioinformatics analyses. The abnormal expression of circMPP1 in placental tissues and cell lines was validated by RT-qPCR. In-vitro and in-vivo functional experiments were performed to evaluate the role of circMPP1 in placental impairment and fetal dysplasia. The interacting proteins of circMPP1 were identified and validated using RNA pull-down, RNA immunoprecipitation, fluorescence in situ hybridization, and immunofluorescence experiments. Protein interactions and expression levels were detected by Co-immunoprecipitation and western blot analysis. The m6A modification in circMPP1 was verified by methylated RNA immunoprecipitation assay. Bioinformatics analyses showed that circMPP1 was highly expressed in tissues with disordered placental function. In-vitro and in-vivo functional experiments showed that circMPP1 inhibited the function of placental villi. Further mechanism analyses showed that circMPP1 activated the NF-kappa B and MAPK3 signaling pathways. In addition, the m6A "reader" protein YTHDC1 was found to reduce circMPP1 expression via m6A modification. In conclusion, this study demonstrates that YTHDC1 maintains trophoblasts function by promoting degradation of m6A-mediated circMPP1.

Integrated analysis of mRNA and extrachromosomal circular DNA profiles to identify the potential mRNA biomarkers in breast cancer

Extrachromosomal circular DNAs (eccDNAs) have been proved an inseparable relationship with cancer, based on the biological mechanisms of its biogenesis and impact on tumorigenesis, but still lacked of methods to analyze its function on the pathogenesis and progression of breast cancer (BC). The mRNA and eccDNA from BC cell samples (MDA-MB-453 and MCF-12A) were extracted with the removal of rRNA and linear DNA, respectively. High-throughput sequencing and bioinformatics analysis were performed to explore their expression level and molecular characterization of eccDNA. A total number of 161,062 eccDNA ranging from 33 bp to 54229 bp were detected with a median size of 1143 bp, distributed on all chromosomes and enriched on chromosome 20 the most. EccDNAs located in exons, upstream and downstream 2 kb regions were significantly increased compared with background. Analysis of eccDNA-related differentially expressed genes (eccDEGs) showed that FAT2 properly separated the two cells. CTNNB1, CACNA2D2 and CACNA1D were the hub genes with higher degrees in critical modules. All these four genes were significantly differentially expressed between breast invasive carcinoma (BRCA) tissues and normal ones. FAT2 and CTNNB1 correlated with significantly different overall survival (OS) when differentially expressed. The four genes showed a strong correlation with each other significantly and changed between tumor and normal samples. The results showed the potential of FAT2, CTNNB1, CACNA2D2 and CACNA1D as biomarkers with analysis of both DEGs and eccDEGs, which might assist in clinical medical treatment.

EccBase: A high-quality database for exploration and characterization of extrachromosomal circular DNAs in cancer

Extrachromosomal circular DNAs (eccDNAs) are widely observed in eukaryotes. Previous studies have demonstrated that eccDNAs are essential to cancer progression, and found that they can not only express in normal cells to regulate RNA, but also function differently in different tissues. It is of major interest to conduct computational or experiments assay to elucidate the mechanisms of eccDNA function, uncover key eccDNAs associated with diseases, and even develop related algorithms for liquid biopsy. Naturally, a comprehensive eccDNAs data resource is urgently needed to provide annotation and analysis more in-depth research. In this study, we constructed the eccBase (http://www.eccbase.net) in literature curation and database retrieval, which was the first database mainly collecting eccDNAs from Homo sapiens (n = 754,391) and Mus musculus (n = 481,381). Homo sapiens eccDNAs were taken from 50 kinds of cancer tissue and/or cell line, and 5 kinds of healthy tissues. The Mus musculus eccDNAs were sourced from 13 kinds of healthy tissue and/or cell line. We thoroughly annotated all eccDNA molecules in terms of basic information, genomic composition, regulatory elements, epigenetic modifications, and raw data. EccBase provided users with the ability to browse, search, download for targets of interest, as well as similarity alignment by the integrated BLAST. Further, comparative analysis suggested the cancer eccDNA is composed of nucleosomes and is prominently derived from the gene-dense regions. We also initially revealed that eccDNAs are strongly tissue-specific. In short, we have started a robust database for eccDNA resource utilization, which may facilitate studying the role of eccDNA in cancer development and therapy, cell function maintenance, and tissue differentiation.

Whole-genome sequencing of extrachromosomal circular DNA of cerebrospinal fluid of medulloblastoma

BACKGROUND

Medulloblastoma (MB) is a malignant tumor associated with a poor prognosis in part due to a lack of effective detection methods. Extrachromosomal circular DNA (eccDNA) has been associated with multiple tumors. Nonetheless, little is currently known on eccDNA in MB.

METHODS

Genomic features of eccDNAs were identified in MB tissues and matched cerebrospinal fluid (CSF) and compared with corresponding normal samples using Circle map. The nucleotides on both sides of the eccDNAs' breakpoint were analyzed to understand the mechanisms of eccDNA formation. Bioinformatics analysis combined with the Gene Expression Omnibus (GEO) database identified features of eccDNA-related genes in MB. Lasso Cox regression model, univariate and multivariate Cox regression analysis, time-dependent ROC, and Kaplan-Meier curve were used to assess the potential diagnostic and prognostic value of the hub genes.

RESULTS

EccDNA was profiled in matched tumor and CSF samples from MB patients, and control, eccDNA-related genes enriched in MB were identified. The distribution of eccDNAs in the genome was closely related to gene density and the mechanism of eccDNA formation was evaluated. EccDNAs in CSF exhibited similar distribution with matched MB tissues but were differentially expressed between tumor and normal. Ten hub genes prominent in both the eccDNA dataset and the GEO database were selected to classify MB patients to either high- or low-risk groups, and a prognostic nomogram was thus established.

CONCLUSIONS

This study provides preliminary evidence of the characteristics and formation mechanism of eccDNAs in MB and CSF. Importantly, eccDNA-associated hub genes in CSF could be used as diagnostic and prognostic biomarkers for MB.

Extrachromosomal circular DNA: Current status and future prospects

Extrachromosomal circular DNA (eccDNA) is a double-stranded DNA molecule found in various organisms, including humans. In the past few decades, the research on eccDNA has mainly focused on cancers and their associated diseases. Advancements in modern omics technologies have reinvigorated research on eccDNA and shed light on the role of these molecules in a range of diseases and normal cell phenotypes. In this review, we first summarize the formation of eccDNA and its modes of action in eukaryotic cells. We then outline eccDNA as a disease biomarker and reveal its regulatory mechanism. We finally discuss the future prospects of eccDNA, including basic research and clinical application. Thus, with the deepening of understanding and exploration of eccDNAs, they hold great promise in future biomedical research and clinical translational application.

Extrachromosomal circular DNA: biogenesis, structure, functions and diseases

Extrachromosomal circular DNA (eccDNA), ranging in size from tens to millions of base pairs, is independent of conventional chromosomes. Recently, eccDNAs have been considered an unanticipated major source of somatic rearrangements, contributing to genomic remodeling through chimeric circularization and reintegration of circular DNA into the linear genome. In addition, the origin of eccDNA is considered to be associated with essential chromatin-related events, including the formation of super-enhancers and DNA repair machineries. Moreover, our understanding of the properties and functions of eccDNA has continuously and greatly expanded. Emerging investigations demonstrate that eccDNAs serve as multifunctional molecules in various organisms during diversified biological processes, such as epigenetic remodeling, telomere trimming, and the regulation of canonical signaling pathways. Importantly, its special distribution potentiates eccDNA as a measurable biomarker in many diseases, especially cancers. The loss of eccDNA homeostasis facilitates tumor initiation, malignant progression, and heterogeneous evolution in many cancers. An in-depth understanding of eccDNA provides novel insights for precision cancer treatment. In this review, we summarized the discovery history of eccDNA, discussed the biogenesis, characteristics, and functions of eccDNA. Moreover, we emphasized the role of eccDNA during tumor pathogenesis and malignant evolution. Therapeutically, we summarized potential clinical applications that target aberrant eccDNA in multiple diseases.