RESUMO
Cell-free extrachromosomal circular DNA (eccDNA) as a distinct topological form from linear DNA has recently gained increasing research interest, with possible clinical applications as a class of biomarkers. In this study, we aimed to explore the relationship between nucleases and eccDNA characteristics in plasma. By using knockout mouse models with deficiencies in deoxyribonuclease 1 (DNASE1) or deoxyribonuclease 1 like 3 (DNASE1L3), we found that cell-free eccDNA in Dnase1l3-/- mice exhibited larger size distributions than that in wild-type mice. Such size alterations were not found in tissue eccDNA of either Dnase1-/- or Dnase1l3-/- mice, suggesting that DNASE1L3 could digest eccDNA extracellularly but did not seem to affect intracellular eccDNA. Using a mouse pregnancy model, we observed that in Dnase1l3-/- mice pregnant with Dnase1l3+/- fetuses, the eccDNA in the maternal plasma was shorter compared with that of Dnase1l3-/- mice carrying Dnase1l3-/- fetuses, highlighting the systemic effects of circulating fetal DNASE1L3 degrading the maternal eccDNA extracellularly. Furthermore, plasma eccDNA in patients with DNASE1L3 mutations also exhibited longer size distributions than that in healthy controls. Taken together, this study provided a hitherto missing link between nuclease activity and the biological manifestations of eccDNA in plasma, paving the way for future biomarker development of this special form of DNA molecules.
Assuntos
DNA , Feto , Animais , DNA Circular/genética , Desoxirribonucleases/genética , Endodesoxirribonucleases/genética , Endodesoxirribonucleases/metabolismo , Feminino , Feto/metabolismo , Humanos , Camundongos , Camundongos Knockout , GravidezRESUMO
We developed genetic-epigenetic tissue mapping (GETMap) to determine the tissue composition of plasma DNA carrying genetic variants not present in the constitutional genome through comparing their methylation profiles with relevant tissues. We validated this approach by showing that, in pregnant women, circulating DNA carrying fetal-specific alleles was entirely placenta-derived. In lung transplant recipients, we showed that, at 72 hr after transplantation, the lung contributed only a median of 17% to the plasma DNA carrying donor-specific alleles, and hematopoietic cells contributed a median of 78%. In hepatocellular cancer patients, the liver was identified as the predominant source of plasma DNA carrying tumor-specific mutations. In a pregnant woman with lymphoma, plasma DNA molecules carrying cancer mutations and fetal-specific alleles were accurately shown to be derived from the lymphocytes and placenta, respectively. Analysis of tissue origin for plasma DNA carrying genetic variants is potentially useful for noninvasive prenatal testing, transplantation monitoring, and cancer screening.
Assuntos
DNA/sangue , Epigenômica/métodos , Neoplasias/genética , Transplante de Órgãos/métodos , Diagnóstico Pré-Natal/métodos , Adulto , Idoso , Biomarcadores Tumorais/genética , Carcinoma Hepatocelular/genética , DNA/genética , Metilação de DNA , DNA de Neoplasias/sangue , DNA de Neoplasias/genética , Epigênese Genética , Feminino , Feto/metabolismo , Variação Genética , Humanos , Neoplasias Hepáticas/genética , Linfoma/genética , Masculino , Pessoa de Meia-Idade , Neoplasias/sangue , Placenta/metabolismo , Gravidez , Análise de Sequência de DNA/métodosRESUMO
The presence of fetal DNA in the plasma of pregnant women has opened up new possibilities for noninvasive prenatal diagnosis. Over the past decades, different types of fetal markers have been developed, initially based on discriminative genetic markers such as male-specific signals or paternally-inherited polymorphisms, and gradually evolved to the detection of fetal-specific transcripts or epigenetic signatures. This development has extended the coverage of the application of cell-free fetal DNA to essentially all pregnancies, regardless of the gender of the fetus or its polymorphic status. In this review, we present an overview of the development of noninvasive prenatal diagnosis through epigenetics. We introduce the basis of how fetal DNA could be detected from a large background of maternal DNA in maternal plasma based on fetal-specific DNA methylation patterns. We evaluate the methodologies involved and discuss the factors that affect the robustness of the detection. We review the progress in adopting fetal epigenetic markers for noninvasive prenatal assessment of fetal chromosomal aneuploidies and pregnancy-associated disorders. We conclude with comments on the future directions regarding the search for new fetal epigenetic markers and the clinical implementation of epigenetic approaches for noninvasive prenatal diagnosis.
