Biology subjects

Vijg, J.

Publications and source records attributed to Vijg, J..

23 records · Page 2Linked to original sources

bioRxiv2019

Single-cell whole-genome sequencing reveals mutational landscapes of DNA mismatch repair deficiency in mouse primary fibroblasts

DNA Mismatch repair (MMR) deficiency is a major cause of hereditary non-polyposis colorectal cancer, and is also associated with increased risk of several other cancers. This is generally ascribed to the role of MMR in avoiding mutations by correcting DNA replication errors. In MMR knockout mice very high frequencies of somatic mutations, up until 100-fold of background, have been reported. However, these results have been obtained using bacterial reporter transgenes, which are not representative for the genome overall, and mutational patterns of MMR deficiency remain largely unknown. To fill this knowledge gap, we performed single-cell whole-genome sequencing of lung fibroblasts of Msh2-/- and wild-type mice. We observed a 4-fold increase of somatic single nucleotide variants (SNVs) in the fibroblasts of Msh2-/- mice compared to those of wild-type mice. The SNV signature of Msh2 deficiency was found to be driven by C>T and T>C transitions. By comparing it to human cancer signatures, we not only confirmed the inferred MMR-deficiency-related etiology of several cancer signatures but also suggested that MMR deficiency is likely the cause of a cancer signature with its etiology previously unknown. We also observed a 7-fold increase of somatic small insertions and deletions (INDELs) in the Msh2-/- mice. An elevated INDEL frequency has also been found in human MMR-related cancers. INDELs and SNVs distributed differently across genomic features in the Msh2-/- and control cells, with evidence of selection pressure and repair preference. These results provide insights into the landscape of somatic mutations in normal somatic cells caused by MMR deficiency.\n\nSignificanceOur results show that MMR deficiency in the mouse is associated with a much lower elevation of somatic mutation rates than previously reported and provides the first MMR whole-genome mutational landscapes in normal somatic cells in vivo.

genomics↗

bioRxiv2019

Single-cell analysis reveals different age-related somatic mutation profiles between stem and differentiated cells in human liver

Accumulating somatic mutations have been implicated in age-related cellular degeneration and death. Because of their random nature and low abundance, somatic mutations are difficult to detect except in single cells or clonal lineages. Here we show that in single hepatocytes from human liver, an organ normally exposed to high levels of genotoxic stress, somatic mutation frequencies are high and increase substantially with age. Significantly lower mutation frequencies were observed in liver stem cells and organoids derived from them. These results could explain the increased age-related incidence of liver disease in humans and stress the importance of stem cells in maintaining genome integrity.

genomics↗

bioRxiv2019

SCCNV: a software tool for identifying copy number variation from single-cell whole-genome sequencing

BackgroundIdentification of de novo mutations from cell populations requires single-cell whole-genome sequencing (SCWGS). Although many experimental protocols of SCWGS have been developed, few computational tools are available for downstream analysis of different types of somatic mutations, including copy number variation (CNV). ResultsWe developed SCCNV, a software tool for detecting CNVs from whole genome-amplified single cells. SCCNV is a read-depth based approach with adjustment for the whole-genome amplification bias. ConclusionsWe demonstrate its performance by analyzing data collected from most of the single-cell amplification methods, including DOP-PCR, MDA, MALBAC and LIANTI. SCCNV is freely available at https://github.com/biosinodx/SCCNV.

bioinformatics↗

bioRxiv2019

Single-cell whole-genome sequencing reveals the functional landscape of somatic mutations in B lymphocytes across the human lifespan

Introductory paragraphThe accumulation of mutations in somatic cells have been implicated as a cause of ageing since the 1950s1,2. Yet, attempts to establish a causal relationship between somatic mutations and ageing have been constrained by the lack of methods to directly identify mutational events in primary human tissues. Here we provide detailed, genome-wide mutation frequencies and spectra of human B lymphocytes from healthy individuals across the entire human lifespan, from newborns to centenarians, using a recently developed, highly accurate single-cell whole-genome sequencing method3. We found that the number of somatic mutations increases from <500 per cell in newborns to >3,000 per cell in centenarians. We discovered mutational hotspot regions, some of which, as expected, located at immunoglobulin genes associated with somatic hypermutation. B cell-specific mutation signatures were observed associated with development, ageing or somatic hypermutation (SHM). The SHM signature strongly correlated with the signature found in human chronic lymphocytic leukemia and malignant B-cell lymphomas4, indicating that even in B cells of healthy individuals the potential cancer-causing events are already present. We also identified multiple mutations in sequence features relevant to cellular function, i.e., transcribed genes and gene regulatory regions. Such mutations increased significantly during ageing, but only at approximately half the rate of the genome average, indicating selection against mutations that impact B cell function. This first full characterization of the landscape of somatic mutations in human B lymphocytes indicates that spontaneous somatic mutations accumulating with age can be deleterious and may contribute to both the increased risk for leukemia and the functional decline of B lymphocytes in the elderly.

genomics↗

bioRxiv2019

Spontaneous retrotranspositions in normal tissues are rare and associated with cell-type-specific differentiation

Activation of retrotransposons and their insertions into new genomic locations, i.e., retrotranspositions (RTs), have been identified in about 50% of tumors. However, the landscape of RTs in different, normal somatic cell types in humans remains largely unknown. Using single-cell whole-genome sequencing we identified 528 RT events, including LINE-1 (L1), and Alu, in 164 single cells and clones of fibroblasts, neurons, B lymphocytes, hepatocytes and liver stem cells, of 29 healthy human subjects aged from 0 to 106 years. The frequency of RTs was found to vary from <1 on average per cell in primary fibroblasts to 7.8 per cell in hepatocytes. Somewhat surprisingly, RT frequency does not increase with age, which is in contrast to other types of spontaneous mutation. RTs were found significantly more likely to insert in or close to target genes of the Polycomb Repressive Complex 2 (PRC2), which represses most of the genes encoding developmental regulators through H3K27me3 histone modification in embryonic stem cells. Indeed, when directly comparing RT frequency between differentiated liver hepatocytes with liver stem cells, the latter were almost devoid of RTs. These results indicate that spontaneous RTs are associated with cellular differentiation and occur, possibly, as a consequence of the transient chromatin transition of differentiation-specific genes from a transcriptionally repressed to activated state during the differentiation process.

genomics↗