Clonal expansion dictates the efficacy of mitochondrial lineage tracing in single cells

Abstract

Background: Mitochondrial DNA (mtDNA) variants hold promise as endogenous barcodes for tracking human cell lineages, but their efficacy as reliable lineage markers are hindered by the complex dynamics of mtDNA in somatic tissues. Results: Here, we use computational modeling and single-cell genomics to thoroughly interrogate the origin and clonal dynamics of mtDNA variants across various biological settings. Our findings reveal that the majority of mtDNA variants which are specifically present in a cell subpopulation, termed subpopulation-specific variants, are pre-existing heteroplasmies in the first cell instead of de novo somatic mutations during divisions. Moreover, subpopulation-specific variants demonstrate limited discriminatory power among different genuine lineages under weak clonal expansion; however, certain subpopulation-specific variants with consistently high frequencies among a subpopulation are capable of faithfully labeling cell lineages in scenarios of stringent clonal expansion, such as strongly expanded T cell populations in diseased conditions and clonal hematopoiesis in aged individuals. Inspired by our simulations, we introduce a lineage informative score, facilitating the identification of reliable mitochondrial lineage tracing markers across different modalities of single-cell genomic data. Conclusions: Combining computational modeling and single-cell sequencing, our study reveals that the performance of mitochondrial lineage tracing is highly dependent on the extent of clonal expansion, which thus should be considered when applying mitochondrial lineage tracing.