Single-Cell Lineage Tracing and Clonal State-Fate Analysis

Lineage tracing has significantly advanced our comprehension in many areas of biology, such as development or immunity, by precisely measuring cellular processes like migration, division, or differentiation across labeled cells and their progeny. Traditional recombinase-based prospective lineage tracing is limited by the need for a priori cell type information and is constrained in the numbers of clones it can simultaneously track. In this sense, clonal lineage tracing with integrated random barcodes offers a robust alternative, enabling researchers to label and track a vast array of cells and their progeny over time. Moreover, clonal lineage tracing can be combined with single-cell omics technologies to study cell states and their maintenance over time. Key steps in these protocols include stable barcode integration, cell division to expand clones, and simultaneous capture of cellular properties with barcode information. Here, we comment on those steps and summarize important parameters to take into account during the design of single-cell lineage tracing experiments. Also, we present the main features for various available lentiviral libraries of expressed barcodes than can be captured alongside the transcriptome of individual cells. We cover other crucial aspects of experimental design, such as the optimization of cellular sampling, library diversity, and the minimization of clonal dropouts. Regarding sequencing data analysis, we provide some tips based on our experience, as well as available computational tools for the assignment of clonal identities and the identification of fate determinants. We finally discuss limitations of current methodologies and use an example step-by-step protocol to illustrate key points during the process. In sum, we provide a roadmap for considering and implementing single-cell lineage tracing studies to comprehensively explore fate determinants and their mechanisms.