Discovering New Progenitor Cell Populations through Lineage Tracing and In Vivo Imaging

Abstract

Identification of progenitor cells that generate differentiated cell types during development, regeneration, and disease states is central to understanding the mechanisms governing such transitions. For more than a century, different lineage-tracing strategies have been developed, which helped disentangle the complex relationship between progenitor cells and their progenies. In this review, we discuss how lineage-tracing analyses have evolved alongside technological advances, and how this approach has contributed to the identification of progenitor cells in different contexts of cell differentiation. We also highlight a few examples in which lineage-tracing experiments have been instrumental for resolving long-standing debates and for identifying unexpected cellular origins. This discussion emphasizes how this century-old quest to delineate cellular lineage relationships is still active, and new discoveries are being made with the development of newer methodologies.

Cellular Origins of the Lymphatic Endothelium: Implications for Cancer Lymphangiogenesis

“…As a whole, work in the recent years has begun to shed light on the heterogeneous origins of organ-specific lymphatics. Yet, it is important to keep in mind that while lineage tracing approaches have been instrumental for identifying novel progenitor populations and establishing lineage relationships within cell progeny/populations (Das and Yaniv, 2020), this technique harbors also intrinsic technical limitations. Unspecific or leaky drivers might erroneously label undesired populations, whereas the absence of specific labeling in certain cells can derive from an inefficient driver, all of these leading to potential misinterpretation of the results (reviewed in Semo et al, 2016).…”

Mechanisms and cell lineages in lymphatic vascular development

“…The Cre enzyme from the P1 bacteriophage is a site-specific recombinase that excises DNA segments flanked by loxP sites [ 98 ]. For genetic lineage tracing, Cre is expressed under the control of a promoter that drives cell-type specific gene expression, either from a transgene or when knocked directly into the endogenous locus.…”

The cellular origins of cancer with particular reference to the gastrointestinal tract

“…Heritable genetic lineage tracing is well established in experimental animals [18][19][20] but such techniques are not available for human studies. However, the mitochondrial genome is highly prone to non-pathogenic (passenger) mutations that can be used as clonal markers in human tissue.…”

“…The discovery of site-specific recombination systems has revolutionized lineage tracing in vertebrates, 18,20 one of the most common systems being the Cre-lox system, allowing DNA modifications to be targeted to a specific cell type. LoxP sites are short (34 bp) DNA stretches that under the catalysing influence of Cre recombinase undergo DNA cleavage and reciprocal strand exchange with another loxP site.…”

“…Problems with site-specific recombination are often due to the specificity of the drivers used for Cre expression, for example promiscuity of Cre expression leading to unwanted (off-target) labelling, and these are discussed elsewhere. 18,20 F I G U R E 5 A, For lineage labelling, a stable transcriptional driver such as the cytomegalovirus (CMV) or ROSA26 promoter is engineered upstream of the reporter gene, and a loxP flanked stop signal (loxP-STOP-loxP [LSL]) is placed between these two sequences. In the presence of Cre, recombination of the loxP sites removes the LSL sequence to allow expression of the reporter gene.…”