Abstract
Stem cell dynamics in vivo are often being studied by lineage tracing methods. Our laboratory has previously developed a retrospective method for reconstructing cell lineage trees from somatic mutations accumulated in microsatellites. This method was applied here to explore different aspects of stem cell dynamics in the mouse colon without the use of stem cell markers. We first demonstrated the reliability of our method for the study of stem cells by confirming previously established facts, and then we addressed open questions. Our findings confirmed that colon crypts are monoclonal and that, throughout adulthood, the process of monoclonal conversion plays a major role in the maintenance of crypts. The absence of immortal strand mechanism in crypts stem cells was validated by the age-dependent accumulation of microsatellite mutations. In addition, we confirmed the positive correlation between physical and lineage proximity of crypts, by showing that the colon is separated into small domains that share a common ancestor. We gained new data demonstrating that colon epithelium is clustered separately from hematopoietic and other cell types, indicating that the colon is constituted of few progenitors and ruling out significant renewal of colonic epithelium from hematopoietic cells during adulthood. Overall, our study demonstrates the reliability of cell lineage reconstruction for the study of stem cell dynamics, and it further addresses open questions in colon stem cells. In addition, this method can be applied to study stem cell dynamics in other systems.
Highlights
Mammalian stem cells and tissue dynamics in vivo are presently studied by lineage tracing methods [1,2], which are dependent on the presence of specific stem cell markers [2]
We focused on the intestinal epithelium, since its stem cells were intensively studied by various tracing methods that clarified many aspects of their dynamics [2,14,15,16,17,18,19,20,21]
We first showed the reliability of our method by confirming three previously established facts: the existence of ‘‘monoclonal conversion,’’ the absence of an immortal strand mechanism in colon stem cells, and the separation of the colon into small domains each with a common ancestor
Summary
Mammalian stem cells and tissue dynamics in vivo are presently studied by lineage tracing methods [1,2], which are dependent on the presence of specific stem cell markers [2]. Our laboratory developed a method that utilizes somatic microsatellite (MS) mutations for reconstructing cell lineage trees [4,5,6,7] This retrospective method, which was applied by others [8,9,10,11], is based on the notion that somatic mutations accumulated during normal cell divisions endow each cell of the body with a genomic signature that, with very high probability, is unique [4]. The MS mutation rate of these mice is much higher than that of wild type, increasing the precision of the cell lineage analysis These mice exhibit normal morphology, but are infertile and develop cancer spontaneously [13]. It was employed to estimate the number of cell divisions since the zygote, defined as cell depth [6]
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