Determining lineage relationships in kidney development and disease.

The lineage relationships of cells provide information about the origins of component cell types during development and repair as well as the source of aberrant cells during disease. Genetic approaches to lineage tracing applied in the mouse have revealed much about how the mammalian kidney forms, including the identification of key progenitors for the nephrons and stromal compartments. Inducible Cre systems have also facilitated lineage tracing studies in the postnatal animal that illustrate the changes in cellular fate that can occur during kidney injury. With the advent of single-cell transcriptional profiling and trajectory analyses, predictions of cellular relationships across development are now being made in model systems, such as the mouse, as well as in human fetal kidney. Importantly, these approaches provide predictions of lineage relationships rather than definitive evidence. Although genetic approaches to the study of lineage have not previously been possible in a human setting, the application of CRISPR-Cas9 gene editing of pluripotent stem cells is beginning to teach us about human lineage relationships.