Figure 2.

Genetic lineage tracing by Cre-loxP recombination. (A) Diagram of constitutive genetic lineage tracing strategy. Cre is under the control of a tissue-specific promoter and reporter is on Rosa26 locus where there is STOP sequence flanked by loxP before the reporter. In Cre⁺ cells, Cre-loxP-mediated recombination removes the STOP sequence and leads to labeling (e.g., GFP) of Cre⁺ cells and all their descendants (with or without Cre expression). (B) Diagram of inducible genetic lineage tracing strategy. CreER, a fusion protein of Cre and estrogen receptor (ER), is located in the cytoplasm. In the presence of tamoxifen, CreER is translocated to the nucleus, where CreER-loxP recombination removes the STOP sequence to label the CreER⁺ cells and their descendants.