Inducible and tissue‐specific cell labeling in Cre‐ER ( T2 ) transgenic Xenopus lines

Investigating cell lineage requires genetic tools that label cells in a temporal and tissue‐specific manner. The bacteriophage‐derived Cre‐ER ( T2 ) /loxP system has been developed as a genetic tool for lineage tracing in many organisms. We recently reported a stable transgenic Xenopus line with a Cre‐ER ( T2 ) /loxP system driven by the mouse Prrx1 (mPrrx1) enhancer to trace limb fibroblasts during the regeneration process (Prrx1:CreER line). Here we describe the detailed technological development and characterization of such line. Transgenic lines carrying a CAG promoter‐driven Cre‐ER ( T2 ) /loxP system showed conditional labeling of muscle, epidermal, and interstitial cells in both the tadpole tail and the froglet leg upon 4‐hydroxytamoxifen (4OHT) treatment. We further improved the labeling efficiency in the Prrx1:CreER lines from 12.0% to 32.9% using the optimized 4OHT treatment regime. Careful histological examination showed that Prrx1:CreER lines also sparsely labeled cells in the brain, spinal cord, head dermis, and fibroblasts in the tail. This work provides the first demonstration of conditional, tissue‐specific cell labeling with the Cre‐ER ( T2 ) /loxP system in stable transgenic Xenopus lines.