Engineering a Membrane‐Anchored CreER Recombinase With Reduced Basal Activity for In Vitro Recombination

The CreER-loxP system is widely utilized for genetic cell lineage tracing and conditional gene function analysis. However, issues have arisen concerning the unintended labeling of nontarget cell populations, which complicate experimental data analysis and interpretation. In this study, we constructed an engineered CreER-loxP system in which a membrane‑localization motif was fused to the C‑terminus of Cre, thereby anchoring the fusion protein to the cell membrane and minimizing its spontaneous leakage into the nucleus. This membrane‑tethered CreER-loxP (mCreER-loxP) system substantially reduced nonspecific labeling in the absence of tamoxifen. Upon tamoxifen induction, the membrane‑localized Cre dissociated from the membrane and translocated into the nucleus, maintaining comparable recombination efficiency with the conventional CreER-loxP system. Notably, the membrane‑tethering design demonstrates enhanced performance under conditions of high expression levels and extended duration in vitro, even within the more stringent ERCreER-loxP labeling framework. Furthermore, mCreER exhibited reduced cytotoxicity relative to standard CreER. Collectively, these results indicate that the mCreER-loxP system provides improved temporal and spatial precision for applications in cell lineage tracing and genetic engineering.