What is CreERT2?

By fusing the ligand binding region (LBD) of the human estrogen receptor (ER) with Cre recombinase, a fusion protein (Cre-ER) localized in the cytoplasm can be generated. Only upon estrogen induction, the fused Cre protein can dissociate from the anchor protein HSP90 via conformational changes and enter the nucleus, where the Cre protein recognizes the loxP site and undergoes recombination. In this way, by controlling the injection time of estrogen, the time-specific regulation of gene recombination can be achieved.

In order to avoid the interference by endogenous estrogen, a point mutation (G521R) can be generated in the ligand binding region, thus allowing Cre-ER to only respond to the induction by exogenous synthetic estrogens (e.g., Tamoxifen, 4-OHT). Such fusion protein is named as Cre-ERT. Another fusion protein carrying LBD mutation, the well-known Cre-ERT2, was shown to be much more sensitive to 4-OHT than Cre-ERT. It carries three point mutations in the human ER LBD: C400V/M453A/L544A.

Figure 6. Schematic diagram of Tamoxifen-induced activation of Cre. (The picture is from Inducible CreMice. Methods in Molecular Biology 530:343-63 February 2009).