Generation and characterization of a complete null estrogen receptor alpha mouse using Cre/LoxP technology

Conventional estrogen receptor alpha knockout (neo-ER alpha KO, neo-ER alpha(-/-)) mice contain a truncated and chimeric ER alpha fusion protein that retains 35% estrogen-dependent transactivation activity, and therefore the in vivo ER alpha function is difficult to study thoroughly. Furthermore, these neo-ER alpha(-/-) mice cannot be used for tissue and temporal specific ER alpha deletion. Therefore, there is a clear need to establish a floxed ER alpha mouse line that can knockout ER alpha specifically and completely in each selected cell type. Here we generated floxed ER alpha mice using a self-excising ACN (tACE-Cre/Neo) cassette. Mating the floxed ER alpha mice with ACTB-Cre mice produces a deletion of the floxed allele disrupting the reading frame of the ER alpha transcript so that no ER alpha protein is detected in the ACTB-Cre/ER alpha(-/-) mice. Expression of ER alpha target genes, such as G-6-PD and lactoferrin, is diminished by over 90% in the ACTB-Cre/ER alpha(-/-) uterus, but not in the neo-ER alpha(-/-) uterus. Furthermore, we also validated that ACTB-Cre/ER alpha(-/-) females have a hypoplastic internal genital tract, polycystic ovaries with hemorrhagic follicles, infertility, and higher body weight. Together, our data clearly demonstrate that the newly established floxed ER alpha mouse is a reliable mouse model for future studies of ER alpha roles in vivo in the selective estrogen target tissues. The complete knockout of ER alpha in the ACTB-Cre/ER alpha(-/-) mice will also provide an improved mouse model to study the role of ER alpha in vivo.