F-box protein 2 (encoded by Fbxo2) is a ubiquitin ligase involved in regulation of protein turnover via the Skp1/Cullin1/F-Box/Rbx1 (SCF) ubiquitin ligase complex. Fbxo2 is highly expressed in neural tissue and in the mechanosensory cells of the inner ear. These Fbxo2CreERT2 knock-in/knock-out (KI/KO) mice express a CreER fusion protein driven by the F-box protein 2 (Fbxo2) endogenous promoter, while abolishing endogenous Fbxo2 expression. Homozygous mice are viable and fertile. Even though previous Fbxo2 null mice have been shown to have cochlear degeneration, these Fbxo2CreERT2 KI/KO mice do not display age-related cochlear degeneration or hearing loss. Restricted to the cytoplasm, Cre-ERT can only gain access to the nuclear compartment after exposure to tamoxifen. When Fbxo2CreERT2 mice are bred with mice containing loxP-flanked sequences, tamoxifen-inducible Cre-mediated recombination will result in deletion of the floxed sequences in the cre-expressing cells of the offspring. The donating laboratory confirmed Cre-recombinase activity in the developing and mature inner ear by crossing these mice to an Rosa26loxp-stop-loxp-tdTomato, also known as Ai9, mouse line (Stock No. <a href="https://www.jax.org/strain/007909">007909</a>). After tamoxifen administration, resulting progeny demonstrated tdTomato expression beginning at embryonic day 15.5 (E15.5) in the organ of corti, sensory domains of the crista and maculae as well as in some cochlear duct non-sensory cells. tdTomato expression was also noted in cerebellum and sensory olfactory epithelium and the mesenchymal core of the pinna at E15.5. Significant fluorescent expression was noted in many cells in the cochlear duct and vestibular organs in both neonatal and adult mice post tamoxifen induction. These Fbxo2CreERT2 KI/KO mice may be useful for studying inner ear sensory cell development and differentiation.

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Fbxo2CreERT2 knock-in/knock-out mice express a CreER fusion protein driven by the F-box protein 2 (Fbxo2) endogenous promoter, while abolishing endogenous Fbxo2 expression. When these mice are bred with mice containing a loxP-flanked sequence of interest, tamoxifen-inducible, Cre-mediated recombination will result in deletion of the floxed sequences in the Fbxo2-expressing cells of the offspring. These mice may be useful when studying inner ear sensory epithelial cells.

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