Cell-specific inducible gene recombination in postnatal inner ear supporting cells and glia

GÓMEZ-CASATI, ME; MURTIE J; CORFAS G

Phoenix, AZ, USA

Congreso; The Association for Research in Otolaryngology, midwinter meeting; 2008

In spite of the prevalence of progressive hearing and balance disorders, the cellular and molecular mechanisms that contribute to the long-term structural and functional integrity of the cochlea and vestibular organs remain poorly understood. It has been proposed that hair cells are the most critical source of survival signals for adult sensory neurons in the inner ear: most neuronal degeneration in the cochlea is restricted to regions in which the inner hair cells are destroyed. However, recent studies indicates that supporting cells of the organ of Corti and vestibular sensory epithelia also play key roles in maintaining hearing and vestibular function in the adult. Supporting cells of the inner ear have molecular similarities to glial cells. They express several glial markers, like the proteolipid protein (PLP), a protein express in oligodendrocytes and myelinating Scwhann cells. Thus, interactions between neurons and supporting cells may contribute to cell survival in the inner ear by mechanisms similar to those involved in neuron-glia interactions.The aim of our work is to elucidate these interactions by generating mice in which we can externally induce gene deletion or overexpression in supporting cells. We use the system that employs a fusion protein between the Cre recombinase and a mutated ligand-binding domain of the human estrogen receptor (CreERT) under the transcriptional control of the PLP promoter. In these mice, the Cre recombinase will be expressed by all cells in which the promoter is active, but will remain inactive until mice are injected with tamoxifen. Only then will Cre move into the nucleus and produce loxP-mediated recombination of the target gene. To assess the activity of the CreERT fusion protein following treatment with tamoxifen, we use the reporter mice Rosa26, a transgenic line in which the LacZ gene encoding b-galactosidase (b-gal) is expressed only after Cre-mediated excision of a LoxP-flanqued stop cassette. PLP-CreERT mice were crossed with Rosa26 reporter mice. When PLP-CreERT; Rosa26 mice were injected with tamoxifen, specific b-gal activity was detected in supporting cells and Schwann cells of the inner ear. Specifically, in the cochlea, b-gal activity was found in inner phalangeal cells along the entire length. In the vestibular sensory organs, supporting cells that surrounded both type I and II hair cells were positive. Cre activity was virtually nonexistent in uninduced mice.These results shows that the PLP-CreERT mouse line provides a powerful tool to dissect gene function at early and late stages in development of the inner ear. Such information will be important in understanding, and ultimately controlling, neuronal loss in the inner ear and the sensory impairment it produces.