Characterization of a unique cell population marked by transgene expression in the adult cochlea of nestin‐CreER^T2/tdTomato‐reporter mice

Abstract

Hair cells in the adult mammalian cochlea cannot spontaneously regenerate after damage resulting in the permanency of hearing loss. Stem cells have been found to be present in the cochlea of young rodents; however, there has been little evidence for their existence into adulthood. We used nestin-CreERT2/tdTomato-reporter mice to trace the lineage of putative nestin-expressing cells and their progeny in the cochleae of adult mice. Nestin, an intermediate filament found in neural progenitor cells during early development and adulthood, is regarded as a multi-potent and neural stem cell marker. Other investigators have reported its presence in postnatal and young adult rodents; however, there are discrepancies amongst these reports. Using lineage tracing, we documented a robust population of tdTomato-expressing cells and evaluated these cells at a series of adult time points. Upon activation of the nestin promoter, tdTomato was observed just below and medial to the inner hair cell layer. All cells co-localized with the stem cell and cochlear-supporting-cell marker Sox2 as well as the supporting cell and Schwann cell marker Sox10; however, they did not co-localize with the Schwann cell marker Krox20, spiral ganglion marker NF200, or GFAP-expressing supporting cell marker. The cellular identity of this unique population of tdTomato-expressing cells in the adult cochlea of nestin-CreERT2/tdTomato mice remains unclear however these cells may represent a type of supporting cell on the neural aspect of the inner hair cell layer.

Evaluation of Nestin Expression in the Developing and Adult Mouse Inner Ear

“…For all samples, cochlear tissue was harvested within 1 week after tamoxifen injection. Previous analysis confirmed appropriate morphological appearance and expression of tdTomato in nestin-CreER T2 / tdTomato-reporter mice, with no tdTomato observed within the cochlea in the absence of tamoxifen [26].…”

“…Cochlear expression of nestin-GFP in the mature cochlea By P30, the expression pattern of GFP remains fairly stable, with GFP observed in Deiters' cells and in a cell population just under and medial to the inner hair cells, in a similar cell population where we identified nestin-tdTomato in a previous study [26]. We were unable to determine if this cell population represents supporting cells at the medial aspect of the organ of Corti or peripherally located cells of the spiral ganglion region, hereafter referred to as the osseous spiral lamina [26].…”

“…We were unable to determine if this cell population represents supporting cells at the medial aspect of the organ of Corti or peripherally located cells of the spiral ganglion region, hereafter referred to as the osseous spiral lamina [26]. At 6 weeks of age, GFP was observed in only these two regions.…”

“…The promoter of pregnant dams was activated with tamoxifen (250 mg/kg/ip body weight, 30 mg/mL in 10% EtOH mixed with sunflower oil) [15,26,33] at E11.5, E13.5, E14.5, E15.5, E16.5, or E19.5. A single dose of tamoxifen was administered to each pregnant dam.…”

“…Several reports describe the expression of nestin in the murine cochlea [22][23][24][25][26]. These studies provide insight into its distribution in neonatal, postnatal and adult mice; however, the dynamic expression pattern of nestin in the developing cochlea has not been systematically characterized.…”