Fate-mapping analysis of cochlear cells expressing Atoh1 mRNA via a new Atoh1(3*HA-P2A-Cre) knockin mouse strain

Background Atoh1 is recognized to be essential for cochlear hair cell (HC) development. However, Atoh1 temporal and spatial expression patterns remain widely debated. Here, we aimed to obtain evidence to resolve the controversies regarding Atoh1 expression by generating a new knockin mouse strain: Atoh1(3*HA-P2A-Cre). Results Fate-mapping analysis of Atoh1(3*HA-P2A-Cre/+); Rosa26-CAG-LSL-tdTomato (Ai9)/+ mice enabled us to concurrently characterize the temporal expression of Atoh1 protein (through HA-tag immunostaining) and visualize the cells expressing Atoh1 mRNA (as tdTomato+ cells). Our findings show that whereas Atoh1 mRNA expression is rapidly turned on in early cochlear progenitors, Atoh1 protein is only detected in differentiating HCs or progenitors just committed to the HC fate. Cre activity is also stronger in Atoh1(3*HA-P2A-Cre/+) than in previous mouse models, because almost all cochlear HCs and nearby supporting cells here are tdTomato+. Furthermore, tdTomato, but not HA, is expressed in middle and apical spiral ganglion neurons. Conclusion Collectively, our findings indicate that Atoh1(3*HA-P2A-Cre) can serve as a powerful genetic model in the developmental biology field.