The onset of hearing triggers nuclear translocation in inner hair cells

Nuclear position is precisely orchestrated during cell division, migration, and maturation of cells and tissues. Here we report a previously unrecognized, programmed movement of the nucleus in rat cochlear inner hair cells. This cell-type specific nuclear movement among hair cells of the inner ear offers a new glimpse into the cellular mechanisms involved in the functional maturation of inner hair cells. In early post-natal days, the nucleus sits at the very basal pole of the hair cell, far from the apically located mechano-transducing stereocilia, but close to where synapses with primary afferent and efferent neurons are forming. By maturity, the nucleus moves to occupy a new position half-way along the length of the cell. Remarkably, nuclear translocation happens quickly over the course of 1-2 post-natal days, coinciding with the onset of hearing. The movement of the nucleus likely signals the closing of a critical period correlated with the forming and refining of synapses at the onset of hearing. Significance StatementThe misplacement of a cells nucleus has been implicated in hearing, vision, and muscular pathologies. In this study, we report a remarkably abrupt change in nuclear position in cochlear inner hair cells that coincides with the onset of hearing in rats, when hair cells switch from producing sensory-independent action potentials to sensory-dependent graded potentials. This work suggests that post-mitotic nuclear migration may be critical to the final phase of post-natal development in mammalian hearing.