Inner ear supporting cells: Rethinking the silent majority

• Supporting cells are required for cell patterning, planar cell polarity, and synaptogenesis in developing sensory epithelia.
• In mature sensory epithelia, supporting cells preserve the structural integrity of the sensory organs, modulate ion and small molecule homeostasis, and maintain the accessory extracellular matrices that enable hair cell mechanotransduction.
• Supporting cells clear damaged hair cells and regenerate hair cells in injured sensory epithelia.

Sensory epithelia of the inner ear contain two major cell types: hair cells and supporting cells. It has been clear for a long time that hair cells play critical roles in mechanoreception and synaptic transmission. In contrast, until recently the more abundant supporting cells were viewed as serving primarily structural and homeostatic functions. In this review, we discuss the growing information about the roles that supporting cells play in the development, function and maintenance of the inner ear, their activities in pathological states, their potential for hair cell regeneration, and the mechanisms underlying these processes.