Figure 4: Calcium transients in stereocilia precede the maturation of the MET complex.

A) A standard deviation projection of a time-lapse that shows spontaneous calcium transients occurring in stereocilia inner hair cells at P0, prior to the maturation of the MET complex. B) Immature microvilli cover the apical surface of early post-natal hair cells as shown in the SEM image (left). Only a few of these microvilli precursors elongate to become stereocilia while the rest disassemble and are integrated into the cell membrane. These microvilli also exhibit spontaneous calcium transients as shown in the standard deviation projection (right) of P4 inner hair cells, although their occurrence is much rarer than those in stereocilia. C) Transients in microvilli precursors occur on the same timescale as in stereocilia. Shown are traces for a stereocilium (blue) and a precursor (red). The timeframes for the traces have been shifted such that t = 0 when the transient is first seen.