Abstract
Cadherin 23 (CDH23), a component of tip links in hair cells of vertebrate animals, is essential to mechanotransduction by hair cells in the inner ear. A homolog of CDH23 occurs in hair bundles of sea anemones. Anemone hair bundles are located on the tentacles where they detect the swimming movements of nearby prey. The anemone CDH23 is predicted to be a large polypeptide featuring a short exoplasmic C-terminal domain that is unique to sea anemones. Experimentally masking this domain with antibodies or mimicking this domain with free peptide rapidly disrupts mechanotransduction and morphology of anemone hair bundles. The loss of normal morphology is accompanied, or followed by a decrease in F-actin in stereocilia of the hair bundles. These effects were observed at very low concentrations of the reagents, 0.1–10 nM, and within minutes of exposure. The results presented herein suggest that: (1) the interaction between CDH23 and molecular partners on stereocilia of hair bundles is dynamic and; (2) the interaction is crucial for normal mechanotransduction and morphology of hair bundles.
Highlights
Hair bundles are the mechanoreceptor apparatus of hair cells
Cadherin 23 (CDH23) antibodies bind to anemone hair bundles The CDH23 antibody labeled hair bundles in N. vectensis (Figure 1A) such that punctate fluorescence was observed predominately in the distal half of hair bundle length
CDH23 is an important component of tip links, extracellular linkages that participate in mechanotransduction of hair cells in vertebrate animals [16,18,34]
Summary
Hair bundles are the mechanoreceptor apparatus of hair cells. Hair bundles consist of stereocilia, evaginations of the plasma membrane filled with actin filaments. Hair bundles transduce signals when the hair bundle is deflected. An extracellular current was measured near the distal end of moving hair bundles [5]. Later experiments performed with the iontophoretic application of gentamicin, an aminoglycoside antibiotic that blocks mechanotransduction, indicated that the mechanotransduction channels are likely to be located near the tips of the stereocilia [6]. According to the gating spring model, when a hair bundle is deflected in a positive direction (i.e., toward the taller stereocilia), mechanotransduction channels open rapidly to allow a cation influx. Because stretching the gating-spring raises the energy level of the closed state, the mechanotransduction channel’s open state is energetically favored. An estimated 15–20 percent of the mechanotransduction channels are open because of significant resting tension on the gating spring. The resting mechanotransduction current was observed at 20,40% of maximum instead of at zero [11]
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