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The ultrastructure of stereociliary cross-links
Hearing
Research,
22 (1986)
79
19
Elsevier
The ultrastructure
of stereociliary cross-links
D.N. Furness, CM. Hackney and E.F. Evans Department
of Communication
and Neuroscience,
University
of Keele, Keele, Staflordshire
ST.5 SBG, U.K.
The cross-finks betweer~ stereo&a on guinea pig c~~hleiir hair cells have been examined using high resolution scanning (SEM) and transmission electron microscopy (TEM] confirming recent descriptions of these structures (Bredburg et al.. 1972; Flock, 1977; Osborne et al., 1984; Pickles et al., 1984). New observations have also been made (Fumess and Hackney, 1985). Links from the tips of shorter stereocilia to the side of the adjacent taller stereocilia (upward-pointing), between stereocilia of the same row (side-to-side), and between adjacent rows (row-to-row), have been observed on inner and outer hair cells in material fixed using (1) ~~~~dehyde only, (2) ~ut~aldehyde/os~u~ and (3) the ~~urn/t~~~~hydr~d~ coating technique (Heywood and Resnick, 1981). The omission of osmium during fixation is not essential to preserve the links. Different buffering conditions may be responsible for the disparity between our observations and those made previously (Osborne et al., 1984). In SEM, side-to-side and row-to-row links consist of discrete bridges which vary in their degree of regularity but which occur along most of the stereociIium length. In TEM, these links consist of a number of 3-12 nm strands and form a regular hexagonal lattice within the stereociliary bundle. In SEM, the upward-minting links consist of a single strand up to 300 nm long. They are 15-30 nm wide in gold-coated material, but 3-12 nm in diameter in os~um/~~bohy~~de~at~ material. In TEM, the strands are 2-3 mn wide. Each end is associated with electron-dense material, which lies between the stereociliary membrane and the actin filament bundle, both at the tip of the shorter stereo&urn and at the side of the taller stereocilium. lt has been suggested that the upward-pointing links may be the site of transduction (Pickles et al., 1984). Our observation of membrane specializations associated with the links supports this contention, but it is clear that further structural, biochemical and micromechanical evidence is necessary before the role of the cross-links can be elucidated. This research was supported by a grant to C.M.H. from the Wellcome Tmst and to E.F.E. from the Medicai Research Council.
References
Bredbur8, G., Ades, H.W. and Engstram, H. (1972): Acta Otolaryngol. Sup@. 301, 3-48. Flock, A. (1977): In: Psychophysics and Physiology of Hearing. pp. U-25. Editors: E.F. Evans and J.P. Wilson. Academic Press, London. Fumess, D.N. and Hackney, CM. (1985): Hearing Res. 18, 177-188.
Heywood, P. and Resnick, S. (1981): Acta Otolaryngol. 91, 183-187. Osborne, M.P., Comis, SD. and Pickles, J.O. (1984): Cell Tissue Res. 237,43-48. Pickles, J.O., Comis, SD. and Osborne, M.D. (1984): Hearing Res. 15, 103-112.
*****
Research,
22 (1986)
79
19
Elsevier
The ultrastructure
of stereociliary cross-links
D.N. Furness, CM. Hackney and E.F. Evans Department
of Communication
and Neuroscience,
University
of Keele, Keele, Staflordshire
ST.5 SBG, U.K.
The cross-finks betweer~ stereo&a on guinea pig c~~hleiir hair cells have been examined using high resolution scanning (SEM) and transmission electron microscopy (TEM] confirming recent descriptions of these structures (Bredburg et al.. 1972; Flock, 1977; Osborne et al., 1984; Pickles et al., 1984). New observations have also been made (Fumess and Hackney, 1985). Links from the tips of shorter stereocilia to the side of the adjacent taller stereocilia (upward-pointing), between stereocilia of the same row (side-to-side), and between adjacent rows (row-to-row), have been observed on inner and outer hair cells in material fixed using (1) ~~~~dehyde only, (2) ~ut~aldehyde/os~u~ and (3) the ~~urn/t~~~~hydr~d~ coating technique (Heywood and Resnick, 1981). The omission of osmium during fixation is not essential to preserve the links. Different buffering conditions may be responsible for the disparity between our observations and those made previously (Osborne et al., 1984). In SEM, side-to-side and row-to-row links consist of discrete bridges which vary in their degree of regularity but which occur along most of the stereociIium length. In TEM, these links consist of a number of 3-12 nm strands and form a regular hexagonal lattice within the stereociliary bundle. In SEM, the upward-minting links consist of a single strand up to 300 nm long. They are 15-30 nm wide in gold-coated material, but 3-12 nm in diameter in os~um/~~bohy~~de~at~ material. In TEM, the strands are 2-3 mn wide. Each end is associated with electron-dense material, which lies between the stereociliary membrane and the actin filament bundle, both at the tip of the shorter stereo&urn and at the side of the taller stereocilium. lt has been suggested that the upward-pointing links may be the site of transduction (Pickles et al., 1984). Our observation of membrane specializations associated with the links supports this contention, but it is clear that further structural, biochemical and micromechanical evidence is necessary before the role of the cross-links can be elucidated. This research was supported by a grant to C.M.H. from the Wellcome Tmst and to E.F.E. from the Medicai Research Council.
References
Bredbur8, G., Ades, H.W. and Engstram, H. (1972): Acta Otolaryngol. Sup@. 301, 3-48. Flock, A. (1977): In: Psychophysics and Physiology of Hearing. pp. U-25. Editors: E.F. Evans and J.P. Wilson. Academic Press, London. Fumess, D.N. and Hackney, CM. (1985): Hearing Res. 18, 177-188.
Heywood, P. and Resnick, S. (1981): Acta Otolaryngol. 91, 183-187. Osborne, M.P., Comis, SD. and Pickles, J.O. (1984): Cell Tissue Res. 237,43-48. Pickles, J.O., Comis, SD. and Osborne, M.D. (1984): Hearing Res. 15, 103-112.
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