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The Journal of Neuroscience, November 1, 1998, 18(21):8637-8647
Localization of Myosin-I near Both Ends of Tip Links in Frog
Saccular Hair Cells
Jesús A.
García1,
Ann G.
Yee2,
Peter G.
Gillespie3, and
David P.
Corey2, 4
1 Program in Neuroscience and 2 Department
of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, 3 Departments of Physiology and Neuroscience, The Johns
Hopkins University, Baltimore, Maryland 21205, and 4 Howard
Hughes Medical Institute and Neurobiology Department, Massachusetts
General Hospital, Boston, Massachusetts 02114
Current evidence suggests that the adaptation motor of
mechanoelectrical transduction in vertebrate hair cells is myosin-I . Previously, confocal and electron microscopy of bullfrog saccular hair
cells using an anti-myosin-I antibody labeled the tips of stereocilia. We have now done quantitative immunoelectron microscopy to
test whether myosin-I is enriched at or near the side plaques of tip
links, the proposed sites of adaptation, using hair bundles that were
serially sectioned parallel to the macular surface. The highest
particle density occurred at stereocilia bases, close to the cuticular
plate. Also, stereocilia of differing lengths had approximately the
same number of total particles, suggesting equal targeting of
myosin-I to all stereocilia. Finally, particles tended to clump in
clusters of two to five particles in the distal two-thirds of
stereocilia, suggesting a tendency for self-assembly of
myosin-I.
As expected from fluorescence microscopy, particle density was high in
the distal 1 µm of stereocilia. If myosin-I is the adaptation
motor, a difference should exist in particle density between regions
containing the side plaque and those excluding it. Averaging of
particle distributions revealed two regions with approximately twice
the average density: at the upper ends of tip links in a 700-nm-long
region centered ~100 nm above the side plaque, and at the lower ends
of tip links within the tip plaques. Controls demonstrated no such
increase. The shortest stereocilia, which lack side plaques, showed no
concentration rise on their sides. Thus, the specific localization of
myosin-I at both ends of tip links supports its role as the
adaptation motor.
Key words:
hair cell; myosin-I; adaptation; auditory; vestibular; electron microscopy
Copyright © 1998 Society for Neuroscience 0270-6474/98/18218637-11$05.00/0
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