RT Journal Article
SR Electronic
T1 Large Membrane Domains in Hair Bundles Specify Spatially Constricted Radixin Activation
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 4600
OP 4609
DO 10.1523/JNEUROSCI.6184-11.2012
VO 32
IS 13
A1 Zhao, Hongyu
A1 Williams, Diane E.
A1 Shin, Jung-Bum
A1 Brügger, Britta
A1 Gillespie, Peter G.
YR 2012
UL http://www.jneurosci.org/content/32/13/4600.abstract
AB The plasma membrane of vertebrate hair bundles interacts intimately with the bundle cytoskeleton to support mechanotransduction and homeostasis. To determine the membrane composition of bundles, we used lipid mass spectrometry with purified chick vestibular bundles. While the bundle glycerophospholipids and acyl chains resemble those of other endomembranes, bundle ceramide and sphingomyelin nearly exclusively contain short-chain, saturated acyl chains. Confocal imaging of isolated bullfrog vestibular hair cells shows that the bundle membrane segregates spatially into at least three large structural and functional domains. One membrane domain, including the stereocilia basal tapers and ∼1 μm of the shaft, the location of the ankle links, is enriched in the lipid phosphatase PTPRQ (protein tyrosine phosphatase Q) and polysialylated gangliosides. The taper domain forms a sharp boundary with the shaft domain, which contains the plasma membrane Ca2+-ATPase isoform 2 (PMCA2) and phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2]; moreover, a tip domain has elevated levels of cholesterol, PMCA2, and PI(4,5)P2. Protein mass spectrometry shows that bundles from chick vestibular hair cells contain a complete set of proteins that transport, synthesize, and degrade PI(4,5)P2. The membrane domains have functional significance; radixin, essential for hair-bundle stability, is activated at the taper–shaft boundary in a PI(4,5)P2-dependent manner, allowing assembly of protein complexes at that site. Membrane domains within stereocilia thus define regions within hair bundles that allow compartmentalization of Ca2+ extrusion and assembly of protein complexes at discrete locations.