Structural basis for mechanical transduction in the frog vestibular sensory apparatus: II. The role of microtubules in the organization of the cuticular plate.

The actin matrix of the cuticular plate, which supports the sensory stereocilia bundle, is coupled to the axial cytoskeleton of the hair cell through a well defined microtubule columnar framework. A collection of axial microtubules in a columnar organization penetrate deep into the dense actin matrix of the cuticular plate. Each microtubule displays at the end a 300-500 nm long fuzzy cap that enmeshes with the actin matrix of the cuticular plate. The microtubule associated proteins MAP-1A and MAP-1B were localized by confocal immunofluorescence to the point of microtubule insertion in the cuticular plate. These proteins are likely components of the microtubule capping structure and may mediate the interaction of the microtubules with the actin matrix. The structural interaction of the microtubules with the cuticular plate provides important mechanical coupling of the transduction apparatus to the axial cytoskeleton of the hair cell.