Development and Protein Composition of the Striated Organelle and Spectrin Localization in the Inner Ear

The striated organelle (SO) is an intriguing cytoskeletal structure that has consistently been observed to occur in the subcuticular region of inner ear vestibular type I and type II hair cells, and cochlear inner (but not outer) hair cells, in most vertebrates. Its function is still unknown, and what little has been reported of its protein composition consists largely of multifunctional, common, everyday proteins (such as α-II-spectrin and F-actin) whose inclusion in the SO make-up offers no obvious clues from which we can infer function. What is known from previous studies, however, is that the SO has been observed to occur in both normal and diseased hair cells; is intricately linked to microtubules, stereociliar rootlets and ‘giant’ apical mitochondria; and is composed of alternating bands of filaments 10nm and 35nm thick that lie 65nm apart. Going forward the primary objectives of this work were to: 1) Determine some of the major proteins making up the organelle by identifying those interacting with alpha-II-spectrin; 2. Determine the timeline of the SO appearance in the hair cells by tracking the developmental expression of αII spectrin; and 3) map all the beta spectrins to identify the expression patterns and the β-spectrin partner for αII-spectrin, which could then be incorporated into 1) and 2) above. To accomplish these aims, I primarily relied on and performed immunohistochemistry (confocal and electron microscopy), western blots, immunoprecipitations, and liquid chromatography-mass spectroscopy for adata acquisition. From my data it appears that βII-spectrin is the pairing partner to αII-spectrin in the cuticular plate, striated organelle and lateral membranes of all vestibular cell types except type I hair cells; striated organelle biogenesis is postnatal, occurring between postnatal days 3 and 4 (P3-P4), and is preceded by maturation of the cuticular plate; all seven mammalian spectrin subunits occur in the inner ear sensory epithelium. Our work was limited to structural characterization and function of the SO still remains unresolved.