Hair cells are the receptor cells of the auditory and vestibular systems as well as of the lateral line. These specialized cells are surmounted by bundles of actin-filled projections that confer mechanosensitivity along a specific axis. The correct interpretation of mechanical stimuli thus depends on correctly coordinated planar cell polarity (PCP). Despite this, the establishment of hair-cell orientation is not well understood. In the neuromast, the sensory organ of the lateral line, hair-cell precursors divide to produce sister cells that consistently develop opposite planar orientations. The asymmetric localization of the PCP factor van Gogh- like 2 (Vangl2), however, does not differ between the sister cells. The core PCP genes are therefore insufficient to specify hair-cell polarity. Prior to the development of hair bundles, the sister cells resulting from mitosis of a precursor undergo rotational rearrangements. Previous work demonstrated that overexpression of Vangl2 or inhibition of Notch signaling interferes with these movements and causes hair cells to aberrantly adopt a uniform alignment. These results suggest that precursor division confers an asymmetry upon sister cells and necessitates that they rotate into position. Such an asymmetry would override an intrinsic preference for uniform orientation. The machinery that governs asymmetric cell division may therefore play a role in planar cell polarity. No cell-fate determinants have yet been shown to influence hair-cell polarity, but preliminary results demonstrate that the experimental knockdown of a centriole-associated protein may result in misoriented hair bundles.
The aim of this project is to further test the role of centriole inheritance in hair-cell PCP and rearrangements. Live imaging and statistical analysis will determine the effects of knockdown on rearrangements. Pulse-chase labeling of the fluorescent protein Kaede fused to a centriole-associated protein may delineate a correlation between centriole age and hair-cell polarity. Additionally, fluorescent reporter molecules and in situ hybridization may elucidate the signaling pathways that affect hair-cell polarization. Because basal-body positioning correlates with hair-bundle orientation, an understanding of these signals has implications for understanding the mechanosensitivity of hair cells.
The establishment of correct planar orientation is essential for the sensory function of hair cells, the receptor cells of the mammalian inner ear and zebrafish lateral line. Although cellular orientation is therefore crucial for human hearing, the process is not well understood. This project accordingly aims to elucidate mechanisms regulating planar polarity by investigating the rotational rearrangements that lateral-line hair cells undergo prior o polarization.
|Dow, Eliot; Siletti, Kimberly; Hudspeth, Albert J (2015) Cellular projections from sensory hair cells form polarity-specific scaffolds during synaptogenesis. Genes Dev 29:1087-94|