Cochlear outer hair cells undergo an apical circumference remodeling constrained by the hair bundle shape.

Raphael Etournay (1, 2) , Léa Lepelletier (3, 2) , Jacques Boutet de Monvel (2) , Vincent Michel (2) , Nadège Cayet (4) , Michel Leibovici (5, 2) , Dominique Weil (2) , Isabelle Foucher (6, 2, 7) , Jean-Pierre Hardelin (2) , Christine Petit (2)

1 MPI-CBG - Max Planck Institute of Molecular Cell Biology and Genetics
2 Collège de France - Chaire Génétique et physiologie cellulaire
3 UPD7 - Université Paris Diderot - Paris 7
4 Microscopie Ultrastructurale (Plate-forme)
5 Département de Biologie du Développement
6 UP11 - Université Paris-Sud - Paris 11
7 DEPSN - Développement, évolution et plasticité du système nerveux

Epithelial cells acquire diverse shapes relating to their different functions. This is particularly relevant for the cochlear outer hair cells (OHCs), whose apical and basolateral shapes accommodate the functioning of these cells as mechano-electrical and electromechanical transducers, respectively. We uncovered a circumferential shape transition of the apical junctional complex (AJC) of OHCs, which occurs during the early postnatal period in the mouse, prior to hearing onset. Geometric analysis of the OHC apical circumference using immunostaining of the AJC protein ZO1 and Fourier-interpolated contour detection characterizes this transition as a switch from a rounded-hexagon to a non-convex circumference delineating two lateral lobes at the neural side of the cell, with a negative curvature in between. This shape tightly correlates with the 'V'-configuration of the OHC hair bundle, the apical mechanosensitive organelle that converts sound-evoked vibrations into variations in cell membrane potential. The OHC apical circumference remodeling failed or was incomplete in all the mouse mutants affected in hair bundle morphogenesis that we tested. During the normal shape transition, myosin VIIa and myosin II (A and B isoforms) displayed polarized redistributions into and out of the developing lobes, respectively, while Shroom2 and F-actin transiently accumulated in the lobes. Defects in these redistributions were observed in the mutants, paralleling their apical circumference abnormalities. Our results point to a pivotal role for actomyosin cytoskeleton tensions in the reshaping of the OHC apical circumference. We propose that this remodeling contributes to optimize the mechanical coupling between the basal and apical poles of mature OHCs.

Mots clés: Animals; Cilia; Cochlea; Ear; Inner; Goats; Hair Cells; Auditory; Outer; Mice; Microscopy; Electron; Scanning; Neurons; Organ of Corti

Domaines: Biologie cellulaire

Raphael Etournay, Léa Lepelletier, Jacques Boutet de Monvel, Vincent Michel, Nadège Cayet, et al.. Cochlear outer hair cells undergo an apical circumference remodeling constrained by the hair bundle shape.. Development (Cambridge, England), 2010, 137 (8), pp.1373-83. ⟨10.1242/dev.045138⟩. ⟨pasteur-01545828⟩