title: Revealing the structure of stereociliary actin by X-ray nanoimaging.
abstract: Hair cell stereocilia are crucial for hearing and the sense of balance. They include an array of accurately packed, parallel actin filaments and act as levers, which transform mechanical deformation into neuronal signals. The length of vestibular stereocilia reaches several micrometers, whereas, for individual microfilaments, the diameter and therefore the characteristic length scale in the lateral direction is on the order of a few nanometers. These orders of magnitude render X-rays an ideal tool for investigating actin packing, and numerous studies on reconstituted in vitro systems have revealed important information. Here we report on the characterization of intact stereocilia using two nanoscale X-ray techniques. We use X-ray ptychography to image stereocilia with quantitative phase contrast and high dose efficiency, showing stereocilia with diameters and lengths in the expected range. We further employ X-ray nanodiffraction using a nanofocused X-ray beam on the same order of magnitude as the width of a stereocilium. Despite the small probe volume we can clearly visualize the stereocilia bundles. From the individual diffraction patterns we determine the local orientation of the actin structures and can clearly correlate them with the corresponding visible-light fluorescence images. Furthermore, azimuthal integration of individual diffraction patterns reveals distinct intensity curves, showing modulations of the signal, which reflect the relevant length scales and pronounced order in the biological system. The applied techniques are not limited to the studies on stereocilia but have the potential of being applied to many biological and soft-matter systems, in particular if a pronounced degree of order is present.
authors.affiliation: Institute for X-ray Physics, Georg-August-University Göttingen , Göttingen, Germany.
authors.forename: Valeria
authors.initials: V
authors.lastname: Piazza
authors.forename: Britta
authors.initials: B
authors.lastname: Weinhausen
authors.forename: Ana
authors.initials: A
authors.lastname: Diaz
authors.forename: Christian
authors.initials: C
authors.lastname: Dammann
authors.forename: Christian
authors.initials: C
authors.lastname: Maurer
authors.forename: Michael
authors.initials: M
authors.lastname: Reynolds
authors.forename: Manfred
authors.initials: M
authors.lastname: Burghammer
authors.forename: Sarah
authors.initials: S
authors.lastname: Köster
mesh_terms: D000199:Actins / Q000737:chemistry*; D000818:Animals; D018069:Hair Cells, Vestibular / Q000166:cytology; D051379:Mice; D057054:Molecular Imaging / Q000379:methods*; D036103:Nanotechnology / Q000379:methods*; D059547:Stereocilia; D014965:X-Rays
chemical_list: D000199:Actins
keywords: X-ray diffraction; actin bundles; nanofocused beam; nanostructure; ptychography; stereocilia; vestibular sensory hair cells