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Vasanth Rao, Rupalatha Maddala, Mark D Walters, Vann Bennett; Ankyrin-B Haploinsufficient Lenses Uncover the Importance of Membrane Subdomain Organization for Fiber Cell Hexagonal Packing and Mechanical Properties. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1683.
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© ARVO (1962-2015); The Authors (2016-present)
Fiber cell hexagonal symmetry, membrane organization and tensile properties are considered to be critical for lens architecture, transparency and deformability. The molecular determinants of membrane organization that govern these lens characteristics, however, are not well defined. In this study, we examined the 3-D organization of various membrane and membrane-associated proteins in normal and Ankyrin-B deficient (AnkB-/+) mouse lenses in the context of fiber cell geometry and tensile properties.
Paraffin-embedded equatorial lens sections derived from the wild type (WT) and AnkB-/+ mice were evaluated for the distribution profile of Ank-B & G, β-spectrin, β-actin, periaxin, Connexin-50, Aquaporin-0, NrCAM, ponsin, β-dystroglycan and filensin using a Zeiss 780 inverted confocal microscope in conjunction with Volocity 3D construction software. Changes in lens stiffness were evaluated using a Micro-strain analyzer.
In WT lenses AnkB & G are distributed in distinct subdomains throughout the fiber cell membrane including the long and short arms. High resolution confocal images using 3D reconstruction reveal a discrete distribution pattern of β-actin, ponsin and periaxin, which localize predominantly to the tricellular junctions of fiber cells. β-spectrin and NrCAM exhibit intense staining throughout the short arms relative to their distribution within the long arms. In contrast, β-dystroglycan, connexin-50 and filensin cluster into large domains at the center of long arms of fiber cells. Aquaporin-0 is distributed throughout the fiber cell. The AnkB-/+ mice show a slight increase in lens weight but remain clear. However, these lenses reveal disruption of hexagonal geometry of fiber cells. Additionally, the membrane organization, protein levels and expression of above described proteins along with L-type calcium channels and myosin II phosphorylation were significantly disrupted in the AnkB-/+ mouse lenses. These lenses show a significant decrease in stiffness compared to WT lenses.
Taken together, this study reveals that Ankyrin-B-based membrane subdomain organization determines mechanical properties and hexagonal cell packing in the lens.
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