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V. M. Fowler, M. Dressler, R. B. Nowak; Tropomodulin1 is Dispensable for Establishment But Not Maintenance of Fiber Cell Packing Geometry as Cells Mature in the Lens Cortex. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4611.
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© ARVO (1962-2015); The Authors (2016-present)
Tropomodulin 1 (Tmod1) is a tropomyosin and actin binding protein that stabilizes the spectrin membrane skeleton in lens fiber cells and controls their hexagonal packing geometry (Nowak et al., 2009, J. Cell Biol. 186:915-928). To investigate the origins of disrupted hexagonal packing observed in lens fiber cells of a Tmod1 knockout mouse we compared packing geometries of fiber cells at different stages of maturation.
To quantify fiber cell packing order in the lens cortex, one-month-old mouse lenses were fixed, cryosectioned at the equator and stained with fluorescent-phalloidin to outline fiber cell membranes for confocal microscopy. Nearest neighbor analysis was carried out using a custom-designed program. Sizes of disordered cell patches and their location with reference to the epithelium were measured in ImageJ. To investigate packing order during the transition from epithelial to fiber cells, living lenses were stained with Hoechst for whole-mount confocal microscopy, and image stacks of epithelial and differentiating fiber cell nuclei at the equator were reconstructed in Volocity.
Nearest neighbor analysis of the lens cortex shows patches of disordered fiber cells. Disruption of hexagonal packing does not arise during its establishment when the epithelial cells line up and differentiate to form fiber cells, but rather during fiber cell maturation as the cells move inwards in the lens cortex. Higher disorder in Tmod1-/- lenses compared to Tmod1+/+ lenses is caused by larger areas of individual patches of disordered fiber cells. However, the incidence of disordered patches in the lens cortex in the presence and absence of Tmod1 is similar. We present a possible mechanism explaining this through the influence of physical stresses inside the lens.
Tmod1 stabilization of the spectrin-based membrane skeleton is necessary to maintain hexagonal packing of fiber cells under the influence of physical stress.
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