Abstract
Purpose :
Lifelong transparency and focusing ability of the lens depends on the precise alignment of equatorial epithelial cells that differentiate into secondary fiber cells during lens development and morphogenesis. During this process, the equatorial epithelial cells transform from randomly packed cells into precisely aligned, hexagonally shaped meridional row cells that elongate to form the hexagonally packed, long fiber cells. Here, we investigate the function of Non-muscle Myosin IIA (NMIIA) (Myh9) in regulating equatorial epithelial cell alignment (meridional row cells) & fiber cell morphogenesis.
Methods :
We used genetic knock-in mice to study two Myh9 mutations, R702C in the motor domain and E1841K in the rod domain. The R702C mutation impairs motor function and contractility, while the E1841K mutation disrupts bipolar filament assembly. Images of dissected lenses were acquired using a digital camera to check for cataracts. Lens equatorial cryosections and whole mounts were stained with fluorescent phalloidins (actin filaments; F-actin) and Hoechst (nuclei) and imaged by confocal microscopy to investigate the cellular organization.
Results :
Neither mutation causes cataracts or opacities, and no major defects in cell organization are observed in R702C mutant mice. By contrast, the E1841K mutation results in disordered fiber cell packing in equatorial cryosections. Imaging of the equatorial epithelium and peripheral fiber cells in E1841K lenses also reveals meridional row misalignment, and peripheral fiber cell disorder, and variable widths. This indicates that epithelial cells with the E1841K mutation become misaligned during their initial rearrangement into meridional rows, with misalignment persisting during fiber cell elongation.
Conclusions :
Disrupted bipolar filament assembly, due to the E1841K mutation, causes misaligned meridional row alignment and disordered fiber cells, while impaired force generation, due to the R702C mutation, does not. Since R702C can still exert tension by cross-linking F-actin, we propose that actomyosin organization, conferred by bipolar filaments’ cross-linking F-actin, is important for cell tension and meridional row alignment. These results indicate a novel function of NMIIA in regulating the alignment of lens epithelial cells during their transformation into precisely aligned and hexagonally packed fiber cells.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.