Abstract
Purpose :
The mouse ocular lens is an excellent vertebrate model system to study hexagonal cell patterning during epithelial cell morphogenesis and differentiation, wherein lens epithelial cells transform from randomly packed cells to hexagon-shaped cells organized into meridional rows. The meridional row cells elongate apically as they differentiate into fiber cells, and fiber cells maintain the hexagon cell shape and cell alignment. Non-muscle myosin IIA (NMIIA) is a motor protein that forms bipolar filaments via anti-parallel associations of rod domains. NMIIA motor domains are located at bipolar filament ends and pull on actin filaments (F-actin) to generate contractile force. Here, we studied the effect of three human disease-related (and cataract-linked) NMIIA mutations on mouse lens cellular organization during epithelial cell morphogenesis and differentiation.
Methods :
We studied genetic knock-in mice with these mutations: NMIIA-R702C motor domain mutation (reduces ATPase hydrolysis and F-actin sliding rate without affecting F-actin crosslinking); NMIIA-D1424N and NMIIA-E1841K rod domain mutations (disrupt rod domain associations required for NMIIA filament assembly). We labeled lens cryosections for F-actin to measure fiber cell disorder. Lens whole mount and epithelium flat mounts were stained and imaged by confocal microscopy to visualize F-actin and NMIIA localization in meridional row cells.
Results :
The NMIIA-R702C motor domain mutation has no impact on lens cellular organization. In contrast, both rod domain mutations disrupt hexagon shape and organization of meridional row cells during differentiation. Both rod domain mutations also disrupt lens fiber cell organization, leading to large patches of disordered fiber cells. The NMIIA-E1841K mutation leads to reduced cortical F-actin assembly and redistribution of NMIIA:F-actin fibers from radial to polarized orientation in the basal region of meridional row cells.
Conclusions :
Lens epithelial cell hexagon shape and patterning during fiber cell differentiation depends on the correct location and orientation of actomyosin contractile structures in epithelial cells. We propose that F-actin cortical tension and radially oriented actomyosin fibers contribute to uniform force balances that maintain hexagon cell shape and patterning of lens epithelial cells.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.