Superresolution microscopy reveals actomyosin dynamics in medioapical arrays

• Published in: Molecular biology of the cell Vol. 33; no. 11; pp. 1 - ar94
• Main Authors: Moore, Regan P, Fogerson, Stephanie M, Tulu, U. Serdar, Yu, Jason W, Cox, Amanda H, Sican, Melissa A, Li, Dong, Legant, Wesley R, Weigel, Aubrey V, Crawford, Janice M, Betzig, Eric, Kiehart, Daniel P
• Format: Journal Article
• Language: English
• Published: American Society for Cell Biology 15-09-2022; The American Society for Cell Biology
• Subjects: Actin; Analysis; Anisotropy; Drosophila; Identification and classification; Methods; Microscope and microscopy; Muscle proteins; Myosin; Properties; United States
• ISSN: 1059-1524; 1939-4586
• DOI: 10.1091/mbc.E21-11-0537

Superresolution microscopy produced images of individual actin and myosin filaments and their three-dimensional distribution in medioapical arrays of cells in developing embryos. Arrays are part of a modified cell cortex that condenses and relaxes with isotropic and anisotropic contraction and expansion-they are recruited to ameliorate cell bulging.
Arrays of actin filaments (F-actin) near the apical surface of epithelial cells (medioapical arrays) contribute to apical constriction and morphogenesis throughout phylogeny. Here, superresolution approaches (grazing incidence structured illumination, GI-SIM, and lattice light sheet, LLSM) microscopy resolve individual, fluorescently labeled F-actin and bipolar myosin filaments that drive amnioserosa cell shape changes during dorsal closure in Drosophila. In expanded cells, F-actin and myosin form loose, apically domed meshworks at the plasma membrane. The arrays condense as cells contract, drawing the domes into the plane of the junctional belts. As condensation continues, individual filaments are no longer uniformly apparent. As cells expand, arrays of actomyosin are again resolved—some F-actin turnover likely occurs, but a large fraction of existing filaments rearrange. In morphologically isotropic cells, actin filaments are randomly oriented and during contraction are drawn together but remain essentially randomly oriented. In anisotropic cells, largely parallel actin filaments are drawn closer to one another. Our images offer unparalleled resolution of F-actin in embryonic tissue, show that medioapical arrays are tightly apposed to the plasma membrane and are continuous with meshworks of lamellar F-actin. Medioapical arrays thereby constitute modified cell cortex. In concert with other tagged array components, superresolution imaging of live specimens will offer new understanding of cortical architecture and function.