Activation and organization of the actomyosin cytoskeleton in the C. elegans spermatheca

Abstract

Nonmuscle myosin II (NMII) is expressed in all eukaryotic cells and interacts with the polymer F-actin to drive contraction in cells. Cell contractility underlies many biological processes including wound healing, developmental morphogenesis, cell migration, and cell division. We are interested in understanding how multicellular tissues coordinate NMII-driven contractility across multiple cells in time and space. Here we use the C. elegans spermatheca, a contractile tube of myoepithelial cells to understand how myosin activity is regulated in time and space, and how actin-organizing proteins function to organize the cytoskeleton for efficient contraction. This work builds on cell culture studies that lack the relevant biomechanical and biochemical cues of an in vivo system. We identify a myosin light chain kinase, MLCK-1, which phosphorylates and activates NMII to drive cell contractility. MLCK-1 and Rho kinase, LET-502, are expressed at different levels across the spermatheca to allow for different amounts of contraction in different regions of the tissue. We also find that hydrogen peroxide is produced at different levels across the spermatheca, which we think contributes to differences in contractility across the tissue. Hydrogen peroxide inhibits Rho, and thus contractility, by oxidizing a conserved cysteine residue within its GTP-binding pocket. Lastly, we find that filamin, an actin crosslinker, not only regulates the organization of the actin network, but is also required for correct spatial localization of myosin. We use the fln-1 mutants to uncover a role for the linker of nucleoskeleton and cytoskeleton (LINC) complex and have identified several new actin stabilizing proteins. Together, this dissertation describes how the spermatheca, a model for multicellular tube, can localize and fine tune myosin activity across many a tissue, and how the actin network is anchored and spaced such that the overall tissue contractility is organized and coordinated.--Author's abstract