Orchestrating nonmuscle myosin II filament assembly at the onset of cytokinesis

Abstract

Contractile forces in the actomyosin cortex are required for cellular morphogenesis. This includes the invagination of the cell membrane during division, where filaments of non-muscle myosin II (NMII) are responsible for generating contractile forces in the cortex. However, how NMII heterohexamers form filaments in vivo is not well understood. To quantify NMII filament assembly dynamics, we imaged the cortex of C. elegans embryos at high spatial resolution around the time of the first division. We show that during the assembly of the cytokinetic ring, both the number of NMII filaments in the cortex increases and more NMII motors are assembled into each filament. These dynamics are influenced by two proteins in the RhoA GTPase pathway, the RhoA dependent kinase LET-502 and the myosin phosphatase MEL-11. We find that these two proteins differentially regulate NMII activity at the anterior and at the division site. We show that the coordinated action of these regulators generates a gradient of free NMII in the cytoplasm driving a net diffusive flux of NMII motors towards the cytokinetic ring. Our work highlights how NMII filament assembly and disassembly dynamics are orchestrated over space and time to facilitate the up-regulation of cortical contractility during cytokinesis. [Media: see text] [Media: see text] [Media: see text] [Media: see text]

Limiting Pool and Actin Architecture Controls Myosin Cluster Sizes in Adherent Cells

“…This concept has been demonstrated in several organelles, such as the flagella (Ludington et al, 2012), centrosomes (Decker et al, 2011), and mitotic spindles (Mitchison et al, 2015). Similarly, structures that depend on the same building blocks can compete for these limited components, as observed with different F-actin architectures (Suarez and Kovar, 2016;Kadzik et al, 2020) and myosin clusters on various actomyosin structures (Beach et al, 2017;Najafabadi et al, 2022). Our paper contributes to this idea by quantitatively demonstrating its applicability in stress fibers of non-muscle cells.…”

MT-125 Inhibits Non-Muscle Myosin IIA and IIB, Synergizes with Oncogenic Kinase Inhibitors, and Prolongs Survival in Glioblastoma

“…In each case, MT-125 significantly impairs Transwell invasion ( p<0.0001 ). NMII is required for cytokinesis, and its inhibition leads to multinucleation and aneuploidy (Newell-Litwa, et al, 2015; Najafabadi, et al, 2022). We found that treating 10 human GBM lines with 5 µM MT-125 for 48 hours produces multinucleation in 12-25% of tumor cells ( Fig.…”

“…Among these are members of the myosin II class, which includes skeletal, smooth, and cardiac myosin II along with three non-muscle myosin II (NMII) paralogs, referred to as NMIIA, IIB, and IIC. NMII plays multiple roles in cell physiology, including motility, cytokinesis, mitochondrial fission, and signaling (Straight, et al, 2003;Garrido-Casado, et al, 2021;Quintanilla, Hammer, and Beach, 2023;Najafabadi, et al, 2022;Stricker, et al, 2013, Kim et al, 2012Zheng et al, 2021). However, these NMII-driven functions are also important in supporting pathological states.…”

Axis convergence inC. elegansembryos

“…Embryos from mothers that are mutant for NOP-1 lack a pseudocleavage furrow (Rose et al, 1995). MEL-11 is a myosin phosphatase (Piekny and Mains, 2002) that suppresses the activity of myosin in the cortex (Najafabadi et al, 2022). RNAi of nop-1 eliminates the pseudocleavage furrow in the embryo (Tse et al, 2012), but cortical flows are also reduced (SI: Figure 3, SI: Figure 4 c, SI: Figure 4 d, SI: subsection 3.1).…”