Key result
Local myosin monomer levels and established filaments potentiate non-muscle myosin 2 assembly, with assembling myosin being approximately 100 times more likely to incorporate into existing structures than to form nascent clusters.
Why the study?
The ability to dynamically assemble contractile networks is required throughout cell physiology, but the biophysical mechanisms regulating non-muscle myosin 2 filament assembly in living cells are lacking.
This study establishes that local myosin monomer levels and established filaments, rather than specific actin architectures, drive the assembly and amplification of non-muscle myosin 2 networks.
No immediate clinical implications; leaves open whether monomer-filament potentiation drives myosin networks in human cardiovascular cells.
The ability to dynamically assemble contractile networks is required throughout cell physiology, yet the biophysical mechanisms regulating non-muscle myosin 2 filament assembly in living cells are lacking. Here we use a suite of dynamic, quantitative imaging approaches to identify deterministic factors that drive myosin filament appearance and amplification. We find that actin dynamics regulate myosin assembly, but that the actin architecture plays a minimal direct role. Instead, remodeling of actin networks modulates the local myosin monomer levels and facilitates assembly through myosin:myosin driven interactions. Using optogenetically controlled myosin, we demonstrate that locally concentrating myosin is sufficient to both form filaments and jump-start filament amplification and partitioning. By counting myosin monomers within filaments, we demonstrate a myosin-facilitated assembly process that establishes sub-resolution filament stacks prior to partitioning into clusters that feed higher-order networks. Together these findings establish the biophysical mechanisms regulating the assembly of non-muscle contractile structures that are ubiquitous throughout cell biology.
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Quintanilla et al. (2023) studied this question. Optogenetic and pharmacological manipulation of actin and myosin was evaluated on NM2 filament assembly and partitioning. Local myosin monomer levels and established filaments potentiate non-muscle myosin 2 assembly, with assembling myosin being approximately 100 times more likely to incorporate into existing structures than to form nascent clusters.
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