Biology subjects

ROBIN, F. B.

Publications and source records attributed to ROBIN, F. B..

3 recordsLinked to original sources

bioRxiv2026

Persistent and recyclable myosin II minifilaments drive cortical contractility in the early C. elegans embryo

Non-muscle myosin II is a key regulator of cell and tissue morphogenesis, yet the cortical dynamics of myosin minifilaments in vivo remain poorly understood. Here, we combine SIM-TIRF and single-molecule TIRF microscopy to characterize the structure and dynamics of myosin minifilaments in an early developing embryo. High-temporal-resolution SIM-TIRF imaging revealed diverse minifilament behaviors, including partition-like events, long-range alignment of multiple minifilaments into collective structures we called proto-stress fibers, partial unbinding, and sequential unbinding and rebinding to the cortex. Photoconversion experiments showed that minifilaments persist as intact units after cortical unbinding, diffuse through the cytoplasm, and can be recycled over long distances rather than disassembling upon detachment. Despite these dynamic behaviors, minifilaments are predominantly stationary when bound to actin. Numerical simulations demonstrated that this static behavior is essential to sustain cortical stress within a continuously remodeling actin network. Using myosin motor-domain mutants, we further investigated the contribution of motor activity to these behaviors. Together, our results reveal that myosin minifilaments can persist as stable units while cycling between the cortex and cytoplasm, and that their predominantly static behavior when bound to actin enables sustained force generation in a continuously renewing cortical network. These findings provide new insights into myosin organization, recycling, and force generation during early embryonic development.

cell biology↗

bioRxiv2026

Kinetic Control of Out-Of-Equilibrium Dynamics in the RhoA Signaling Cascade Shapes Actomyosin Contractility

Cellular functions rely on the precise timing of signal transmission through sequential activation cascades, yet the origin and functional role of signaling delays remain poorly understood. Here, we dissect the temporal organization of the RhoA signaling cascade during pulsed actomyosin contractility in the early C. elegans embryo. We uncover a stereotypical delay between upstream RhoA/ROCK activation and downstream myosin II recruitment. Using TIRF single-molecule microscopy, we show that this delay arises from binding and unbinding kinetics of myosin rather than from slow biochemical reactions. A simple and versatile kinetic model parameterized by these measurements accurately predicts the temporal evolution of myosin accumulation and reveals active control of the dynamic range of the cascade. Perturbing actin and myosin turnover experimentally confirms these predictions, and numerical simulations show that the delay between actin and myosin plays a critical role in force deployment during pulsed contraction. Together, our results indicate that kinetic delays in signaling cascades are not simply tolerated during morphogenesis, but actively shape force deployment in the cell.

developmental biology↗

bioRxiv2020

Rapid assembly of a polar network architecture by formins downstream of RhoA pulses drives efficient cortical actomyosin contractility

SO_SCPLOWUMMARYC_SCPLOWActin network architecture and dynamics play a central role in cell contractility and tissue morphogenesis. Pulsed contractions driven by RhoA represent a generic mode of actomyosin contractility, but the mechanisms underlying (1) how their specific architecture emerges, and (2) how this architecture supports the contractile function of the network, remain unclear. Here, we combine quantitative microscopy, single-molecule imaging, numerical simulations and simple mathematical modelling, to explore the dynamic network architecture underlying pulsed contraction. We show that during pulsed contractions, two subpopulations of formins are recruited by RhoA from the cytoplasm and bind to the cell surface in the early C. elegans embryo: recruited formins, a functionally inactive population, and elongating formins, which actively participate in actin filaments elongation. Focusing on formin dynamics during pulses, we show that minority elongating formins precede recruited formins, a kinetic dynamics compatible with formins capturing and rapidly saturating barbed ends available for filament elongation. We then show that these elongating formins assemble a polar network of actin, with barbed ends pointing out of the pulse, pointing to a kinetic rather than mechanical control of network architecture. Finally, our numerical simulations demonstrate that this geometry favors rapid network contraction. Our results thus show that formins saturate available actin filaments barbed ends and convert a local, biochemical gradient of RhoA activity into a polar network architecture, thereby driving rapid and efficient network contractility, an important evolutionary feature in a metazoan with a rapid embryonic cell cycles. HO_SCPLOWIGHLIGHTSC_SCPLOWO_LIThe formin CYK-1 drives actin network assembly during RhoA-driven pulses C_LIO_LIThe process is extremely rapid, with a formin-based actin elongation rate higher than 1.3 m{middle dot}s-1 C_LIO_LIA barbed-end saturation mechanism allows for responsive F-actin assembly C_LIO_LIRapid and responsive F-actin elongation results in the assembly of aster-like polar actin networks C_LIO_LINumerical simulations show network polarity drives very efficient network contractility C_LI

cell biology↗