Controlling contractile instabilities in the actomyosin cortex

Abstract

The actomyosin cell cortex is an active contractile material for driving cell- and tissue morphogenesis. The cortex has a tendency to form a pattern of myosin foci, which is a signature of potentially unstable behavior. How a system that is prone to such instabilities can rveliably drive morphogenesis remains an outstanding question. Here, we report that in the Caenorhabditis elegans zygote, feedback between active RhoA and myosin induces a contractile instability in the cortex. We discover that an independent RhoA pacemaking oscillator controls this instability, generating a pulsatory pattern of myosin foci and preventing the collapse of cortical material into a few dynamic contracting regions. Our work reveals how contractile instabilities that are natural to occur in mechanically active media can be biochemically controlled to robustly drive morphogenetic events.DOI: http://dx.doi.org/10.7554/eLife.19595.001

Novel cytokinetic ring components drive negative feedback in cortical contractility

“…Therefore, we conclude that GCK-1/CCM-3 are novel components of negative feedback in the cytokinetic ring. These findings advance the growing body of work showing that contractile networks in cells are not only activated by positive regulation, but also contain structural "brakes" and regulatory time-delayed negative feedback important for turnover and dynamics (Bement et al, 2015;Bischof et al, 2017;Dorn et al, 2016;Goryachev et al, 2016;Khaliullin et al, 2018;Michaux et al, 2018;Nishikawa et al, 2017).…”

“…This behavior has been increasingly used to study feedback loops in the regulation of contractility. During pulsed contractility, active RhoA recruits not only the actomyosin cytoskeleton, but also negative regulators of contractility, which in turn complete a time delayed negative feedback loop (Michaux et al, 2018;Naganathan et al, 2018;Nishikawa et al, 2017;Reymann et al, 2016). GCK-1/CCM-3 are implicated in negatively regulating RhoA (Borikova et al, 2010;Louvi et al, 2014;Zheng et al, 2010) and Figure 5G), but it is unknown whether they participate in time-delayed negative feedback.…”

Joint Motion Estimation and Source Identification using Convective Regularisation with an Application to the Analysis of Laser Nanoablations

“…One difficulty in abovementioned approaches is that the observed structures often have a short life time and are being degraded during the observation, while new structures of the same type are being created [47]. Indeed, these molecular structures, and thus their fluorescent signal response, can be described by an advection-reaction equation rather than pure advection [42]. The signal variations due to reaction are a source of error in the estimation of motion that we propose to address in this paper.…”

“…Beyond the need of measurements of dense velocities of moving fluorescentlylabelled molecular structures that prove robust with respect to the reaction term, it is of general interest to quantify the reaction term itself [42], and of general interest to extract information about all the physical quantities and processes, such as diffusion, that govern the observed tissue flow. For this, an accurate estimation of the velocity field corresponding to the time evolution of the distribution of fluorescent molecules is crucial [42,47]. The laser ablation is applied at frame number five, i.e.…”

Emergence of Directional Actomyosin Flows from Active Matter Vibrations

“…Despite the omnipresent functions and implications of cortical actomyosin motions and flows, the exact molecular origins and fundamental determinants of these phenomena are far from being understood. In many eukaryotic model systems, myosin motors acting on actin filaments are proposed to play a key role in driving actomyosin dynamics in cytokinetic rings and cortical actomyosin flows (1,4,(7)(8)(9). Distinct manipulation of myosin and actin independent of other cellular processes is challenging, since they both are functionally highly integrated cellular proteins.…”