To cope with continuous physiological and environmental stresses, cells of all sizes require an effective wound repair process to seal breaches to their cortex. Once a wound is recognized, the cell must rapidly plug the injury site, reorganize the cytoskeleton and the membrane to pull the wound closed, and finally remodel the cortex to return to homeostasis. Complementary studies using various model organisms have demonstrated the importance and complexity behind the formation and translocation of an actin ring at the wound periphery during the repair process. Proteins such as actin nucleators, actin bundling factors, actin-plasma membrane anchors, and disassembly factors are needed to regulate actin ring dynamics spatially and temporally. Notably, Rho family GTPases have been implicated throughout the repair process, whereas other proteins are required during specific phases. Interestingly, although different models share a similar set of recruited proteins, the way in which they use them to pull the wound closed can differ. Here, we describe what is currently known about the formation, translocation, and remodeling of the actin ring during the cell wound repair process in model organisms, as well as the overall impact of cell wound repair on daily events and its importance to our understanding of certain diseases and the development of therapeutic delivery modalities.

This paper presents the development of a metal oxide semiconductor (MOS) sensor for the detection of volatile organic compounds (VOCs) which are of great importance in many applications involving either control of hazardous chemicals or noninvasive diagnosis. In this study, the sensor is fabricated based on tin dioxide (SnO₂) and poly(ethylene oxide) (PEO) using electrospinning. The sensitivity of the proposed sensor is further improved by calcination and gold doping. The gold doping of composite nanofibers is achieved using sputtering, and the calcination is performed using a high-temperature oven. The performance of the sensor with different doping thicknesses and different calcination temperatures is investigated to identify the optimum fabrication parameters resulting in high sensitivity. The optimum calcination temperature and duration are found to be 350 °C and 4 h, respectively and the optimum thickness of the gold dopant is found to be 10 nm. The sensor with the optimum fabrication process is then embedded in a microchannel coated with several metallic and polymeric layers. The performance of the sensor is compared with that of a commercial sensor. The comparison is performed for methanol and a mixture of methanol and tetrahydrocannabinol (THC) which is the primary psychoactive constituent of cannabis. It is shown that the proposed sensor outperforms the commercial sensor when it is embedded inside the channel.

Cells are subjected to a barrage of daily insults that often lead to its cortex being ripped open and requiring immediate repair. An important component of the cell’ s repair response is the formation of an actomyosin ring at the wound periphery to mediate its closure. Inhibition of linear actin nucleation factors and myosin result in a disrupted contractile apparatus and delayed wound closure. Here we show that branched actin nucleators function as a scaffold to assemble and maintain this contractile actomyosin cable. Removing branched actin leads to the formation of smaller circular actin-myosin structures at the cell cortex and slow wound closure. Removing linear and branched actin results in failed wound closure. Surprisingly, removal of branched actin and myosin results in the formation of parallel linear actin filaments that undergo a chiral swirling movement to close the wound. These results provide insight into actin organization in contractile actomyosin rings and uncover a new mechanism of wound closure. Summary Hui et al. find that branched actin is required during cell wound repair to serve as a scaffold to anchor the contractile actomyosin cable at the wound periphery. Inhibition of branched actin and myosin results in parallel linear filaments that swirl to close the wound, uncovering a new mechanism for cell wound repair.

Cell wound repair requires rapid and coordinated remodeling of the actin cytoskeleton to restore cortex integrity. Here, we show that a Rab35-Mical-SelR pathway regulates actomyosin ring dynamics through reversible actin redox. We find that Rab35 is recruited to wounds and is essential for proper actin ring assembly and disassembly. Rab35 regulates the recruitment of Mical, an actin-oxidizing enzyme, and SelR, a reductase that reverses oxidation, to the cell wound. Mical and SelR knockdowns disrupt actin ring formation and wound closure, whereas double knockdown partially rescues these defects, indicating a balanced redox cycle is required. Super-resolution microscopy reveals that Mical and SelR differentially regulate F-actin architecture and orientation. Mutation of actin at Methionine 44 does not fully recapitulate Mical knockdown phenotypes, suggesting the presence of additional targets and enzymes. Taken together, our results indicate that reversible actin modifications dynamically regulate F-actin architecture and orientation for actin ring assembly and disassembly.

The cytokinetic ring (CR) is a vital and dynamic cytoskeletal structure required for precise separation of replicated organelles and chromosomes equally into two daughter cells. Septins are capable of self-assembling into high-order structures, including filaments, rings, gauzes, and collars, and have been demonstrated to act as a scaffold for the assembly of the CR in budding yeast. An important partner of septins is the anillin-like protein, mid2, which has a demonstrated role in bridging septins and the CR. The precise orchestration of these unique cytoskeletal components is fundamental to proper cell division. In this study, the authors use polarized fluorescence microscopy with fission yeast to explore septin filament and mid2 behavior in the cytokinetic ring. Using timelapse microscopy, the authors first established different phases of cytokinesis with respect to Septin 1 (Spn1) fused to GFP. At the onset of CR constriction, Spn1-GFP forms a diffuse ring around the CR, compacts to a dense ring, and eventually splits as the cell divides. They then demonstrated that the fission yeast anillin ortholog (mid2) fused to ENVY (mid2-ENVY) is recruited to the CR later than Spn1 and coincident with the timing of Spn1 compaction. Using timelapse microscopy, the authors found that the septin ring exhibits a considerable decrease in its width in wild-type conditions, but in mid2D cells the septin ring exhibited no change. As the septins formed a diffuse ring in mid2D cells, mid2 is likely acting to compact septin filaments during cytokinesis. The authors then used a series of biochemical assays to show that mid2-mid2 binding is septin-independent and requires its PH domain. As it has been shown previously that mid2DPH does not localize to the CR, the authors fused mid2 to a GFP-binding protein (mid2DPH-GBP) to artificially localize mid2DPH to the CR. Cells expressing mid2DPH-GBP exhibited considerable septin ring compaction, indicating that mid2DPH-GBP can partially rescue the diffuse septin ring phenotype shown in mid2D cells. Interestingly, Spn1 formed clumps at the CR and the septin rings collapsed during CR constriction, indicating that the PH domain in mid2 contributes to septin ring stability. Thus, mid2 likely facilitates septin compaction by bundling and stabilizing septin filaments at the CR. Using a nice combination of timelapse microscopy and polarization-resolved fluorescence microscopy, the authors then investigated possible changes to septin filament orientations. In wild-type conditions, Spn1 filaments were initially randomly oriented and gradually aligned parallel to the CR throughout constriction. Strikingly, in mid2D cells, Spn1 filaments exhibited the opposite phenotype in which they were randomly oriented throughout constriction. These exciting new findings on the role of anillin in septin ring compaction and septin filament orientation bias highlight the intricacies of the CR, as well as the dynamic nature of subcellular structures.