Structural insight eludes on how full-length gelsolin depolymerizes and caps filamentous (F-)actin, while the same entity can nucleate polymerization of G-actins. Analyzing small angle X-ray scattering (SAXS) data, we deciphered assemblies which enable these contrasting processes. Mixing Ca2+-gelsolin with F-actin in high salt F-buffer resulted in depolymerization of ordered F-actin rods to smaller sized species which became monodispersed upon dialysis with low salt G-buffer. These entities were the ternary (GA2) and binary (GA) complexes of gelsolin and actin with radius of gyration and maximum linear dimension of 4.55 and 4.68 nm, and 15 and 16 nm, respectively. Using size exclusion chromatography in-line with SAXS, we confirmed that initially GA and GA2 species are formed as seen upon depolymerization of F-actin followed by dialysis. Interestingly, while GA2 could seed formation of native-like F-actin in both G- and F-buffer, GA failed in G-buffer. Thus, GA2 and GA are the central species formed via depolymerization or towards nucleation. SAXS profile referenced modeling revealed that: 1) in GA, actin is bound to the C-terminal half of gelsolin, and 2) in GA2, second actin binds to the open N-terminal half accompanied by dramatic rearrangements across g1-g2 and g3-g4 linkers.

The actin cytoskeleton is involved in a large number of cellular signaling events in addition to providing structural integrity to the cell. Actin polymerization is a key event during cellular signaling. Although the role of actin cytoskeleton in cellular processes such as trafficking and motility has been extensively studied, the reorganization of the actin cytoskeleton upon signaling has been rarely explored due to lack of suitable assays. Keeping in mind this lacuna, we developed a confocal microscopy based approach that relies on high magnification imaging of cellular F-actin, followed by image reconstruction using commercially available software. In this review, we discuss the context and relevance of actin quantitation, followed by a detailed hands-on approach of the methodology involved with specific points on troubleshooting and useful precautions. In the latter part of the review, we elucidate the method by discussing applications of actin quantitation from our work in several important problems in contemporary membrane biology ranging from pathogen entry into host cells, to GPCR signaling and membrane-cytoskeleton interaction. We envision that future discovery of cell-permeable novel fluorescent probes, in combination with genetically encoded actin-binding reporters, would allow real-time visualization of actin cytoskeleton dynamics to gain deeper insights into active cellular processes in health and disease.

Gellan gum (GG) is a soft, tractable,　and natural polysaccharide substrate used for cell incubation. In this study, we examined the effects of GG on porcine oocyte maturation. Cumulus cells and oocyte complexes (COCs) were collected from slaughterhouse-derived porcine ovaries and cultured on plastic plates containing 0.05% or 0.1% GG gels. The 0.1% GG gel improved the maturation rate and quality of blastocysts, as determined by the total cell number and the rate of abnormally condensed nuclei. GG gels have antioxidant abilities and oocytes cultured on GG gels (0.05% and 0.1%) have reduced reactive oxygen species (ROS) content. Furthermore, GG gels (0.05% and 0.1%) increased F-actin formation, whereas treatment of oocytes with H2O2 reduced F-actin levels. GG gels increased the ATP content in oocytes but did not affect the mitochondrial DNA copy number or mitochondrial membrane potential. In addition, the medium cultured on 0.05% GG increased the glucose consumption of COCs. In conclusion, GG gel reduced ROS content, increased energy content, and improved subsequent embryonic development in pigs.

The reorganization of the cell cytoskeleton and changes in the content of cell adhesion molecules are crucial during the metastatic spread of tumor cells. Colorectal cancer (CRC) cells express high SMAD7, a protein involved in the control of CRC cell growth. In the present study, we evaluated whether SMAD7 regulates the cytoskeleton reorganization and dynamics in CRC. Knockdown of SMAD7 with a specific antisense oligonucleotide (AS) in HCT116 and DLD1, two human CRC cell lines, reduced the migration rate and the content of F-ACTIN filaments. A gene array, real-time PCR, and Western blotting of SMAD7 AS-treated cells showed a marked down-regulation of the X-linked inhibitor of apoptosis protein (XIAP), a member of the inhibitor of apoptosis family, which has been implicated in cancer cell migration. IL-6 and IL-22, two cytokines that activate STAT3, enhanced XIAP in cancer cells, and such induction was attenuated in SMAD7-deficient cells. Finally, in human CRC, SMAD7 mRNA correlated with XIAP expression. Our data show that SMAD7 positively regulates XIAP expression and migration of CRC cells, and suggest a mechanism by which SMAD7 controls the architecture components of the CRC cell cytoskeleton.

Mechanical properties, along with biochemical and molecular properties, play crucial roles in governing cellular function and homeostasis. Cellular mechanics are influenced by various factors, including physiological and pathological states, making them potential biomarkers for diseases and aging. While several methods such as AFM, particle-tracking microrheology, optical tweezers/stretching, magnetic tweezers/twisting cytometry, microfluidics, and micropipette aspiration have been widely utilized to measure the mechanical properties of single cells, our understanding of how aging affects these properties remains limited. To fill this knowledge gap, we provide a brief overview of the commonly used methods to measure single-cell mechanical properties. We then delve into the effects of aging on the mechanical properties of different cell types. Finally, we discuss the importance of studying cellular viscous and viscoelastic properties as well as aging induced by different stressors to gain a deeper understanding of the aging process and aging-related diseases.

Plasma membrane repair is a fundamental homeostatic process of eukaryotic cells. Here, we report a new function for the conserved cytoskeletal proteins known as septins in the repair of cells perforated by pore-forming toxins or mechanical disruption. Using a silencing RNA screen, we identified known repair factors (e.g. annexin A2, ANXA2) and novel factors such as septin 7 (SEPT7) that is essential for septin assembly. Upon plasma membrane injury, the septin cytoskeleton is extensively redistributed to form submembranous domains arranged as knob and loop structures containing F-actin, myosin IIA, S100A11, and ANXA2. Formation of these domains is Ca2+-dependent and correlates with plasma membrane repair efficiency. Super-resolution microscopy revealed that septins and F-actin form intertwined filaments associated with ANXA2. Depletion of SEPT7 prevented ANXA2 recruitment and formation of submembranous actomyosin domains. However, ANXA2 depletion had no effect on domain formation. Collectively, our data support a novel septin-based mechanism for resealing damaged cells, in which the septin cytoskeleton plays a key structural role in remodeling the plasma membrane by promoting the formation of SEPT/F-actin/myosin IIA/ANXA2/S100A11 repair domains.

In most mollusks (conchiferans), the early tissue responsible for shell development, namely, the shell field, shows a common process of invagination during morphogenesis. Moreover, lines of evidence indicated that shell field invagination is not an independent event, but an integrated output reflecting the overall state of shell field morphogenesis. Nevertheless, the underlying mechanisms of this conserved process remain largely unknown. We previously found that actomyosin networks (regularly organized filamentous actin (F-actin) and myosin) may play essential roles in this process by revealing the evident aggregation of F-actin in the invaginated region and demonstrating that nonmuscle myosin II (NM II) is required for invagination in the gastropod Lottia peitaihoensis (= Lottia goshimai). Here, we investigated the roles of the Rho family of small GTPases (RhoA, Rac1, and Cdc42) to explore the upstream regulators of actomyosin networks. Functional assays using small molecule inhibitors suggested that Cdc42 modulates key events of shell field morphogenesis, including invagination and cell rearrangements, while the roles of RhoA and Rac1 may be nonspecific or negligible. Further investigations revealed that the Cdc42 protein was concentrated on the apical side of shell field cells and colocalized with F-actin aggregation. The aggregation of these two molecules could be prevented by treatment with Cdc42 inhibitors. These findings suggest a possible regulatory cascade of shell field morphogenesis in which Cdc42 recruits F-actin (actomyosin networks) on the apical side of shell field cells, which then generates resultant mechanical forces that mediate correct shell field morphogenesis (cell shape changes, invagination and cell rearrangement). Our results emphasize the roles of the cytoskeleton in early shell development and provide new insights into molluscan shell evolution.

Sirtuin 5 (Sirt5), a member of the Sirtuin family, is involved in various intracellular biological processes. However, the function of Sirt5 in oocyte maturation has not been clearly elucidated. In this study, we observed that Sirt5 was persistently expressed during the meiotic division of mouse oocytes, with a notable decline in expression in aging oocytes. Sirt5 inhibition led to the failure of the first polar body extrusion and induced cell cycle arrest, indicative of unsuccessful oocyte maturation. Furthermore, Sirt5 inhibition was associated with the extrusion of abnormally large polar bodies, suggesting disrupted asymmetric oocyte division. Mechanistically, the inhibition of Sirt5 resulted in aberrant spindle assembly and disordered chromosome alignment in oocytes. Moreover, Sirt5 inhibition caused the spindle to be centrally located in the oocyte without migrating to the cortical region, consequently preventing the formation of the actin cap. Further investigation revealed that Sirt5 inhibition notably diminished the expression of phosphorylated cofilin and profilin1, while increasing cytoplasmic F-actin levels. These findings suggest that Sirt5 inhibition during oocyte maturation adversely affects spindle assembly and chromosome alignment and disrupts actin dynamics impairing spindle migration and contributing to the failure of symmetric oocyte division and maturation.

Colorectal cancer (CRC) is significantly contributed to global cancer mortality rates. Treating CRC is particularly challenging due to metastasis and drug resistance. There is a pressing need for new treatment strategies against metastatic CRC. Photodynamic therapy (PDT) offers a well-established, minimally invasive treatment option for cancer with limited side effects. Hypericin (HYP), a potent photosensitizer for PDT, has been documented to induce cytotoxicity and apoptosis in various types of cancers. However, there are few reports on the inhibitory effects of HYP-mediated PDT on the metastatic ability of CRC cells. Here, we evaluate the inhibitory effects of HYP-mediated PDT against metastatic CRC cells and define its underlying mechanisms. Wound-healing and Transwell assays show that HYP-mediated PDT suppresses migration and invasion of CRC cells. F-actin visualization assays indicate HYP-mediated PDT decreases F-actin formation in CRC cells. TEM assays reveal HYP-mediated PDT disrupts pseudopodia formation of CRC cells. Mechanistically, immunofluorescence and western blotting results show that HYP-mediated PDT upregulates E-cadherin and downregulates N-cadherin and Vimentin. HYP-mediated PDT also suppresses key EMT regulators, including Snail, MMP9, ZEB1 and α-SMA. Additionally, the expressions of RhoA and ROCK1 are downregulated by HYP-mediated PDT. Together, these findings suggest that HYP-mediated PDT inhibits the migration and invasion of HCT116 and SW620 cells by modulating EMT and RhoA-ROCK1 signaling pathway. Thus, HYP-mediated PDT presents a potential therapeutic option for CRC.

Background Hailey-Hailey disease (HHD) is a rare, autosomal dominant, hereditary skin disorder characterised by epidermal acantholysis. The HHD-associated gene ATPase calcium-transporting type 2C member 1 (ATP2C1) encodes the protein secretory pathway Ca2+ ATPase1 (SPCA1), playing a critical role in HHD pathogenesis. Aims We aimed to investigate the effect of ATP2C1 knockdown on keratinocytes that mimicked acantholysis in HHD. Methods Immunohistochemistry (IHC) was employed to evaluate the levels of cytoskeletal and tight junction proteins such as SPCA1, P-cofilin, F-actin, claudins, occludin, and zonula occludens 1 in the skin biopsies of patients with HHD. Subsequently, the expression of these proteins in cultured ATP2C1 knockdown keratinocytes was analysed using Western blotting and immunofluorescence. Furthermore, we assessed the proliferation, apoptosis, and intracellular Ca2+ concentrations in the ATP2C1-knocked keratinocytes. Results The results showed decreased levels of these proteins (SPCA1, P-cofilin, F-actin, claudins, occluding, and zonula occludens 1) in HHD skin lesions. Moreover, their levels decreased in human keratinocytes transfected with ATP2C1 short hairpin RNA, accompanied by morphological acantholysis. Furthermore, the proliferation and apoptosis of the keratinocytes, as well as intracellular calcium concentrations in these cells, were not affected. Limitations The limitations of this study are the absence of animal experiments and the failure to explore the relationship between skeletal and tight junction proteins. Conclusion The present study indicated that ATP2C1 inhibition led to abnormal levels of the cytoskeletal and tight junction proteins in the keratinocytes. Therefore, keratinocytes can mimic HHD-like acantholysis and serve as an in vitro model, helping develop treatment strategies against HHD.