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The Scientific Basis of Medicine
Published in John S. Axford, Chris A. O'Callaghan, Medicine for Finals and Beyond, 2023
Chris O'Callaghan, Rachel Allen
The fluid nature of the outer phospholipid membrane that surrounds the cell allows proteins to move around its surface. The cytosol is the site of many cellular reactions and contains all the necessary machinery for protein synthesis. A cytoskeleton of microfilaments, intermediate filaments and microtubules provides physical support for the various organelles and forms transport routes between them.
Phagocytosis By Human Neutrophils
Published in Hans H. Gadebusch, Phagocytes and Cellular Immunity, 2020
The microfilaments are apparently composed of contractile proteins. Actin, myosin, and an actin-binding protein have been partially purified from both neutrophils7*'81 and macrophages.82,83 The phagocytic myosin has Mg2+-ATPase activity that is increased markedly in the presence of actin;79,80 in the case of macrophages, an additional cofactor is required for this activation.81 It appears as though the actin in leukocytes is capable of a reversible polymerization, resulting in a reversible gelation phenomenon in vitro;79 electron micrographs show the formation of a tangled filamentous network when actin, myosin, and actin-binding protein are mixed in vitro.79-81 The most important direct evidence for the significance of this system to leukocyte mobility lies in the identification of a patient with inadequate ability to polymerize actin.*4 This child was originally observed to have recurrent bacterial infections but minimal signs of inflammation. Studies of cell mobility both in vivo and in vitro showed poor migration and particle ingestion was abnormal. Although the total cellular actin content was normal, it did not polymerize to the usual extent under a normal stimulus (addition of KC1). Thus it appears as though defective actin polymerization leads to a functional defect in cellular locomotion.
Structural Organization of the Liver
Published in Robert G. Meeks, Steadman D. Harrison, Richard J. Bull, Hepatotoxicology, 2020
Actin filaments (microfilaments) are the polymerized form of actin (F actin or fibrous actin) which measures 6 nm in diameter. They are formed from a pool of soluble subunits, G (globular) actin, and disassembled when no longer needed. This balance between assembly and disassembly is disturbed by specific chemicals that inhibit or enhance polymerization and lead to abnormal accumulation of either the polymer filaments or depolymerized subunits. Cytochalasins inhibit polymerization while phalloidin enhances it (Alberts et al., 1983).
Graphene 2D platform is safe and cytocompatibile for HaCaT cells growing under static and dynamic conditions
Published in Nanotoxicology, 2022
Iwona Lasocka, Elzbieta Jastrzębska, Agnieszka Zuchowska, Ewa Skibniewska, M. Skibniewski, Lidia Szulc-Dąbrowska, Iwona Pasternak, Jakub Sitek, Marie Hubalek Kalbacova
Cell membrane is also crucial for cell adhesion, because it contains receptors (integrins) that act as sensors of external signals, allowing the cell to respond to environmental cues (Lotfi, Nejib, and Naceur 2013). Integrins (signaling layer of focal adhesion) transmit information to the force transduction layer (vinculin, talin) and further to actin regulatory layer connected to actin stress fibers (actin cytoskeleton). Focal adhesion kinase (FAK) is today recognized as a hub in the interactome of focal adhesions (Martínez, Navajas, and Lietha 2020), thus its visualization could help to reveal the interaction between cells and graphene substrate. As shown in Figure 7, adhesion sites based on FAK and F-actin colocalization are already visible at the third hour of incubation on the graphene covered coverslips (Figure 7(A)) and control coverslips (Figure 7(B)). The cells are spherical in shape and begin to form clusters, but most of them are still single cells. After next 21 hours, the adhesion sites become more pronounced and cells stick tightly to each other and become more spread in clusters consisting of four to six cells (Figure 7(C)). There is a clearly visible „FAK frame” around the cell cluster that colocalizes with actin filaments and organized microfilaments are evenly distributed in the cytoplasm (Figure 7(C)). No more organized structures like microfilament bundles or stress fibers were observed in these cells cultivated on neither substrate.
Heterogeneous Differentiation of Highly Proliferative Embryonal Carcinoma PCC4 Cells Induced by Curcumin: An In Vitro Study
Published in Nutrition and Cancer, 2021
Geetha Viswanathan, Lip Yong Chung, Usha K. Srinivas
Since we observed an enhanced formation of focal adhesions in the differentiated PCC4 cells, there could also be changes in cell motility because these two processes are connected. Lamellipodia and stress bundles are two important organized structures composed of microfilaments that form during cell migration. Actin stress bundles were observed in the differentiated cells (Figure 1B). Manual tracking of the migration paths of individual cells clearly demonstrated that the motility of PCC4 cells gradually increased during curcumin treatment (P < 0.05), reaching a maximum speed after 48 h of treatment (Figure 5C). The track overlays depicted in Figure 5D illustrated the differences between the motility of the untreated control and the curcumin-treated cells at 48 h, and they clearly showed that individual curcumin-treated differentiated cells had longer track overlays compared to the control cells.
TiO2 nanotubes regulate histone acetylation through F-actin to induce the osteogenic differentiation of BMSCs
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2021
Yanchang Liu, Zhicheng Tong, Chen Wang, Runzhi Xia, Huiwu Li, Haoran Yu, Juehua Jing, Wendan Cheng
Cytoskeleton is a kind of cell scaffold in cytoplasm. It maintains cell shape, provides mechanical strength, directs movement, regulates chromosome segregation during mitosis and meiosis, and intracellular organelle transport [10,11]. Actin microfilament is the main structure of cytoskeleton. Actin exists in cells in the form of globular/monomer actin (G-actin) or fibrous actin (F-actin), in which the F-actin is the main part of the cytoskeleton, which can quickly aggregate and depolymerize and is directly related to the adhesion, extension and migration of cells. F-actin provides mechanical support for cells, influences the tension in the cytoskeleton, and provides pathways through the cytoplasm to help signal transduction [12,13]. F-actin has been shown to induce lipid differentiation in cultured BMSCs [14]. The role of actin dynamics in the differentiation of chondrocytes from BMSCs has also been supported by numerous experiments. F-actin interfering compounds, such as Cytochalasin D, can induce cartilage differentiation [15]. Previous studies have found that F-actin in the cytoskeleton is very sensitive to external mechanical and physical signal stimulation. On the metal surface, the aggregation of F-actin is more obvious, forming a stronger cytoskeleton. On the surface of the hydrogel, the polymerization of F-actin is weakened. And the change of cytoskeleton is accompanied by the change of cell morphology and the expression of differentiation-related markers [16]. Therefore, F-actin itself can be used as a bridge for mechanical signals to regulate cell biological behaviour.