Cytoskeletons (F-actin) and spermatogenesis
C. Yan Cheng in Spermatogenesis, 2018
Actin is one of the most abundant proteins in cells and indeed on Earth.1 The amino acid sequence of actin monomers (also known as globular actin or G-actin) is highly conserved between species. There are three main isoforms of actin monomers, alpha, beta, and gamma, encoded by different genes. Actin monomers are polymerized into filamentous actin (F-actin), which in turn is arranged into higher-order structures via interactions with numerous actin binding and regulatory proteins. Actin participates in many cellular functions, including division, migration, polarity, shape, intercellular adhesion (including cell-cell and cell-substrate adhesion), and intracellular transport. Emerging evidence has revealed actin can also function within the nucleus, regulating gene expression and responding to extracellular cues.2,3
The Aging of the Neuronal Cytoskeleton
Alvaro Macieira-Coelho in Molecular Basis of Aging, 2017
Microfilaments have a diameter of 4 to 6 nm and are composed of actin. As actin is a highly conserved protein, a whole family of actin-associated proteins (AAPs) confers specialized functions to these actin filaments according to the needs of individual cells.1 The 42-kDa actin monomers (G-actin) polymerize into double-helical filaments (F-actin). This polymerization is dependent on ATP hydrolysis. Actin polymerization is a very dynamic process controlled mostly by actin-associated proteins such as profilin (G-actin sequestering) and gelsolin (filament nucleating). Other AAPs such as spectrin and myosin cross-link existing filaments into a network. Ankyrin and spectrin anchor actin filaments to the plasma membrane and to other cellular organelles. Myosin is the motor of cell motility by a sliding filament mechanism. Motility can also appear from transitions between the gel and the sol state of actin filaments interacting with other cytoskeletal filaments and the cell membrane. Through these mechanisms, actin filaments are involved in cell motility, adhesion, membrane stability, determination of cell shape, exocytosis, and cytokinesis.2 Microfilaments, therefore, act simultaneously as the cell “skeleton and muscles”.
Evaluating the Interactions of Silver Nanoparticles and Mammalian Cells Based on Biomics Technologies
Huiliang Cao in Silver Nanoparticles for Antibacterial Devices, 2017
Actin cytoskeleton plays its role in the conservation of cell morphology and polarity, endocytosis, intracellular trafficking, contractility, motility and cell division (Gourlay and Ayscough 2005). In Figure 10.4, 12 differentially expressed genes were found included in the ‘regulation of actin cytoskeleton pathway’, with 6 genes up-regulated and 6 genes down-regulated. Up-regulated ARPC5 is very important for the organisation of the Arp2/3 protein complex, which is related to the control of actin polymerisation. Actin polymerisation can be regulated by external stimuli and plays the main role in many physiological functions, particularly in cell motility (Mitchison and Cramer 1996). Thus, the up-regulation of ARPC5 might imply the abnormality of actin polymerisation. Gourlay et al. reported that actin cytoskeleton could regulate ROS release from mitochondria and played a key role in activating cell death pathways. The supposed mechanism is that actin can master the opening and closing of the voltage-dependent anion channel on the mitochondria outer membrane and then control the release of apoptogenic proteins, including cytochrome c (Gourlay and Ayscough 2005).
Myosin light chain kinase regulates intestinal permeability of mucosal homeostasis in Crohn’s disease
Published in Expert Review of Clinical Immunology, 2020
Many studies have demonstrated how MLCK directly regulates the ability of the cytoskeleton to activate the TJ barrier [48,53,54]. Ca2+/calmodulin-dependent MLCK phosphorylates the myosin RLC and activates myosin in the smooth muscle. Then, ATPase in the myosin head is activated to hydrolyze ATP, thereby converting the chemical energy to mechanical forces and motion [55]. At the same time, actin assembles to form actin filaments. Then, the heavy chain motor domain of myosin reversibly binds to actin filaments, leading to cyclic interaction between actin and myosin. With hydrolyzation of ATP (the basis of energy) and assembly of actin (the basis of structure), interaction between MLCK and skeletal proteins contributes to the interplay and contraction of skeletal proteins, finally leading to contraction of the intestinal cells [39]. With contraction of the cytoskeleton, the paracellular pathways sealed by the TJ are activated to increase intestinal permeability. Additionally, Rho-associated kinase (ROCK) has a similar role in myosin phosphorylation and activation [56].
Epithelial maturity influences EPEC-induced desmosomal alterations
Published in Gut Microbes, 2019
Jennifer Lising Roxas, Gayatri Vedantam, V.K. Viswanathan
While the exact mechanism by which Rho inactivation leads to desmosomal perturbations remains to be defined, our studies suggest an intersecting role for Rho-mediated modulation of actin in the maintenance of keratin IFs and in the transport of component proteins to the desmosomal plaques. In the prevailing model for IF assembly, the transport of cytokeratin precursors to the periphery, bundling, and maturation towards the cell center is dependent on actin retrograde flow.20,21 Actin cytoskeleton dynamics are controlled by a balance of actin polymerization and depolymerization. Rho activation is known to promote actin polymerization. Consistent with a role for Rho-mediated actin polymerization in the maintenance of keratin IFs in intestinal epithelial cells, we observed that the actin-stabilizing compound jasplakinolide rescues infected cells from EPEC-induced keratin retraction.16
Copper oxide nanoparticles alter cellular morphology via disturbing the actin cytoskeleton dynamics in Arabidopsis roots
Published in Nanotoxicology, 2020
Honglei Jia, Sisi Chen, Xiaofeng Wang, Cong Shi, Kena Liu, Shuangxi Zhang, Jisheng Li
Actin was extracted from rabbit muscle and used to test the effect of CuO NPs on actin dynamics. Nucleation is the limiting step of actin polymerization. The effect of CuO NPs on actin polymerization was represented by the nucleation rate in vitro. As shown in Figure 7(a), the actin polymerization kinetics were monitored by pyrene fluorescence; the initial lag that corresponds to the nucleation step decreased with increasing concentration of CuO NPs, and this decrease occurred in a dose-dependent manner. To determine whether CuO NPs affected the stability of F-actin in vitro, a dilution-mediated actin depolymerization assay was performed. As shown in Figure 7(b), CuO NP treatment enhanced the rate of depolymerization in a concentration-dependent manner. In addition, Cu2+ treatment did not affect the polymerization of actin monomers or the depolymerization of F-actin (Figure 7(a,b)). The formation of the F-actin bundle was visualized by fluorescence microscopy in vitro. Long and thick F-actin bundles were observed in the control. In contrast, a smaller amount of F-actin and short F-actin bundles were observed with increasing concentrations of CuO NPs (Figure 7(c,d)).
Related Knowledge Centers
- Cytoskeleton
- Eukaryote
- Globular Protein
- Microfilament
- Monomer
- Muscle Contraction
- Myofibril
- Protein
- Protein Subunit
- Protein Family