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ELife Nov 2023The MRTF-SRF pathway has been extensively studied for its crucial role in driving the expression of a large number of genes involved in actin cytoskeleton of various...
The MRTF-SRF pathway has been extensively studied for its crucial role in driving the expression of a large number of genes involved in actin cytoskeleton of various cell types. However, the specific contribution of MRTF-SRF in hair cells remains unknown. In this study, we showed that hair cell-specific deletion of or , but not a, leads to similar defects in the development of stereocilia dimensions and the maintenance of cuticular plate integrity. We used fluorescence-activated cell sorting-based hair cell RNA-Seq analysis to investigate the mechanistic underpinnings of the changes observed in and mutants, respectively. Interestingly, the transcriptome analysis revealed distinct profiles of genes regulated by and , suggesting different transcriptional regulation mechanisms of actin cytoskeleton activities mediated by and . Exogenous delivery of calponin 2 using Adeno-associated virus transduction in mutants partially rescued the impairments of stereocilia dimensions and the F-actin intensity of cuticular plate, suggesting the involvement of , as an downstream target, in regulating the hair bundle morphology and cuticular plate actin cytoskeleton organization. Our study uncovers, for the first time, the unexpected differential transcriptional regulation of actin cytoskeleton mediated by and in hair cells, and also demonstrates the critical role of SRF-CNN2 in modulating actin dynamics of the stereocilia and cuticular plate, providing new insights into the molecular mechanism underlying hair cell development and maintenance.
Topics: Hair Cells, Auditory; Actin Cytoskeleton; Stereocilia; Actins; Gene Expression Regulation
PubMed: 37982489
DOI: 10.7554/eLife.90155 -
European Journal of Cell Biology 2022Actin is among the most abundant proteins in eukaryotic cells and assembles into dynamic filamentous networks regulated by many actin binding proteins. The actin... (Review)
Review
Actin is among the most abundant proteins in eukaryotic cells and assembles into dynamic filamentous networks regulated by many actin binding proteins. The actin cytoskeleton must be finely tuned, both in space and time, to fulfill key cellular functions such as cell division, cell shape changes, phagocytosis and cell migration. While actin oxidation by reactive oxygen species (ROS) at non-physiological levels are known for long to impact on actin polymerization and on the cellular actin cytoskeleton, growing evidence shows that direct and reversible oxidation/reduction of specific actin amino acids plays an important and physiological role in regulating the actin cytoskeleton. In this review, we describe which actin amino acid residues can be selectively oxidized and reduced in many different ways (e.g. disulfide bond formation, glutathionylation, carbonylation, nitration, nitrosylation and other oxidations), the cellular enzymes at the origin of these post-translational modifications, and the impact of actin redox modifications both in vitro and in vivo. We show that the regulated balance of oxidation and reduction of key actin amino acid residues contributes to the control of actin filament polymerization and disassembly at the subcellular scale and highlight how improper redox modifications of actin can lead to pathological conditions.
Topics: Actin Cytoskeleton; Actins; Amino Acids; Microfilament Proteins; Oxidation-Reduction
PubMed: 35716426
DOI: 10.1016/j.ejcb.2022.151249 -
PLoS Computational Biology Jul 2022Cadherins build up clusters to maintain intercellular contact through trans and cis (lateral) bindings. Meanwhile, interactions between cadherin and the actin...
Cadherins build up clusters to maintain intercellular contact through trans and cis (lateral) bindings. Meanwhile, interactions between cadherin and the actin cytoskeleton through cadherin/F-actin linkers can affect cadherin dynamics by corralling and tethering cadherin molecules locally. Despite many experimental studies, a quantitative, mechanistic understanding of how cadherin and actin cytoskeleton interactions regulate cadherin clustering does not exist. To address this gap in knowledge, we developed a coarse-grained computational model of cadherin dynamics and their interaction with the actin cortex underlying the cell membrane. Our simulation predictions suggest that weak cis binding affinity between cadherin molecules can facilitate large cluster formation. We also found that cadherin movement inhibition by actin corralling is dependent on the concentration and length of actin filaments. This results in changes in cadherin clustering behaviors, as reflected by differences in cluster size and distribution as well as cadherin monomer trajectory. Strong cadherin/actin binding can enhance trans and cis interactions as well as cadherin clustering. By contrast, with weak cadherin/actin binding affinity, a competition between cadherin-actin binding and cis binding for a limited cadherin pool leads to temporary and unstable cadherin clusters.
Topics: Actin Cytoskeleton; Actins; Cadherins; Cell Adhesion; Cell Membrane; Cluster Analysis
PubMed: 35802763
DOI: 10.1371/journal.pcbi.1010257 -
ELife Jul 2022Experiments using purified proteins reveal how the network of filaments that underlie cell movement becomes denser when pushing against a stronger mechanical force.
Experiments using purified proteins reveal how the network of filaments that underlie cell movement becomes denser when pushing against a stronger mechanical force.
Topics: Actin Cytoskeleton; Actin-Related Protein 2-3 Complex; Actins; Cell Movement; Cytoskeleton
PubMed: 35894589
DOI: 10.7554/eLife.81108 -
Trends in Cell Biology Mar 2023Detection and conversion of mechanical forces into biochemical signals is known as mechanotransduction. From cells to tissues, mechanotransduction regulates migration,... (Review)
Review
Detection and conversion of mechanical forces into biochemical signals is known as mechanotransduction. From cells to tissues, mechanotransduction regulates migration, proliferation, and differentiation in processes such as immune responses, development, and cancer progression. Mechanosensitive structures such as integrin adhesions, the actin cortex, ion channels, caveolae, and the nucleus sense and transmit forces. In vitro approaches showed that mechanosensing is based on force-dependent protein deformations and reorganizations. However, the mechanisms in cells remained unclear since cell imaging techniques lacked molecular resolution. Thanks to recent developments in super-resolution microscopy (SRM) and molecular force sensors, it is possible to obtain molecular insight of mechanosensing in live cells. We discuss how understanding of molecular mechanotransduction was revolutionized by these innovative approaches, focusing on integrin adhesions, actin structures, and the plasma membrane.
Topics: Humans; Mechanotransduction, Cellular; Actins; Cytoskeleton; Integrins; Microscopy; Cell Adhesion; Actin Cytoskeleton
PubMed: 36055943
DOI: 10.1016/j.tcb.2022.07.008 -
Communications Biology Sep 2023Actin, an important component of eukaryotic cell cytoskeleton, regulates cell shape and transport. The morphology and biochemical properties of actin filaments are...
Actin, an important component of eukaryotic cell cytoskeleton, regulates cell shape and transport. The morphology and biochemical properties of actin filaments are determined by their structure and protein-protein contacts. Crowded environments can organize filaments into bundles, but less is known about how they affect F-actin structure. This study used 2D IR spectroscopy and spectral calculations to examine how crowding and bundling impact the secondary structure and local environments in filaments and weakly or strongly bundled networks. The results reveal that bundling induces changes in actin's secondary structure, leading to a decrease in β-sheet and an increase in loop conformations. Strongly bundled networks exhibit a decrease in backbone solvent exposure, with less perturbed α-helices and nearly "locked" β-sheets. Similarly, the loops become less hydrated but maintain a dynamic environment. These findings highlight the role of loop structure in actin network morphology and stability under morphology control by PEG.
Topics: Actins; Actin Cytoskeleton; Protein Structure, Secondary; Cytoskeleton; Cell Shape
PubMed: 37660224
DOI: 10.1038/s42003-023-05274-3 -
Nucleus (Austin, Tex.) Dec 2024The view on nuclear filaments formed by non-skeletal β-actin has significantly changed over the decades. Initially, filamentous actin was observed in amphibian oocyte... (Review)
Review
The view on nuclear filaments formed by non-skeletal β-actin has significantly changed over the decades. Initially, filamentous actin was observed in amphibian oocyte nuclei and only under specific cell stress conditions in mammalian cell nuclei. Improved labeling and imaging technologies have permitted insights into a transient but microscopically apparent filament network that is relevant for chromatin organization, biomechanics of the mammalian cell nucleus, gene expression, and DNA damage repair. Here, we will provide a historical perspective on the developing insight into nuclear actin filaments.
Topics: Animals; Cell Nucleus; Actin Cytoskeleton; Actins; Cytoskeleton; Oocytes; Mammals
PubMed: 38384139
DOI: 10.1080/19491034.2024.2320656 -
Scientific Reports Jul 2020S100A6 is a low molecular weight Ca-binding protein belonging to the S100 family. Many reports indicate that in the cell S100A6 has an influence on the organization of...
S100A6 is a low molecular weight Ca-binding protein belonging to the S100 family. Many reports indicate that in the cell S100A6 has an influence on the organization of actin filaments, but so far no direct interaction between S100A6 and actin has been shown. In the present study we investigated binding of S100A6 to actin and the actin-tropomyosin complex. The analyses were performed on G- and F-actin and two tropomyosin isoforms-Tpm1.6 and Tpm1.8. Using purified proteins and a variety of biochemical approaches we have shown that, in a Ca-bound form, S100A6 directly interacts with G- and F-actin and with tropomyosin, preferentially with isoform Tpm1.8. S100A6 and tropomyosin bind to the same population of filaments and the presence of tropomyosin on the microfilament facilitates the binding of S100A6. By applying proximity ligation assay we have found that in NIH3T3 fibroblasts S100A6 forms complexes both with actin and with tropomyosin. These results indicate that S100A6, through direct interactions with actin and tropomyosin, might regulate the organization and functional properties of microfilaments.
Topics: Actin Cytoskeleton; Actins; Animals; Mice; NIH 3T3 Cells; Protein Binding; Protein Isoforms; S100 Calcium Binding Protein A6; Tropomyosin
PubMed: 32733033
DOI: 10.1038/s41598-020-69752-y -
International Journal of Molecular... Oct 2022The actin cytoskeleton lies at the heart of many essential cellular processes. There are hundreds of proteins that cells use to control the size and shape of actin... (Review)
Review
The actin cytoskeleton lies at the heart of many essential cellular processes. There are hundreds of proteins that cells use to control the size and shape of actin cytoskeletal networks. As such, various pathogens utilize different strategies to hijack the infected eukaryotic host actin dynamics for their benefit. These include the control of upstream signaling pathways that lead to actin assembly, control of eukaryotic actin assembly factors, encoding toxins that distort regular actin dynamics, or by encoding effectors that directly interact with and assemble actin filaments. The latter class of effectors is unique in that, quite often, they assemble actin in a straightforward manner using novel sequences, folds, and molecular mechanisms. The study of these mechanisms promises to provide major insights into the fundamental determinants of actin assembly, as well as a deeper understanding of host-pathogen interactions in general, and contribute to therapeutic development efforts targeting their respective pathogens. This review discusses mechanisms and highlights shared and unique features of actin assembly by pathogen effectors that directly bind and assemble actin, focusing on eukaryotic actin nucleator functional mimics Sca2 (formin mimic), BimA (Ena/VASP mimic), and VopL (tandem WH2-motif mimic).
Topics: Actin Cytoskeleton; Actins; Eukaryota; Eukaryotic Cells; Formins
PubMed: 36232907
DOI: 10.3390/ijms231911606 -
Annual Review of Cell and Developmental... Oct 2020Many fundamental cellular processes such as division, polarization, endocytosis, and motility require the assembly, maintenance, and disassembly of filamentous actin... (Review)
Review
Many fundamental cellular processes such as division, polarization, endocytosis, and motility require the assembly, maintenance, and disassembly of filamentous actin (F-actin) networks at specific locations and times within the cell. The particular function of each network is governed by F-actin organization, size, and density as well as by its dynamics. The distinct characteristics of different F-actin networks are determined through the coordinated actions of specific sets of actin-binding proteins (ABPs). Furthermore, a cell typically assembles and uses multiple F-actin networks simultaneously within a common cytoplasm, so these networks must self-organize from a common pool of shared globular actin (G-actin) monomers and overlapping sets of ABPs. Recent advances in multicolor imaging and analysis of ABPs and their associated F-actin networks in cells, as well as the development of sophisticated in vitro reconstitutions of networks with ensembles of ABPs, have allowed the field to start uncovering the underlying principles by which cells self-organize diverse F-actin networks to execute basic cellular functions.
Topics: Actin Cytoskeleton; Actins; Animals; Humans; Microfilament Proteins; Models, Biological; Schizosaccharomyces
PubMed: 33021819
DOI: 10.1146/annurev-cellbio-032320-094706