Search PubMed⌕ Search

PubMed · 11948613

Bacterial actins? An evolutionary perspective.

Abstract

According to the conventional wisdom, the existence of a cytoskeleton in eukaryotes and its absence in prokaryotes constitute a fundamental divide between the two domains of life. An integral part of the dogma is that a cytoskeleton enabled an early eukaryote to feed upon prokaryotes, a consequence of which was the occasional endosymbiosis and the eventual evolution of organelles. Two recent papers1, 2 present compelling evidence that actin, one of the principal components of a cytoskeleton, has a homolog in Bacteria that behaves in many ways like eukaryotic actin. Sequence comparisons reveal that eukaryotic actin and the bacterialhomolog (mreB protein), unlike many other proteins common to eukaryotes and Bacteria, have very different and more highly extended evolutionary histories.

Explore related subjects

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Russell F Doolittle, Amanda L York. 2002. Bacterial actins? An evolutionary perspective.. https://doi.org/10.1002/bies.10079

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

Nap1-mediated actin remodeling is essential for mammalian myoblast fusion.

Myoblast fusion is crucial for the formation, growth, maintenance and regeneration of healthy skeletal muscle. Unfortunately, the molecular machinery, cell behaviors, and membrane and cytoskeletal remodeling events that govern fusion and myofiber formation remain poorly understood. Using time-lapse imaging approaches on mouse C2C12 myoblasts, we identify discrete and specific molecular events at myoblast membranes during fusion and myotube formation. These events include rearrangement of cell shape from fibroblast to spindle-like morphologies, changes in lamellipodial and filopodial extensions during different periods of differentiation, and changes in membrane alignment and organization during fusion. We find that actin-cytoskeleton remodeling is crucial for these events: pharmacological inhibition of F-actin polymerization leads to decreased lamellipodial and filopodial extensions and to reduced myoblast fusion. Additionally, shRNA-mediated inhibition of Nap1, a member of the WAVE actin-remodeling complex, results in accumulations of F-actin structures at the plasma membrane that are concomitant with a decrease in myoblast fusion. Our data highlight distinct and essential roles for actin cytoskeleton remodeling during mammalian myoblast fusion, provide a platform for cellular and molecular dissection of the fusion process, and suggest a functional conservation of Nap1-regulated actin-cytoskeleton remodeling during myoblast fusion between mammals and Drosophila.

Actins↗

Expression of NGF in hepatocellular carcinoma cells with its receptors in non-tumor cell components.

Nerve growth factor (NGF) is suggested to have a role in tumor progression in addition to its role in differentiation and survival of neuronal cells. We investigated expression of NGF and its receptors, TrkA and p75NTR, in hepatocellular carcinomas (HCCs). Although hepatocytes and hepatic stellate cells (HSCs) showed respectively weak and intense NGF immunostaining in the background livers of patients suffering from liver cirrhosis (LC) or chronic hepatitis (CH), intense staining was demonstrated in HCC cells of 33 of 54 (61.1%) tumors. RT-PCR detected NGF mRNA in 7 freshly-isolated HCC samples, and in 2 of 4 cases, in which both background livers and tumors could be analyzed, NGF mRNA was more abundant in the tumors than the background livers. TrkA was detected in the smooth muscle cells of hepatic arteries, but it was negative in tumor cells as well as non-neoplastic hepatocytes. p75NTR and alpha-smooth muscle actin (alphaSMA) was expressed in HSCs in the background liver and fibroblast-like cells in stromal septa, whereas HSCs within the HCC tissues were mostly negative for p75NTR but positive for alphaSMA. This suggests that HSCs in HCC have a different property from those in background livers. Furthermore, the stromal septa contained abundant nerve fibers, which may be related to the increased NGF expression in HCC cells. NGF and its receptors are then thought to have a role in cellular interactions involving HCC cells, HSCs, arterial cells and nerve cells in HCC tissues.

Actins↗

Signaling function of PSGL-1 in neutrophil: tyrosine-phosphorylation-dependent and c-Abl-involved alteration in the F-actin-based cytoskeleton.

P-selectin glycoprotein ligand-1 (PSGL-1) is the best-characterized selectin ligand that has been demonstrated to mediate leukocytes rolling on endothelium and leukocytes recruitment into inflamed tissue in vivo. In addition to its direct role in leukocyte capturing, PSGL-1 also functions as a signal-transducing receptor. The present work showed that after cross-linking of PSGL-1 with KPL1, an anti-PSGL-1 monoclonal antibody, PSGL-1 linked to the cytoskeleton and became a detergent-insoluble component in activated neutrophils. The antibody cross-linking led to the polymerization and redistribution of F-actin-based cytoskeleton, and this alteration of cytoskeleton was spatiotemporally related to the polarization of PSGL-1. PSGL-1's polarization was cytoskeleton-dependent because it was eliminated by cytochalasin B. Furthermore, the polymerization and redistribution of F-actin filaments were tyrosine-phosphorylation-dependent since the alteration of F-actin-based cytoskeleton was severely blocked by genistein, a universal tyrosine kinase inhibitor. STI571, a small molecule inhibitor for cytoplasmic tyrosine kinase c-Abl, also inhibited the alteration of F-actin-based cytoskeleton, and c-Abl was redistributed to where F-actin concentrated in the activated neutrophils. The results suggested that cross-linking of PSGL-1 induces the phosphorylation-dependent and c-Abl-involved alteration of F-actin-based cytoskeleton in neutrophils.

Actins↗