PubMed · 7943965
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D W Burt. 1994. Mapping the chicken ACTA2 locus using heteroduplex polymorphisms.. https://doi.org/10.1111/j.1365-2052.1994.tb00120.x
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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.
1. Confocal microscopic studies of rat colonic mucosa showed that the pericryptal sheath surrounding distal colonic crypts is an effective barrier both to dextran and NaCl movement, whereas no such structure surrounds the caecal crypts. 2. The distal colonic pericryptal barrier was functionally demonstrated by accumulation of Sodium Green within the pericryptal space. After exposure to benzamil, Sodium Green accumulation was decreased. Fluorescein isocyanate-labelled dextran (FITC dextran; molecular mass 10000 Da) was accumulated in the crypt lumens and pericryptal spaces. Both dextran and Sodium Green accumulation were absent from the pericryptal zone surrounding caecal crypts. 3. Low dietary Na+ intake raised rat plasma aldosterone and stimulated distal pericryptal sheath growth and adhesiveness as shown by increased amounts of F-actin, smooth muscle actin, beta-catenin and E-cadherins in the pericryptal zone. It also raised the capacity of the distal colon to dehydrate against a high luminal hydraulic resistance. This linkage indicates that trophic effects on the colon resulting from a low Na+ diet are not confined solely to effects on transepithelial Na+ transport, but are observed in the pericryptal sheath. 4. A computer model of crypt function confirms that a pericryptal sheath with low permeability to NaCl is an essential component of the crypt dehydrating mechanism.
Monoclonal antibody (mAb) binding sites in the N-terminal actin-binding domain of utrophin have been identified using phage-displayed peptide libraries, and the mAbs have been used to probe functional regions of utrophin involved in actin binding. mAbs were characterized for their ability to interact with the utrophin actin-binding domain and to affect actin binding to utrophin in sedimentation assays. One of these antibodies was able to inhibit utrophin-F-actin binding and was shown to recognize a predicted helical region at residues 13-22 of utrophin, close to a previously predicted actin-binding site. Two other mAbs which did not affect actin binding recognized predicted loops in the second calponin homology domain of the utrophin actin-binding domain. Using the known three-dimensional structure of the homologous actin-binding domain of fimbrin, these results have enabled us to determine the likely orientation of the utrophin actin-binding domain with respect to the actin filament.