title: In differentiating prefusion myoblasts connexin43 gap junction coupling is upregulated before myoblast alignment then reduced in post-mitotic cells.
abstract: Previously we have shown that during in vivo muscle regeneration differentiating rat primary myoblasts transiently upregulate connexin43 (Cx43) gap junctions and leave cell cycle synchronously. Here, we studied the temporal regulation of Cx expression in relation to functional dye coupling in allogenic primary myoblast cultures using western blotting, immuno-confocal microscopy and dye transfer assays. As in vivo, Cx43 was the only Cx isotype out of Cx26, 32, 37, 40, 43 and 45 found in cultured rat myoblasts by immunostaining. Cultured myoblasts showed similar temporal regulation of Cx43 expression and phenotypic maturation to those regenerating in vivo. Cx43 protein was progressively upregulated in prefusion myoblasts, first by the cytoplasmic assembly in sparse myoblast meshworks and then in cell membrane particles in aligned cells. Dye injection using either Lucifer Yellow alone, Cascade Blue with a non-junction permeant FITC-dextran revealed an extensive gap junction coupling between the sparse interacting myoblasts and a reduced communication between the aligned, but still prefused cells. The aligned myoblasts, uniformly upregulate p21(waf1/cip1) and p27(kip1) cell cycle control proteins. Taken together, in prefusion myoblasts less membrane-bound Cx43 was found to mediate substantially more efficient dye coupling in the growing cell fraction than those in the aligned post-mitotic myoblasts. These and our in vivo results in early muscle differentiation are consistent with the role of Cx43 gap junctions in synchronizing cell cycle control of myoblasts to make them competent for a coordinated syncytial fusion.
authors.affiliation: Department of Biochemistry, Faculty of Medicine, University of Szeged, Szeged, Hungary.
authors.forename: Aniko
authors.initials: A
authors.lastname: Gorbe
authors.forename: David L
authors.initials: DL
authors.lastname: Becker
authors.forename: Laszlo
authors.initials: L
authors.lastname: Dux
authors.forename: Laszlo
authors.initials: L
authors.lastname: Krenacs
authors.forename: Tibor
authors.initials: T
authors.lastname: Krenacs
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002454:Cell Differentiation; D002459:Cell Fusion; D002462:Cell Membrane / Q000737:chemistry; D002478:Cells, Cultured; D018031:Connexin 43 / Q000032:analysis* / Q000378:metabolism*; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism; D003593:Cytoplasm / Q000737:chemistry; D005456:Fluorescent Dyes / Q000032:analysis / Q000378:metabolism; D017629:Gap Junctions; D018613:Microscopy, Confocal; D008938:Mitosis; D032446:Myoblasts / Q000737:chemistry* / Q000166:cytology* / Q000378:metabolism; D051381:Rats; D015854:Up-Regulation
chemical_list: C493958:Cdkn1a protein, rat; D018031:Connexin 43; D050759:Cyclin-Dependent Kinase Inhibitor p21; D005456:Fluorescent Dyes; D050760:Cyclin-Dependent Kinase Inhibitor p27