Transient upregulation of connexin43 gap junctions and synchronized cell cycle control precede myoblast fusion in regenerating skeletal muscle in vivo
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The spatio-temporal expression of gap junction connexins (Cx) was investigated and correlated with the progression of cell cycle control in regenerating soleus muscle of Wistar rats. Notexin caused a selective myonecrosis followed by the complete recapitulation of muscle differentiation in vivo, including the activation, commitment, proliferation, differentiation and fusion of myogenic cells. In regenerating skeletal muscle, only Cx43 protein, out of Cx-s 26, −32, −37, −40, −43 and −45, was detected in desmin positive cells. Early expression of Cx43 in the proliferating single myogenic progenitors was followed by a progressive upregulation in interacting myoblasts until syncytial fusion, and then by a rapid decline in multinucleate myotubes. The significant upregulation of Cx43 gap junctions in aligned myoblasts preceding fusion was accompanied by the widespread nuclear expression of cyclin-dependent kinase inhibitors p21waf1/Cip1 and p27kip1 and the complete loss of Ki67 protein. The synchronized exit of myoblasts from the cell cycle following extensive gap junction formation suggests a role for Cx43 channels in the regulation of cell cycle control. The potential of Cx43 channels to stimulate p21waf1/Cip1 and p27kip1 is known. In the muscle, proving the involvement of Cx43 in either a direct or a bystander cell cycle regulation requires functional investigations.
KeywordsNotexin-induced regeneration Skeletal muscle differentiation Connexin43 gap junctions Cell cycle control Synchronized fusion
We are indebted to Professor Howard Evans (University of Wales) and Dr. Robert Gourdie (Charleston, S.C., USA) for providing us with their Cx specific antibodies, and to Mr. Daniel Ciantar (UCL), Mrs. Elizabet Balazshazi, Aniko Sarro, Maria Labdy and Katalin Danyi (University of Szeged) for skilful technical assistance. This work was supported by grants from The Royal Society of UK (15109) and OTKA of Hungary T32928.
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