Abstract
Myoblast fusion is fundamental to the development and regeneration of skeletal muscle. To fuse, myoblasts undergo cell-cell recognition and adhesion and merger of membranes between apposing cells. Cell migration must occur in advance of these events to bring myoblasts into proximity, but the factors that regulate myoblast motility are not fully understood. CD164 is a cell surface sialomucin that is targeted to endosomes and lysosomes via its intracellular region. In hematopoietic progenitor cells, CD164 forms complexes with the motility-stimulating chemokine receptor, CXCR4, in response to the CXCR4 ligand, CXCL12/SDF-1 (Forde, S., Tye, B. J., Newey, S. E., Roubelakis, M., Smythe, J., McGuckin, C. P., Pettengell, R., and Watt, S. M. (2007) Blood 109, 1825-1833). We have previously shown that CD164 stimulates myotube formation in vitro. We report here that CD164 is associated with CXCR4 in C2C12 myoblasts. Cells in which CD164 levels are increased or decreased via overexpression or RNA interference-mediated knockdown, respectively, show enhanced or reduced myotube formation and cell migration, the latter both basally and in response to CXCL12/SDF-1. Furthermore, expression of CD164 cytoplasmic tail mutants that alter the endosome/lysosome targeting sequence and, consequently, the subcellular localization in myoblasts, reveals a similar correlation between cell motility and myotube formation. Finally, Cd164 mRNA is expressed in the dorsal somite (the early myogenic compartment of the mouse embryo) and in premuscle masses. Taken together, these results suggest that CD164 is a regulator of myoblast motility and that this property contributes to its ability to promote myoblast fusion into myotubes.
Highlights
During vertebrate embryogenesis, skeletal muscle precursor cells originate in somites and undergo a multistep process of lineage commitment, migration, and differentiation into myo
Cd164 Is Expressed in Somites during Mouse Development— CD164 is expressed in myoblast cell lines [13], but little is known of its expression pattern during myogenesis in vivo
To determine whether Cd164 is expressed during early stages of skeletal muscle development, whole mount in situ hybridization was performed on mouse embryos at E9.5 and E10.5
Summary
Skeletal muscle precursor cells originate in somites and undergo a multistep process of lineage commitment, migration, and differentiation into myo-. Expression of CD164 cytoplasmic tail mutants that alter the endosome/lysosome targeting sequence and, the subcellular localization in myoblasts, reveals a similar correlation between cell motility and myotube formation.
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