Fig. 1.

Chemokines and their receptors are expressed during in vitro myogenesis. (A) During myotube formation, the majority of myoblasts (red) terminally differentiate into myocytes (green) which migrate, adhere and fuse with one another to form small nascent myotubes with few nuclei (blue). Subsequently, nascent myotubes fuse with myocytes to form large mature myotubes with many nuclei (blue). (B) Primary mouse muscle cells were immunostained for eMyHC at different times in DM and the percentage of nuclei within eMyHC⁺ cells (differentiation index) was determined. By 16 hours in DM, most nuclei were in eMyHC⁺ cells. (C) The fusion index, or percentage of nuclei in myotubes, increased with time, and by 48 hours the majority of nuclei were within myotubes. (D) A real-time RT-PCR array was used to analyze the time-course of expression in vitro for 84 genes pertaining to chemokines. Positive results were obtained for 80 genes. Three patterns of expression were observed with mRNA steady state levels peaking at 16, 24 or 36 hours in DM, times of extensive differentiation and fusion. The number of genes with peak expression levels at each time point is shown. (E) Time course of expression for three representative genes peaking at 16 (CCR3), 24 (CXCR4) or 36 hours (IL13) in DM. Data are means ± s.e.m., n=3.