FIGURE 2. Expression of β1-integrin and CXCR4 by skeletal muscle satellite cells.

(A) Single myofibers isolated from gastrocnemius or soleus muscles of C57BL mice were stained with anti-β1-integrin (green, top row, and red, middle row) or anti-CXCR4 (green, top and bottom rows) antibody, together with anti-laminin (red, top row) or anti-Pax7 (green, middle row and red, bottom row) and analyzed by fluorescence microscopy. Nuclei were marked by DAPI (blue). Open arrowheads denote β1-integrin⁺ or CXCR4⁺ cells (top row). Enlarged, merged images are shown at right (middle and bottom rows). (B) The average frequency of Pax7 and CXCR4 or Pax7 and β1-integrin co-expression by myofiber-associated cells was determined from analysis of 60 individual myofibers. Bar graphs depict the frequency of CXCR4-expressing (green) or β1-integrin-expressing (purple) myofiber-associated cells that also express Pax7 (Mean ± SEM), or the frequency of Pax7⁺ cells that also express CXCR4 (blue) or β1-integrin (orange). The majority (80-90%) of Pax7⁺ cells are also CXCR4⁺ and β1-integrin⁺ (bottom plot). Likewise, >90% of β1-integrin⁺ cells are also Pax7⁺, although only ~30% of CXCR4⁺ cells co-express Pax7 (top plot). Based on flow cytometric analysis, CXCR4⁺ cells that lack Pax7 expression appear for the most part to be CD45⁺ infiltrating inflammatory cells (data not shown), which exhibit no myogenic activity.