ABSTRACT 

Fibroblast growth factors (FGFs) are thought  to play a key role in tissue differentiation and maturation. Thus, the expression of the four members of the high-affinity tyrosine kinase FGF receptor family (FGFRs) and of the low-affinity heparan sulfate proteoglycan binding sites, syndecan-1 and perlecan, was studied in the human skeletal muscle during development.  

Northern Blot analysis demonstrated a developmentally regulated expression of the mRNAs for FGFR-1, FGFR-3, FGFR-4,  whereas only traces of FGFR-2 mRNA were found. Each receptor type had a different developmental pattern suggesting an independent regulation. Signal for FGFR-3 only was retained in the adult muscle. Among the low-affinity FGF binding sites, perlecan was absent, whereas RNA transcript for syndecan-1 peaked at week 13 of gestation, after which a significant decrease was observed. 

Immunohistochemistry for FGFRs revealed that their localization changed with muscle maturation. At early embryonic stages, FGFR-3 and FGFR-4 had a scattered distribution in the tissue and FGFR-1 was found on myotube and myofibers plasma membranes. At later stages, FGFR-1 positivity decreased and was found in a few areas of the muscle, FGFR-3 was concentrated into the nuclei of some, but not all muscle fibers and FGFR-4 kept an association with plasma membrane. In adult tissue, weak positivity for FGFR-3 and FGFR-4 was observed in the connective tissue only.  

When immunocytochemistry was performed on human fetal myoblasts in culture, confocal microscope analysis revealed a  non homoge-neous cell membrane distribution of FGFRs. 

Taken together, the data strongly suggest that  developmentally regulated expression and cell distribution of FGF receptors play a role during muscle maturation. 

 Developmental Dynamics, 1998, 211:362-373