Differential expression of FGF receptors and of myogenic regulatory factors in primary cultures of satellite cells originating from fast (EDL) and slow (Soleus) twitch rat muscles

In the rat, the fast and slow twitch muscles respectively Extensor digitoru m longus (EDL) and Soleus present differential characteristics during regen eration. This suggests that their satellite cells responsible for muscle gr owth and repair represent distinct cellular populations. We have previously shown that satellite cells dissociated from Soleus and grown in vitro prol iferate more readily than those isolated from EDL muscle. Fibroblast growth factors (FGFs) are known as regulators of myoblast proliferation and sever al studies have revealed a relationship between the response of myoblasts t o FGF and the expression of myogenic regulatory factors (MRF) of the MyoD f amily by myoblasts. Therefore, we presently examined the possibility that t he satellite cells isolated from EDL and Soleus muscles differ in the expre ssion of FGF receptors (FGR-R) and of MRF expression. FGF-R1 and -R4 were s trongly expressed in proliferating cultures whereas FGF-R2 and R3 were not detected in these cultures. In differentiating cultures, only -R1 was prese nt in EDL satellite cells while FGF-R4 was also still expressed in Soleus c ells, interestingly, the unconventional receptor for FGF called cystein ric h FGF receptor (CFR), of yet unknown function, was mainly detected in EDL s atellite cell cultures. Soleus and EDL satellite cell cultures also differe d in the expression MRFs. These results are consistent with the notion that satellite cells from fast and slow twitch muscles belong to different type s of myogenic cells and suggest that satellite cells might play distinct ro les in the formation and diversification of fast and slow fibres.