M-cadherin transcription in satellite cells from normal and denervated muscle

Satellite cells (SC) in adult muscle are quiescent in the G0 phase of the cell cycle. In the present study we determined whether SC after denervation upregulate M-cadherin, an adhesion molecule that is upregulated with differentiation and fusion. We also monitored primary cultures of SC from denervated muscle for expression of the transcription factors of the MyoD family to determine whether SC from denervated muscle can be activated in vitro. Hindlimb muscles of rats were denervated under anesthesia, and rats were killed after 2-28 days. The SC of the denervated limbs were pooled and either assessed for M-cadherin mRNA by using real-time RT-PCR or cultured in vitro. The cultures were processed for RT-PCR or immunofluorescence for expression of the transcription factors of the MyoD family. Hindlimb muscles of M-cadherin knockout mice were denervated under anesthesia, mice were killed after 2-28 days, and cells were stained for beta-galactosidase activity by X-gal histochemistry. In vitro, primary SC cultures from rat muscle denervated for 2-28 days expressed transcripts of myf5, MyoD, myogenin, and MRF4 as SC from normal innervated muscle. In vivo, M-cadherin transcription was not upregulated in SC from denervated rat muscle when compared with normal muscle. Moreover, beta-galactosidase activity was not detected in denervated mouse muscle. The finding that SC do not upregulate M-cadherin after denervation supports the notion that they remain in the G(0) phase of the cell cycle in vivo. However, the cells retain the capacity to pass through the proliferative and differentiative program when robustly stimulated to do so in vitro.