Analysis for transcript expression of meltrin alpha in normal, regenerating, and denervated rat muscle

Meltrin alpha (a disintegrin and metalloprotease (ADAM) 12) is a recently d iscovered molecule of the metalloprotease-disintegrin family which has been shown to participate in myotube formation in vitro and in myogenesis in vi vo. In this study we investigated meltrin alpha in regenerating rat muscle, which is a condition where satellite cells (SC) contribute to myofiber gro wth by fusing with one another and with myotubes or muscle fibers. We studi ed meltrin alpha mRNA expression by RT-PCR and in situ-hybridization in nor mal adult muscle, in soleus muscle regenerating for 2, 5, or 10 days, and i n muscle which had been denervated 1 week, 4 weeks, or 6 months previously. SC do not fuse after denervation. They detach from the principal muscle fi ber. Immunohistochemistry using an antibody against M-cadherin was performe d in parallel in order to identify SC. Messenger RNA as revealed by RT-PCR was absent in normal adult muscle, but present in regenerating and also in denervated muscle. Meltrin alpha transcript detected by in situ-hybridizati on was present in regenerating muscle only, not in normal or denervated mus cle. It was localized to SC. Taken together, meltrin alpha is absent in nor mal muscle, and localized to SC in fusing conditions. After denervation, th e transcript is upregulated. However, it is so lowly abundant that it fails to be detected by in situ-hybridization. This expression profile suggests a role for meltrin alpha in the fusion of SC with myotubes or muscle fibers , but not in SC adhesion to the adjacent myofiber in normal adult muscle.