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Expression of mRNA for plasminogen activators and protease nexin‐1 in innervated and denervated mouse skeletal muscle

Plasminogen activators (urokinase‐type, u‐PA and tissue‐type, t‐PA) are serine proteases that have been suggested to play important roles in synaptic remodeling. The enzymatic activity of u‐PA in particular has previously been shown to increase dramatically after denervation of skeletal muscle. Using 32P‐labeled riboprobes and Northern blots the expression of mRNA for u‐PA, t‐PA and the inhibitor protease nexin‐1 (PN‐1) has been studied in innervated and 1–10‐days denervated hind‐limb muscle from mouse. Using RNA extracted from innervated and 6‐days‐denervated mouse hemidiaphragm muscles the expression of these mRNAs has also been investigated in synaptic and extrasynaptic muscle regions. For both u‐PA and t‐PA the observed autoradiographic signals were similar for RNA extracted from innervated and denervated leg muscles. The signals were also similar for RNA extracted from perisynaptic and extrasynaptic regions of hemidiaphragm muscle but u‐PA signals were lower in denervated than in innervated hemidiaphragm. No such difference was observed for t‐PA. PN‐1 mRNA levels were also found to decrease after denervation in the hemidiaphragm but no substantial decrease was observed in denervated hind‐limb muscles. No difference was observed between PN‐1 expression in perisynaptic and extrasynaptic regions. The effect of denervation on PA enzymatic activity in skeletal muscle is therefore likely to be mediated at some post‐transcriptional level. J. Neurosci. Res. 66:457–463, 2001. © 2001 Wiley‐Liss, Inc.