REGULATION OF PROTHROMBIN, THROMBIN RECEPTOR, AND PROTEASE NEXIN-1 EXPRESSION DURING DEVELOPMENT AND AFTER DENERVATION IN MUSCLE

Prothrombin, thrombin receptor (ThR), and protease nexin-1 (PN-1) mRNA levels in mouse muscle were quantified using competitive reverse tran scriptase-polymerase chain reaction during development and after dener vation to examine the possible role of thrombin in activity-dependent synapse elimination at the neuromuscular junction, The results showed that the levels of prothrombin and ThR were maximal at birth and decre ased by tno orders of magnitude by postnatal day 20 (P20), The level o f PN-1 mRNA was fairly constant during development except for a 4-fold to 5-fold downregulation at P10 and P15, the periods of maximal synap se elimination at the rodent neuromuscular junction, The expression of prothrombin mRNA in muscle at birth was 41-fold and 22-fold lower tha n those of ThR and PN-1, respectively, and the level of difference bet ween prothrombin and PN-1 reached almost three orders of magnitude at adulthood, Denervation of adult muscle resulted in a reversal of the r elative expression levels of the three genes, There were rapid 8-fold and 10-fold increases in prothrombin and ThR mRNA, respectively, and a 2-fold decrease in PN-1 mRNA. The changes in mRNA levels of the three genes after denervation indicated that these genes were regulated in a innervation-dependent manner and that nerve activity may play an imp ortant regulatory role in the expression of prothrombin, ThR, and PN-1 , The concurrent regulation of prothrombin and ThR suggests that throm bin-mediated cellular activities in muscle may be affected via the act ivation of ThR, An elevated le, el of local thrombin or thrombin-like activity might result from the decreased inhibitory activity of PN-1 d uring the period of peak synapse elimination in muscle development, J, Neurosci, Res, 53:304-311, 1998. (C) 1998 Wiley-Liss, Inc.(dagger.)