Unique expression patterns of myosin heavy chain genes in the ductus arteriosus and uterus of rabbits

In smooth muscle tissue, two smooth muscle myosin heavy chain (MHC) isoform s (SMI, SM2) and two non-muscle MHC isoforms (NMA, NMB) have been identifie d. The purpose of our study was to clarify whether smooth muscle MHC mRNA e xpression reflects the physiological and functional state of the muscle. We studied the expression pattern of MHC mRNAs, using the S1-nuclease mapping procedure, in functionally and morphologically changeable organs; the duct us arteriosus (DA) during development (25 and 29 days of gestation, and fro m 3-day-old neonates) and uteri from virgin, day-10 pregnant (P10) and day- 29 pregnant (P29) rabbits. The results demonstrated that SM2 expression was greater in the fetal DA than in the fetal aortic and pulmonary arteries, b ut that it decreased significantly following closure of DA. In the gravid u terus, SMI expression was significantly (P<0.05) strong compared to other M HC mRNAs from virgin to P10 rabbits. During pregnancy, NMB expression showe d a tendency to increase until PIG, and after PIG, SM2 expression increased dramatically and NMB expression decreased to give almost a mirror image of the SM2 expression. Smooth muscle type (SM1, SM2) was significantly (P<0.0 5) strong compared to non-muscle type expression (NMA, NMB) at P29. These d ata suggest that smooth muscle MHC mRNA, especially SM2 expression reflects the physiological and functional state of the smooth muscle.