Smooth muscle myosin heavy chain isoforms and their role in muscle physiology

Unlike vertebrate skeletal muscle, smooth muscle myosin heavy chain isoform s are encoded by a single gene. Alternative splicing of the primary transcr ipt from a single gene generates four smooth muscle myosin heavy chain isof orms. These isoforms differ both at the carboxyl terminus (SM1 and SM2 isof orms) and at the amino terminus (SM-A and SM-B isoforms). The smooth muscle myosin heavy chain isoforms are differentially expressed during smooth mus cle development and in different smooth muscle cell types. The mechanical p roperties of smooth muscle may be correlated with the myosin heavy chain co ntent/isoform expression. However, the precise function of each smooth musc le myosin heavy chain isoform to muscle contraction remains to be determine d. This review mainly focuses on the molecular basis of smooth muscle myosi n heavy chain isoform diversity, its expression during development and dise ase, and its role in muscle physiology. (C) 2000 Wiley-Liss, Inc.