Myosin is a highly conserved, ubiquitous
protein found in all eukaryotic cells, where it provides the motor function for diverse movements such as cytokinesis, phagocytosis, and muscle contraction. All
myosins contain an amino-terminal motor/head domain and a carboxy-terminal tail domain. Due to the extensive number of different molecules identified to date,
myosins have been divided into seven distinct classes based on the properties of the head domain. One such class, class II
myosins, consists of the conventional two-headed
myosins that form filaments and are composed of two
myosin heavy chain (MYH) subunits and four
myosin light chain subunits. The MYH subunit contains the
ATPase activity providing energy that is the driving force for contractile processes mentioned above, and numerous MYH
isoforms exist in vertebrates to carry out this function. The MYHs involved in striated muscle contraction in mammals are the focus of the current review. The genetics, molecular biology, and biochemical properties of mammalian MYHs are discussed below. MYH gene expression patterns in developing and adult striated muscles are described in detail, as are studies of regulation of MYH genes in the heart. The discovery that mutant MYH
isoforms have a causal role in the human disease
familial hypertrophic cardiomyopathy (FHC) has implemented structure/function investigations of MYHs. The regulation of MYH genes expressed in skeletal muscle and the potential functional implications that distinct MYH
isoforms may have on muscle physiology are addressed.