EVOLUTION OF MYOSIN FILAMENT ARRANGEMENTS IN VERTEBRATE SKELETAL-MUSCLE

A survey of skeletal muscles throughout craniates shows basic kinds of myosin filament arrangement, simple-lattice and superlattice, within the A-band of each sarcomere. Distribution of simple- and superlattice arrangements across a phylogeny of craniates suggests that the superl attice arrangement is primitive and that Amia and teleosts are derived in showing simple-lattice arrangements. Two taxa examined (Scyliorhin us and Acipenser) show both lattice types within the same organism imp lying that there is not a simple evolutionary transformation of one to the other fiber arrangement. We discuss the possible functional signi ficance of the different lattice types. We believe that the crossbridg es may have greater competition for actin binding sites in simple-latt ice muscles compared to the superlattice types. (C) 1996 Wiley-Liss, I nc.