02 April 2014
Vol 6, Issue 230

About The Cover

Cover image expansion

ONLINE COVER Muscle Building. A single, striated skeletal muscle fiber protrudes from a fascicle—a structure, found in skeletal muscle that consists of a collection of muscle fibers (myofibers) surrounded by connective tissue (shown in the background). Each myofiber is a skeletal muscle cell wrapped by a specialized plasma membrane called the sarcolemma, shown as pink tissue surrounding bundles of myofibrils (or myofilaments), shown as red ovals in the sarcoplasm along with other organelles [such as the nucleus (gray) and mitochondria (tan)]. Myofibrils consist of actin and myosin filaments (red dots), which contribute to the striated appearance of skeletal muscle tissue. The sarcolemma is the site of action potential conduction, which triggers muscle contraction. The dystrophin protein, which is defective in Duchenne muscular dystrophy (DMD), is located between the sarcolemma and myofilaments and links actin filaments to proteins on the inner surface of the sarcolemma. In this week's Focus, Hoffman and McNally discuss the state of dystrophin exon skipping as a therapy for DMD. Exon skipping occurs in the nucleus of the myofiber and is achieved with the use of oligonucleotides that restore production of the dystrophin protein, which is essential for skeletal muscle form and function. [CREDIT: V. ALTOUNIAN/SCIENCE TRANSLATIONAL MEDICINE]