16 Muscle: Structure, Function, and Development

Abstract

I. INTRODUCTION
Muscle cells are characterized by a filament-lattice structure that generates contractile force in a regulated manner. Caenorhabditis elegans contains several groups of muscles with diverse functions. The most numerous (95 in adults) are striated (multiple sarcomere) muscles used for locomotion of the animal. Eighty one of these body-wall muscles are present at birth, with the remainder added early during postembryonic development (Sulston and Horvitz 1977; Sulston et al. 1983). A variety of nonstriated (single-sarcomere) muscles are formed during embryogenesis. These muscles are used for diverse functions: pharyngeal pumping (20 pharyngeal muscle cells), intestinal contraction (2 intestinal muscles), and defecation control (1 anal sphincter and 1 anal depressor). During postembryonic development, the hermaphrodite adds a set of muscles for fertilization and egg laying (8 vulval and 8 uterine muscles and the contractile gonadal sheath), whereas the male adds a specialized set of 41 muscles to be used in mating. Anatomical simplicity has been a significant factor in the development of C. elegans as a model organism for studies of muscle. Due to the predominance of the body-wall muscle class, this class has been the most extensively analyzed; thus, much of the information in this chapter focuses on body-wall muscle.

Muscle has been a fertile ground for molecular genetic studies with C. elegans. Although muscle is essential for viability (see, e.g., Waterston 1989), partial muscle function is sufficient for growth under laboratory conditions. This allowed the isolation of many mutations affecting muscle (see, e.g., Brenner 1974; Epstein and Thomson 1974;...