OBSERVATIONS ON THE FINE STRUCTURE OF PHARYNGEAL MUSCLE IN THE PLANARIAN DUGESIA TIGRINA

Abstract

Pharyngeal muscle of the planarian Dugesia tigrina was studied by electron microscopy after osmium tetroxide fixation. The muscle cell was observed to contain one myofibril or bundle of myofilaments parallel to its longitudinal axis. The myofilaments were of two types, different in size and distribution. No Z lines or myofilament organization into cross or helical striations were seen. Dense bodies were seen as projections from an invagination of the plasma membrane and as dense lines parallel to the myofilaments. The muscle cells are surrounded by a plasma membrane which is structurally associated with dense body projections, with vesicles and cisternae of sarcoplasmic reticulum, and with synaptic nerve endings. The cell has sarcoplasmic projections perpendicular to its long axis; these projections are seen to contain the nucleus or mitochondria and granules. Mitochondria and granules are also seen in a sarcoplasm rim around the fibril. The dense bodies may serve as attachment for thin myofilaments and function in transmission of stimuli from plasma membrane to the interior of the fibril.

Selective amputation of the pharynx identifies a FoxA-dependent regeneration program in planaria

“…The planarian pharynx serves as both the entrance and exit to the digestive system and is a complex organ consisting of multiple tissues including neurons, muscle, epithelial cells and secretory cells (Hyman, 1951; Ishii, 1962; MacRae, 1963; Kido, 1964). The pharynx is a large cylindrical structure that clearly lacks dividing stem cells (Hay and Coward, 1975; Newmark and Sánchez Alvarado, 2000; Orii et al, 2005).…”

Anatomy of the Planarian Dugesia japonica I. The Muscular System Revealed by Antisera against Myosin Heavy Chains

“…Several descriptions of the muscular system of planarians at the light and electron microscopic levels have been published (for example, MacRae, 1963;Morita, 1965;Sarnat, 1984). In addition to the conventional methods, phalloidin conjugated with a fluorescent probe has been used for visualizing muscle fibers, and revealed the meshwork structure of the body-wall muscles in various planarians (Reiger et al ., 1994;Tyler and Hyra, 1998).…”

PHRED-1 is a divergent neurexin-1 homolog that organizes muscle fibers and patterns organs during regeneration

“…Pharyngeal muscle consists of three distinct types of fibers: longitudinal fibers running from the proximal to distal end, circular fibers that circumvent the pharynx, and radial fibers that connect the inner and outer lumens of the cylinder (Macrae, 1963) (Figure 2A, 2D, and 2G). Staining whole, extracted pharynges with the muscle monoclonal antibody Tmus13 (Bueno et al, 1997) revealed a network of fine, orthogonal fibers covering the surface of the pharynx in control animals (Figure 2B).…”

“…Instead, it appears to limit the thickness of myofibrils. Electron microscopy has shown that myofilaments within the pharynx can vary in width (Macrae, 1963). Knockdown of phred-1 causes defects in muscle fiber morphology, specifically thickening and disrupting their patterning.…”