Anatomy of the planarian Dugesia japonica -: I.: The muscular system revealed by antisera against myosin heavy chains

The planarian Dugesia japonica has two genes encoding myosin heavy chain, DjMHC-A and B (Kobayashi et al., 1998). We produced antibodies specifically recognizing each myosin heavy chain protein using their carboxyl terminal regions expressed in E coli as antigens. Immunohistochemical analyses of sections and whole-mount specimens revealed the detailed structure and distribution of each type of muscle fiber in the planarian. In general, the MHC-A muscle fibers were distributed beneath the epithelial layers, namely, they were observable in the pharynx, the mouth, the intestine, the eyes and the body wall. In the pharynx, only MHC-A muscle fibers were present. In contrast, the MHC-B muscle fibers were distributed in the mesenchyme as dorso-ventral and transverse muscles, and in the body wall. The body-wall muscles were composed of an outer layer of circular MHC-A muscles and inner longitudinal and intermediate diagonal MHC-B muscle layers. Thus, two types of muscle fibers were distinguished by their distribution in the planarian.