3-DIMENSIONAL CYTOARCHITECTURE OF COMPLEX BRANCHED FIBERS IN SOLEUS MUSCLE FROM MDX MUTANT MICE

Three-dimensional cytoarchitecture and types and features of muscle fi bers were examined in soleus muscles from mdx mutant mice at different stages of development. In the 2-week-old mice, no abnormal muscle fib ers were observed light microscopically, whereas in the 4-week-old ani mals, disrupted fibers were frequent in light microscopy and scanning electron microscopy. Muscle fibers fused with several short fiber bran ches appeared at the sixth week after birth and increased in number un til the tenth week. In the 1-year-old mice, approximately ten or more muscle fibers were seen fused together. They had many complex branches forming an ''anastomosing syncytial reticulum.'' Muscle fibers with i rregular diameters and aggregations of the same type fibers were also observed. Our results demonstrated that these complex branched fibers might be formed by long term repetition of the degeneration and regene ration cycle during the development of soleus muscles, indicating that the characteristic features of muscle fibers with irregular diameters and aggregations of the same type fibers are certainly dependent on t he existence of the complex branched fibers. (C) 1993 Wiley-Liss, Inc.