MYOFIBRILLOGENESIS IN PRIMARY TISSUE-CULTURES OF ADULT HUMAN SKELETAL-MUSCLE - EXPRESSION OF DESMIN, TITIN, AND NEBULIN

To investigate the in vitro development of myofibrils in skeletal musc le cells derived from adult human muscle biopsies, immunohistochemical analysis was performed using monoclonal antibodies against desmin, ti tin, and nebulin. Diffuse desmin reactivity was detected 48 h after pl ating in about 60% of all mononucleated cells. This supports the use o f desmin as a marker for undifferentiated rhabdomyosarcomas in man. Ti tin was visible from day 4 onwards, while nebulin was not found in mon onucleated cells. After 1 week polynucleated myotubes appeared, and gr ew up to 30 days. Desmin was distributed diffusely throughout the cyto plasm until day 21, when the pattern became patchy. Titin began to be organized in a predominantly longitudinal orientation at day 15, while nebulin, which appeared for the first time in fusing myoblasts on the fifth to the seventh day, was almost immediately organized in a dotte d longitudinal pattern, which became a Z line connected striation in m atured myotubes.