Muscular dysgenesis in fowl: ultrastructural study of skeletal muscles in the crooked neck dwarf (cn/cn) mutant.

In vivo evolutive aspects of muscular dysgenesis were studied in normal and crooked neck dwarf (cn/cn) 7.5- to 20-day chick embryos. Wing, leg and breast muscles were processed for electron microscopy. It appears that the effects of the gene cn are expressed in the multinucleated cells as fine structural aberrations. Dilatation of the sarcotubular system, partial loss of the contractile elements and malorganization of the myofibrils are the major anomalies observed from day 7.5 to 18 of incubation. These changes do not constitute an abrupt phenomenon. Normal and diseased multinucleated cells always coexist in the same muscle specimen; however the frequency of the pathological cells augments with time. At the end of the incubation period, the poorly organized muscle tissue contains only morbid muscle cells. Phagocytosis or autolysis are absent.