Fine structure of mutant (muscular dysgenesis) embryonic mouse muscle

This investigation is concerned with the ultrastructure of embryonic muscle cells in mice homozygous for the mutation mdg (muscular dysgenesis). The earliest abnormalities are detected at a gestational age of 14 days when the sarcoplasmic reticulum of mutant cells begins to appear dilated. In later stages swollen sarcoplasmic reticulum is seen in all muscle cells as well as nuclear abnormalities and cell death. The correlation between the ultrastructural abnormalities of the sarcoplasmic reticulum and the other cellular abnormalities is discussed, as well as the possible relevance of the structural abnormalities to the total absence of muscle function in mutant homozygotes.