Changes in the satellite cells of the anuran tadpole tail muscles during metamorphosis.

The incidence and the ultrastructure of the satellite cells associated with red and white muscle fibres of the anuran (Rana japonica) tadpole tail were examined in three stages (hindlimb-bud, prometamorphic, and climax) during metamorphosis. In these three stages the satellite cells are found more frequently in the red fibres than in the white fibres. As metamorphosis proceeds, the incidence of the satellite cells decreases in both red and white fibres. The satellite cells in the hindlimb-bud stage have abundant cytoplasm rich in organelles. Cisternae of rough endoplasmic reticulum are often dilated. The intercellular space between the satellite cell and the muscle fibre is narrow and relatively constant (15-25 nm). Some satellite cells appear to be in the process of fusion with the muscle fibre. Cytoplasmic volume and organellar content are gradually reduced during metamorphosis. In the prometamorphic and climax stages, the intercellular space is in general gradually extended. It often exceeds 0.5 microns, and usually contains the basal lamina and fibrous materials. Some satellite cells have cytoplasmic processes that project into the interstitial space through a gap in the basal lamina.