The ultrastructure of collagen in the dermis of tight-skin (Tsk) mutant mice.

A recently discovered dominant mutation in C57/B10 mice called tight-skin (Tsk) results in hypertrophy of certain collagenous tissues including the dermis and hypodermis. The skin of heterozygotes (Tsk/+) is indurated and substantially stiffer than that of the normal animals (+/+). In this study, an electron microscopical comparison of the skin of these animals revealed that the fibrous architecture of the hypertrophic reticular dermis of Tsk/+ mice is more disorganized than that of the +/+ mice and in many areas, the collagen fibrils are more densely packed. The abundance of fibroblasts with distended endoplasmic reticulum in both the dermis and hypodermis of Tsk/+ mice is consistent with increased collagen synthesis. Several of the changes in the dermis and hypodermis of the Tsk/+ mice are similar to changes reported in sclerodermatous skin of man. Surprisingly, an apparent abnormality in the morphology of some of collagen fibrils in the skin of Tsk/+ mice was found to be at least as prevalent in the "normal" +/+ mice. The reticular dermis of both animals contain scattered fibrils which are much larger in diameter than normal and often have a twisted appearance resulting from either helical grooves in the surface of the fibril or discrete branches which twist about one another.