Growth plate abnormalities in a new dwarf mouse model: tich

Growth plate cartilage calcification has been examined in a recently described mouse mutant, tich, which is co-isogenic with the A.TL strain. Long bones were studied from 1-day-old and 1-month-old mice which carried a homozygous recessive gene mutation making them short limbed and dumpy. Specimens were studied by routine histology, scanning electron microscopy and radiography. In 1-day-old tich mice the front of calcified cartilage was recessed behind the advancing periosteum and bone. No similar recess was seen in control mice. At 1 month of age, a number of the long bone growth plates were irregularly thickened, particularly in the central area. This produced a central tongue of non-calcified cartilage (particularly prominent in the proximal tibia) which gave rise to a corresponding pit in the calcified cartilage layer, in macerated specimens. This was accompanied by poor resorption of calcified cartilage. At both ages the presence of the respective defects was radiographically confirmed. At present it is not known whether this is primarily a defect of calcification or resorption but its presence, apparently from a single mutation in a genetically defined mouse strain, makes it a potentially valuable model.