Dwarfism in the Alaskan Malamute: ultrastructural features of dwarf growth plate chondrocytes

This study was performed in order to reexamine the ultrastructural morphology of the chondrocytes in the growth plates of dwarf Alaskan Malamutes and to obtain semiquantitative cytochemical data about the proteoglycans. Growth plates from age-matched dwarf and homozygous nonaffected Alaskan Malamutes were processed for routine transmission electron microscopy and also stained with ruthenium red. Chondrocytes in dwarf plates were observed to occur in clumps or cell nests. Within some of these nests, chondrocytes in the upper half of the zone of chondrocyte proliferation had bizarre shapes ranging from V-shaped to whorled or rounded. These chondrocytes contained profiles of markedly dilated rough endoplasmic reticulum (RER). Material within the RER cisternae stained positively with ruthenium red and was partially digestible with testicular hyaluronidase. The material could, therefore, represent either chondroitin sulfate or hyaluronate. The RER in these dwarf chondrocytes was not oriented parallel to the long axis of the cells; instead, it consisted of irregularly dilated cisternae. Granule counts performed on the zone of chondrocyte proliferation revealed a significant decrease in the number of ruthenium red granules in the interterritorial matrix of dwarf chondrocytes when compared to those of the homozygous nonaffected chondrocytes.