The Journal of Bone and Joint Surgery, Vol 63, Issue 4 637-644, Copyright © 1981 by Journal of Bone and Joint Surgery, Inc
Ultrastructural studies of cartilage matrix in mice homozygous for chondrodysplasia
CB Monson and RE Seegmiller
The absence of columns of proliferative chondrocytes in mice with
hereditary chondrodysplasia (cho/cho) has been attributed to a lack of
structural integrity of the cartilage matrix. To determine whether the
abnormality is related to defective interaction between proteoglycan and
collagen, sternal cartilage from control and mutant fetuses at eighteen
days of gestation was examined with autoradiographic and ultrastructural
methods. The sulphate-labeling pattern in the mutant fetuses was normal,
suggesting that the defect is not due to regional differences in
proteoglycan synthesis. The presence of ruthenium red-stained matrix
granules precipitated one collagen fibrils suggests that proteoglycan is
capable of interacting with collagen in the mutant's matrix. The absence of
a pericellular space and the presence of collagen fibrils adjacent to the
external surface of the cell membrane suggests that the defect is due to
precocious assembly of collagen monomers into fibrils, resulting in the
absence of a normal network of interconnecting collagen fibrils and
proteoglycan. Further studies are necessary to test this hypothesis.
CLINICAL RELEVANCE: Because the phenotype of this mutation resembles
certain forms of human skeletal dysplasia, mice with hereditary
chondrodysplasia may serve as a model to elucidate the molecular mechanism
for certain recessive disorders of chondrogenesis. In this regard, a much
improved understanding of gene action is needed before effective treatment
and corrective procedures can be applied to the eighty or more clinical
forms of hereditary skeletal dysplasia.
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