THE importance of collagens in growth and differentiation1,2 and in cell adhesion3 is well documented. We have previously shown that cell-free, demineralised, collagenous bone matrix induces the formation of cartilage, bone and bone marrow4-6. One of the early responses to implanted collagenous matrix is the appearance of connective tissue mesenchymal cells adjacent to the implanted matrix before their differentiation into cartilage. We present here direct evidence that collagenous bone matrix is a local mitogen for connective tissue cells. We find that the collagenous bone matrix is a potent inducer of ornithine decarboxylase (EC 22.214.171.124, ODC), an enzyme involved in polyamine biosynthesis7 and considered as an early marker of cell proliferation8. These studies have been corroborated by incorporation of 3H-thymidine into acid-precipitable material and by autoradiography. Our results reveal the local influence of insoluble collagenous bone matrix on proliferation of mesenchymal cells and imply a role for this extracellular matrix in anchorage-dependent9 events in cell growth and differentiation.
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