LOCALIZATION OF COLLAGEN TYPE-1, TYPE-2, AND TYPE-3 MESSENGER-RNAS INHUMAN HETEROTOPIC OSSIFICATION BY NONRADIOACTIVE IN-SITU HYBRIDIZATION

Heterotopic ossification is a metabolically active process which share s several properties of orthotopic bone formation and, therefore, repr esents an excellent model for the investigation of matrix components. A novel tool for studying the ossifying process at the level of transc ription is the technique of non-radioactive in situ hybridization. Usi ng digoxigenin labeled cDNA probes we investigated the distribution pa tterns of types I, II and III collagen mRNAs in heterotopic ossificati on of pressure sores of paraplegic patients. The three collagen mRNAs exhibited substantially divergent distribution patterns. Type I (al) c ollagen mRNA was predominantly detectable in preosteoblasts, prechondr oblasts and chondrocytes of the ossification zone. Type II (alpha1) co llagen mRNA was nearly exclusively found in cells of the chondrogenic lineage. Type III (alpha1) collagen mRNA was detectable at low levels in soft tissue, but was strongly expressed by prechondroblasts and cho ndrocytes of heterotopic cartilage. Our in situ hybridization experime nts provide evidence that chondrogenic cells in heterotopic ossificati on show a phenotypic alteration in collagen type expression. These res ults indicate that chondrocytes of heterotopic cartilage show a co-exp ression of types I (alpha1), II (alpha1) and III (alpha1) collagen mRN As.