Expression of type VI, IX and XI collagen genes and alternative splicing of type II collagen transcripts in fracture callus tissue in mice

The levels of six mRNAs coding for constituent α-chains of three minor collagens of cartilage were analyzed in an experimental fracture model in normal and transgenic Del1 mice harboring a deletion mutation of exon 7 in the type II collagen gene. Reduced and retarded chondrogenesis in Del1 mice was evident in callus samples as reduced mRNA levels for the cartilage specific type IX and XI collagens at days 7 and 9 of fracture healing. Analysis of the calluses for alternative splicing of proα1(II) collagen mRNA also suggested retarded chondrogenesis in Del1 calluses. Another developmentally regulated step in limb development, a switch between alternative promoters of the α1(IX) collagen gene, was also seen during fracture healing but was less obvious in Del1 calluses. Finally, the current data suggest that the abnormality in bone remodelling in Del1 mice involves activation of the genes coding for α1(XI) and α2(VI) collagens.