Developmental regulation of mRNA species for types II, IX and XI collagens during mouse embryogenesis

Several techniques were used to study the co-ordination of mRNA levels for five constituent chains of cartilage collagen fibrils during mouse development. Short cDNA clones were first constructed for mouse and human alpha3(IX) and for mouse proalpha1(XI) collagen mRNA species. Northern analysis of developing mouse embryos revealed that the mRNA species for alpha1, alpha2 and alpha3 chains of type IX collagen peaked earlier than those for proalpha1(II) and proalpha1(XI) collagen chains. Quantification of these mRNA species by slot-blot hybridization confirmed this developmental regulation: the mRNA ratios for type II/type IX/type XI collagens changed from 5.7:1:0.6 (at embryonic day 12.5) to 10.6:1:0.9 (in newborn mice). However, the genes coding for the three chains of type IX collagen seemed to be under more co-ordinated regulation during mouse development. In addition to high mRNA levels in cartilages and the eye, low levels of type IX collagen transcripts were identified in brain and skin of newborn mouse using RNase protection and reverse transcriptase-PCR assays. Finally, hybridization in situ revealed identical tissue distributions of the three type IX collagen mRNA species during early chondrogenesis but somewhat more widespread expression of the alpha1(IX) and alpha3(IX) mRNA species during endochondral ossification at day 16.5 of embryonic development. These results suggest a relatively tight co-ordination of the alpha1(IX), alpha2(IX), and alpha3(IX) collagen mRNA species in chondrocytes, but a lack of co-ordination in several non-cartilaginous tissues.