COEXPRESSION OF COLLAGEN-II AND COLLAGEN-XI AND ALTERNATIVE SPLICING OF EXON-2 OF COLLAGEN-II IN SEVERAL DEVELOPING HUMAN TISSUES

Northern analyses, RNAase protection assays and in situ hybridizations were used to study the expression of the mRNA for the alpha2 chain of collagen XI and the two different mRNAs generated from the collagen II gene through alternative splicing of exon 2 in several different tissues of 15-19-week-old fetuses. The highest expression levels of procollagen alpha2(XI) and alpha1(II) mRNAs were detected in cartilage, but, using long exposure times, Northern hybridization revealed the presence of the approximately 5.3 kb procollagen alpha1(II) mRNA in most tissues analysed: calvarial and diaphyseal bone, striated and cardiac muscle, skin, brain, lung, kidney, liver, small intestine and colon. Both alternatively spliced forms of the mRNA were present in these tissues. In cartilage, the short form of the procollagen alpha1(II) mRNA (without exon 2 sequences) was clearly more abundant, whereas in most of the non-cartilaginous tissues the long form was the predominant one. Low levels of procollagen alpha2(XI) mRNA were also seen in non-cartilaginous tissues: calvarial and diaphyseal bone, kidney, skin, muscle, intestine, liver, brain, and lung. In all the other positive tissues except brain cortex, both collagen II and XI transcripts were observed. The localization of collagen II and XI signals was identical in cartilage, kidney and skin. However, in cartilage the signal with collagen II probe was much higher than that with the collagen alpha2(XI) probe. In epidermis the situation was reversed. Our results show considerable co-expression and co-localization of procollagen alpha1(II) and alpha2(XI) mRNAs in many tissues of developing human fetuses. Since the collagen alpha1(II) gene also codes for the alpha3(XI) chain of collagen XI we propose that some, but not all, of the expression of the collagen II gene in non-cartilaginous tissues relates to collagen XI production.