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 I I gene through alternative splicing of exon 2 in several different tis sues of 15-19-week-old fetuses. The highest expression levels of proco llagen alpha2(XI) and alpha1(II) mRNAs were detected in cartilage, but , using long exposure times, Northern hybridization revealed the prese nce of the approximately 5.3 kb procollagen alpha1(II) mRNA in most ti ssues analysed: calvarial and diaphyseal bone, striated and cardiac mu scle, skin, brain, lung, kidney, liver, small intestine and colon. Bot h alternatively spliced forms of the mRNA were present in these tissue s. In cartilage, the short form of the procollagen alpha1(II) mRNA (wi thout exon 2 sequences) was clearly more abundant, whereas in most of the non-cartilaginous tissues the long form was the predominant one. L ow levels of procollagen alpha2(XI) mRNA were also seen in non-cartila ginous tissues: calvarial and diaphyseal bone, kidney, skin, muscle, i ntestine, liver, brain, and lung. In all the other positive tissues ex cept brain cortex, both collagen II and XI transcripts were observed. The localization of collagen II and XI signals was identical in cartil age, kidney and skin. However, in cartilage the signal with collagen I I 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 alpha 2(XI) mRNAs in many tissues of developing human fetuses. Since the col lagen 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 collage n II gene in non-cartilaginous tissues relates to collagen XI producti on.