Patterns of expression of the six alternatively spliced exons affecting the structures of the COL1 and NC2 domains of the alpha 1(XIII) collagen chain in human tissues and cell lines.
Reverse transcription-polymerase chain reactions and RNA protection experiments were used to examine alternative splicing of the six exons 3B-5, 12, and 13 affecting the COL1 and NC2 domains of type XIII collagen in seven human tissues and four cell lines. Distinct differences in the proportions of the variant mRNAs were found. With respect to the COL1 domain, all studied samples contained mRNAs corresponding to the shortest COL1 variants of 57 and 66 residues, with the former variant being prominent in most samples. Most of the samples also contained notable amounts of mRNAs that corresponded to the longest COL1 variants, mainly those of 104 and 95 residues. Particularly the extent of inclusion of exon 12 and 13 sequences, encoding most of the NC2 domain, varied according to the type of tissue or cell analyzed. Bone, cartilage, and colon adenocarcinoma samples contained little or none of the mRNAs corresponding to the long NC2 variants, whereas in fibroblast, lung, muscle, and osteosarcoma cells, those mRNAs were the major variants. The relative proportions of the various combinations of exons 3B-5, 12, and 13 were evaluated in four of the RNA samples. Interestingly, each of these samples appeared to contain only one to three major combinations of the six exons, representing about 40% to nearly 100% of all variants.