Structural variation of type XII collagen at its carboxyl-terminal NC1 domain generated by tissue-specific alternative splicing

This paper reports the identification of two structural variations in the N C1 domain of rat and mouse type XII: collagen. The long NC1 domain encoding 74 amino acids showed homology to chicken type XII and XIV collagens. The short NC1 domain was composed of 19 amino acids. Through genomic DNA analys es, two alternative exons were identified, each of which contained the vari able NC1 sequence. With the amino-terminal NC3 splicing alternatives, we pr opose here a new descriptive nomenclature: types XIIA-1 and XIIB-1 which in clude a long NC1 sequence encoded by exon 1 (from the 3'-end), and types XI IA-2 and XIIB-2 which include a short NCI sequence encoded by exon 2, Types XIIA-1 and XIIB-1, the predominant transcripts in 15-day old mouse embryos , showed decreased expression in 17-day old embryos when type XIIB-2 expres sion was sustained at constant levels. In adult mice, type XIIB-1 associate s with ligament and tendon, whereas type XIIB-2 is expressed in various oth er tissues. The long NC1 domain contains an extended acidic region (pI = 3. 4) followed by a terminal basic region (pI = 13.8). Because the short NC1 d omain lacks these features, structural variations in the type XII collagen NC1 domain suggests different functional roles in a tissue-specific fashion .