EXTENSIVE ALTERNATIVE SPLICING WITHIN THE AMINO-PROPEPTIDE CODING DOMAIN OF ALPHA-2(XI) PROCOLLAGEN MESSENGER-RNAS - EXPRESSION OF TRANSCRIPTS ENCODING TRUNCATED PRO-ALPHA CHAINS

Heterogeneity in type XI procollagen structure is extensive because al l three alpha(XI) collagen genes undergo complex alternative splicing within the amino-propeptide coding domain, Exon 7 of the human and exo ns 6-8 of the mouse alpha 2(XI) collagen genes, encoding part of the a mino-propeptide variable region, have recently been shown to be altern atively spliced. We show that exon 6-containing mRNAs for human alpha 2(XI) procollagen are expressed at 28 weeks in fetal tendon and cartil age but not at 38-44 days or 11 weeks, In the mouse, exon 6 is express ed in chondrocytes from 13.5 days onward, We recently identified conse rved sequences within intron 6 of the human and mouse alpha 2(XI) coll agen genes, containing additional consensus splice acceptor and donor sites that potentially increase the size of exon 7, dividing it into t hree parts, designated 7A, 7B, and 7C. We show by reverse transcriptio n polymerase chain reaction and in situ hybridization that these poten tial splice sites are used to yield additional alpha 2(XI) procollagen mRNA splice variants that are expressed in fetal tissues, In human, e xpression of exon 7B-containing transcripts may be developmental stage -specific, Interestingly, inclusion of exon 7A or exon 7B in human and mouse alpha 2(XI) procollagen mRNAs, respectively, would result in th e insertion of an in-frame termination codon, suggesting that some of the additional splice variants encode a truncated pro-alpha 2(XI) chai n.