SPECIES-SPECIFIC ALTERNATIVE SPLICING OF THE EPIDERMAL GROWTH FACTOR-LIKE DOMAIN-1 OF CARTILAGE AGGRECAN

Aggrecan transcripts contain two alternatively spliced exons that code for two epidermal growth factor-like domains (EGF1 and EGF2). Whereas the EGF2 sequence is expressed at a uniform level among different spe cies, the EGF1 sequence has been detected only in human aggrecan trans cripts. In this study we have used the nested primer reverse transcrip tion-PCR (RT-PCR) method to compare the expression of the EGF1 exon in human, bovine and dog aggrecan transcripts. Our results indicate that this exon is expressed in a species-specific manner. In addition to i ts significant expression level in human transcripts, the EGF1 sequenc e can be detected in a small portion of bovine aggrecan transcripts as shown with nested primer RT-PCR, In contrast, the same module is not detectable in dog aggrecan transcripts, although an EGF1 sequence is p resent in the dog aggrecan gene. The expression level of the EGF1 exon in the aggrecan transcripts correlates with the strength of the polyp yrimidine tract upstream of the exon. The EGF1 sequence also shows muc h less conservation between the species than the EGF2 sequence. The sp ecies-specific expression and high sequence variation of the EGF1 exon imply that this sequence is likely to code for an aggrecan domain hav ing no cartilage-specific function.