Fülöp C, Cs-Szabó G, Glant T T
Department of Biochemistry, Rush-Presbyterian-St. Luke's Medical Center, Chicago, IL 60612, USA.
Biochem J. 1996 Nov 1;319 ( Pt 3)(Pt 3):935-40. doi: 10.1042/bj3190935.
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 species, the EGF1 sequence has been detected only in human aggrecan transcripts. In this study we have used the nested primer reverse transcription-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 its significant expression level in human transcripts, the EGF1 sequence 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 present in the dog aggrecan gene. The expression level of the EGF1 exon in the aggrecan transcripts correlates with the strength of the polypyrimidine tract upstream of the exon. The EGF1 sequence also shows much less conservation between the species than the EGF2 sequence. The species-specific expression and high sequence variation of the EGF1 exon imply that this sequence is likely to code for an aggrecan domain having no cartilage-specific function.
聚集蛋白聚糖转录本包含两个可变剪接外显子，它们编码两个表皮生长因子样结构域（EGF1和EGF2）。虽然EGF2序列在不同物种中以统一水平表达，但EGF1序列仅在人类聚集蛋白聚糖转录本中被检测到。在本研究中，我们使用巢式引物逆转录PCR（RT-PCR）方法比较了EGF1外显子在人类、牛和犬聚集蛋白聚糖转录本中的表达。我们的结果表明，该外显子以物种特异性方式表达。除了在人类转录本中有显著表达水平外，如巢式引物RT-PCR所示，在一小部分牛聚集蛋白聚糖转录本中也能检测到EGF1序列。相比之下，尽管犬聚集蛋白聚糖基因中存在EGF1序列，但在犬聚集蛋白聚糖转录本中检测不到相同的模块。聚集蛋白聚糖转录本中EGF1外显子的表达水平与该外显子上游多嘧啶序列的强度相关。EGF1序列在物种间的保守性也比EGF2序列低得多。EGF1外显子的物种特异性表达和高度序列变异表明，该序列可能编码一个不具有软骨特异性功能的聚集蛋白聚糖结构域。
