Zhidkova N I, Justice S K, Mayne R
Department of Cell Biology, University of Alabama at Birmingham 35294, USA.
J Biol Chem. 1995 Apr 21;270(16):9486-93. doi: 10.1074/jbc.270.16.9486.
An analysis was performed of differential splicing of primary transcripts in the noncollagenous variable region located in the amino terminus of the pro-alpha 1(XI) and pro-alpha 2(XI) collagen chains. The results for the pro-alpha 2(XI) chain showed that human cartilage or fibroblasts in culture contain transcripts in which a single highly acidic exon encoding for 21 amino acids is present or absent. For the chicken pro-alpha 1(XI) chain a more complex pattern of alternative splicing was detected with six possible variants. Of special interest was the alternative use of two exons (called IIA and IIB) in which IIA encodes for 39 amino acids and is highly acidic (estimated pI = 3.2), whereas IIB encodes for 49 amino acids and is highly basic (estimated pI = 10.6). A similar alternative use of exon IIA or exon IIB was also observed for human chondrocytes. Northern blotting with probes specific for IIA or IIB showed that both exons are present in transcripts from cartilage but exon IIB is preferentially utilized in transcripts from tendon. Present results suggest that both the pro-alpha 1(XI) and pro-alpha 2(XI) chains of type XI collagen undergo limited processing in vivo and that the noncollagenous variable region is initially retained on the surface of the fibrils. Differential splicing in the variable region may potentially influence the interaction of collagen fibrils with other molecules of the extracellular matrix and more specifically with sulfated glycosaminoglycan chains or with hyaluronan. Such interactions may play a key role in establishing both the organization of the collagen fibrils within the extracellular matrix and in limiting the diameter of collagen fibrils.
对位于前α1(XI)和前α2(XI)胶原链氨基末端的非胶原可变区初级转录本的差异剪接进行了分析。前α2(XI)链的结果表明，培养的人软骨或成纤维细胞含有转录本，其中存在或不存在一个编码21个氨基酸的单一高酸性外显子。对于鸡的前α1(XI)链，检测到一种更复杂的可变剪接模式，有六种可能的变体。特别有趣的是两个外显子（称为IIA和IIB）的可变使用，其中IIA编码39个氨基酸且高度酸性（估计pI = 3.2），而IIB编码49个氨基酸且高度碱性（估计pI = 10.6）。在人软骨细胞中也观察到外显子IIA或外显子IIB的类似可变使用。用对IIA或IIB特异的探针进行Northern印迹分析表明，两个外显子都存在于软骨转录本中，但外显子IIB在肌腱转录本中优先被利用。目前的结果表明，XI型胶原的前α1(XI)和前α2(XI)链在体内都经历有限的加工，并且非胶原可变区最初保留在原纤维表面。可变区的差异剪接可能潜在地影响胶原原纤维与细胞外基质其他分子的相互作用，更具体地说是与硫酸化糖胺聚糖链或透明质酸的相互作用。这种相互作用可能在建立细胞外基质中胶原原纤维的组织以及限制胶原原纤维直径方面起关键作用。
