Beier F, Eerola I, Vuorio E, Luvalle P, Reichenberger E, Bertling W, von der Mark K, Lammi M J
Institute for Experimental Medicine, University of Erlangen-Nürnberg, Germany.
Matrix Biol. 1996 Dec;15(6):415-22. doi: 10.1016/s0945-053x(96)90160-2.
The type X collagen gene is specifically expressed in hypertrophic chondrocytes during endochondral ossification. Transcription of the type X collagen gene by these differentiated cells is turned on at the same time as transcription of several other cartilage specific genes is switched off and before mineralization of the matrix begins. Analysis of type X collagen promoters for regulatory regions in different cell culture systems and in transgenic mice has given contradictory results suggesting major differences among species. To approach this problem, we have determined the nucleotide sequences of the two introns and upstream promoter sequences of the human and mouse type X collagen genes and compared them with those of bovine and chick. Within the promoter regions, we found three boxes of homology which are nearly continuous in the human gene but have interruptions in the murine gene. One of these interruptions was identified as a complex 1.9 kb repetitive element with homology to LINE, B1, B2 and long terminal repeat sequences. Regulatory elements of the human type X collagen gene are located upstream of the region where the repetitive element is inserted in the mouse gene, making it likely that the repetitive element is inserted between the coding region and regulatory sequences of the murine gene without interfering with its expression pattern. We also compared the sequences of the introns of both genes and found strong conservation. Comparisons of the mammalian sequences with promoter and first intron sequences of the chicken type X collagen gene revealed that only the proximal 120 nucleotides of the promoter were conserved, whereas all other sequences displayed no obvious homology to the murine and human sequences.
X型胶原基因在软骨内成骨过程中特异性表达于肥大软骨细胞。这些分化细胞对X型胶原基因的转录在其他几种软骨特异性基因转录关闭的同时开启，且在基质矿化开始之前。在不同细胞培养系统和转基因小鼠中对X型胶原启动子的调控区域进行分析，得到了相互矛盾的结果，这表明不同物种之间存在重大差异。为了解决这个问题，我们测定了人和小鼠X型胶原基因的两个内含子及上游启动子序列的核苷酸序列，并将它们与牛和鸡的序列进行比较。在启动子区域内，我们发现了三个同源框，在人类基因中它们几乎是连续的，但在小鼠基因中存在中断。其中一个中断被鉴定为一个复杂的1.9 kb重复元件，与LINE、B1、B2和长末端重复序列具有同源性。人类X型胶原基因的调控元件位于小鼠基因中重复元件插入区域的上游，这使得重复元件很可能插入到小鼠基因的编码区和调控序列之间，而不干扰其表达模式。我们还比较了两个基因内含子的序列，发现它们具有很强的保守性。将哺乳动物的序列与鸡X型胶原基因的启动子和第一个内含子序列进行比较，发现只有启动子近端的120个核苷酸是保守的，而所有其他序列与小鼠和人类序列没有明显的同源性。
