Lian J, Stewart C, Puchacz E, Mackowiak S, Shalhoub V, Collart D, Zambetti G, Stein G
Department of Biological Chemistry, Harvard Medical School, Children's Hospital Medical Center, Boston, MA 02115.
Proc Natl Acad Sci U S A. 1989 Feb;86(4):1143-7. doi: 10.1073/pnas.86.4.1143.
The osteocalcin gene encodes a 6-kDa polypeptide, which represents one of the most abundant noncollagenous bone proteins, and the present studies establish that osteocalcin mRNA is detected only in bone tissue. An osteocalcin gene was isolated from a rat genomic DNA library, and sequence analysis indicated that the mRNA is represented in a 953-nucleotide segment of DNA consisting of four exons and three introns. A modular organization of the 5' flanking sequences of the gene is reflected by the presence of at least three classes of regulatory elements, which include the following: (i) RNA polymerase II canonical sequences; (ii) a series of consensus sequences for hormone receptor binding sites and cyclic nucleotide responsive elements consistent with physiologic expression of the osteocalcin gene; and (iii) a 24-nucleotide sequence in the proximal promoter region with a CAAT motif as a central element. We have designated this highly conserved sequence as an "osteocalcin box" since only 2 nucleotide substitutions are found in the rat and human osteocalcin genes. We have demonstrated two factors regulating osteocalcin gene expression. First, a 200-fold increase occurs in normal fetal calvaria osteoblasts producing a mineralizing matrix, compared to confluent osteoblasts in a nonmineralizing matrix. Second, contained within the 600 nucleotides immediately upstream from the transcription start site are sequences that support a 10-fold stimulated transcription of the gene by 1,25-dihydroxyvitamin D.
骨钙素基因编码一种6 kDa的多肽，它是最丰富的非胶原蛋白骨蛋白之一，目前的研究证实骨钙素mRNA仅在骨组织中被检测到。从大鼠基因组DNA文库中分离出一个骨钙素基因，序列分析表明该mRNA由一个953个核苷酸的DNA片段所代表，该片段由四个外显子和三个内含子组成。该基因5'侧翼序列的模块化组织通过至少三类调控元件的存在得以体现，这些调控元件包括：(i) RNA聚合酶II的典型序列；(ii) 一系列与骨钙素基因生理表达一致的激素受体结合位点和环核苷酸反应元件的共有序列；以及(iii) 近端启动子区域中一个以CAAT基序为中心元件的24个核苷酸序列。我们将这个高度保守的序列命名为“骨钙素盒”，因为在大鼠和人类骨钙素基因中仅发现2个核苷酸替换。我们已经证明了两个调节骨钙素基因表达的因素。首先，与处于非矿化基质中的汇合成骨细胞相比，在产生矿化基质的正常胎儿颅骨成骨细胞中，骨钙素基因表达增加了200倍。其次，在转录起始位点上游紧邻的600个核苷酸内包含的序列能够支持1,25 - 二羟基维生素D对该基因转录产生10倍的刺激作用。
