Lin J J, Maeda R, Ong R C, Kim J, Lee L M, Kung H, Maéno M
Department of Basic Sciences, SAIC, National Cancer Institute-Frederick Cancer Research and Development Center, MD 21702-1201, USA.
Dev Growth Differ. 1997 Feb;39(1):43-51. doi: 10.1046/j.1440-169x.1997.00006.x.
Previously we have isolated a Xenopus cDNA homolog of bone morphogenetic protein-1 (XBMP-1A). In the present report we describe a new cDNA clone called XBMP-1B (or Xtld) from a Xenopus embryonic library. Sequence analysis indicates that these two clones share an indentical N-terminal sequence, including a region of metalloprotease domain, three copies of a repeat first found in complement proteins C1r/s and an epidermal growth factor (EGF)-like sequence. XBMP-1B protein has an additional copy of an EGF-like sequence followed by two copies of complement 1 r/s repeat in the C-terminus. The overall protein structure predicted from the XBMP-1B sequence reveals that it encodes a protein homologous to Drosophila tolloid. Three XBMP-1 transcripts (2.9, 5.2 and 6.6 kb) were detected by northern blot analysis. However, the 2.9 kb transcript hybridized specifically with XBMP-1A and the 5.2 and 6.6 kb transcripts hybridized with XBMP-1B. In Drosophila, a major function of tolloid is to augment the activity of the decapentaplegic gene product, a close relative of tumor growth factor (TGF)-beta superfamily members, BMP-2/4. Although XBMP-1 and XBMP-4 are detected in various adult tissues of Xenopus, the expression pattern of these two genes was not tightly correlated. In the embryo, the expression of XBMP-1 increased gradually from the morula to the swimming tadpole stages. Injection of XBMP-1B RNA into the ventral blastomeres at the 4-cell stage caused an elongation of the ventral marginal zone explants and converted globin-positive blood cells to mesenchymal and muscle tissues at later stages. It was shown that XBMP-1A was less active and a 1A mutant lacking the signal sequence was inactive. Further studies revealed that injection of XBMP-1B RNA into the ventral marginal zone induced up-regulation of dorsal marginal zone markers, such as goosecoid and chordin, at the gastrulation stage. These data indicate that XBMP-1 may have a role in determining dorso-ventral patterning in Xenopus, but in a different way from the dpp/tolloid system demonstrated in Drosophila.
此前我们已从非洲爪蟾中分离出骨形态发生蛋白-1（XBMP-1A）的cDNA同源物。在本报告中，我们描述了一个从非洲爪蟾胚胎文库中获得的名为XBMP-1B（或Xtld）的新cDNA克隆。序列分析表明，这两个克隆具有相同的N端序列，包括一个金属蛋白酶结构域区域、在补体蛋白C1r/s中首次发现的重复序列的三个拷贝以及一个表皮生长因子（EGF）样序列。XBMP-1B蛋白在C端还有一个额外的EGF样序列拷贝，随后是补体1r/s重复序列的两个拷贝。根据XBMP-1B序列预测的整体蛋白质结构表明，它编码一种与果蝇类tolloid蛋白同源的蛋白质。通过Northern印迹分析检测到三种XBMP-1转录本（2.9、5.2和6.6 kb）。然而，2.9 kb的转录本与XBMP-1A特异性杂交，5.2和6.6 kb的转录本与XBMP-1B杂交。在果蝇中，类tolloid蛋白的主要功能是增强脱翅基因产物的活性，脱翅基因产物是肿瘤生长因子（TGF）-β超家族成员BMP-2/4的近亲。虽然在非洲爪蟾的各种成年组织中都检测到了XBMP-1和XBMP-4，但这两个基因的表达模式并没有紧密相关。在胚胎中XBMP-1的表达从桑椹胚到游动蝌蚪阶段逐渐增加。在4细胞阶段将XBMP-1B RNA注射到腹侧卵裂球中，导致腹侧边缘区外植体伸长，并在后期将珠蛋白阳性血细胞转化为间充质和肌肉组织。结果表明，XBMP-1A活性较低，而缺失信号序列的1A突变体无活性。进一步研究表明，在原肠胚形成阶段将XBMP-1B RNA注射到腹侧边缘区可诱导背侧边缘区标记物如鹅膏蕈碱和脊索蛋白的上调。这些数据表明，XBMP-1可能在非洲爪蟾背腹模式的决定中起作用，但方式不同于果蝇中所示的dpp/类tolloid系统。
