Haramoto Yoshikazu, Oshima Tomomi, Takahashi Shuji, Ito Yuzuru
Research Center for Stem Cell Engineering, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan.
Int J Dev Biol. 2014;58(9):705-11. doi: 10.1387/ijdb.150032yi.
The insulin-like growth factor binding protein (Igfbp) family consists of six members designated Igfbp1-6. Igfbps are involved in many vital biological functions. They physically interact with IGFs (IGF1 and IGF2) and act as carriers, thereby protecting IGFs from proteolytic degradation. Thus, they function as modulators of IGF activity. Furthermore, Igfbps have been reported to have IGF-independent activities. They interact with other proteins, including cell surface proteins, extra-cellular matrix proteins, and potentially intracellular molecules. In Xenopus tropicalis (X. tropicalis), only four igfbp genes (igfbp1, igfbp2, igfbp4, and igfbp5) have been identified, and their expression is not well characterized. We report that X. tropicalis genome lacks the igfbp3 and igfbp6 genes based on synteny analyses. We also examined the spatio-temporal expression patterns of igfbp genes in early X. tropicalis development. Expression analyses indicated that they are differentially expressed during early development. Each igfbp gene showed a characteristic spatial expression pattern. Except for igfbp5, they demonstrated overlapping expression in the pronephros. The Xenopus pronephros is composed of four domains (i.e., the proximal tubule, intermediate tubule, distal tubule, and connecting tubule). Our results showed that at least two igfbp genes are co-expressed in all pronephric domains, suggesting that redundant functions of igfbp genes are required in early pronephric kidney development.
胰岛素样生长因子结合蛋白（Igfbp）家族由六个成员组成，分别命名为Igfbp1 - 6。Igfbp参与许多重要的生物学功能。它们与IGF（IGF1和IGF2）发生物理相互作用并充当载体，从而保护IGF不被蛋白水解降解。因此，它们作为IGF活性的调节剂发挥作用。此外，据报道Igfbp具有不依赖IGF的活性。它们与其他蛋白质相互作用，包括细胞表面蛋白、细胞外基质蛋白以及潜在的细胞内分子。在热带爪蟾（X. tropicalis）中，仅鉴定出四个igfbp基因（igfbp1、igfbp2、igfbp4和igfbp5），并且它们的表达情况尚未得到很好的表征。基于同线性分析，我们报道热带爪蟾基因组缺乏igfbp3和igfbp6基因。我们还研究了igfbp基因在热带爪蟾早期发育过程中的时空表达模式。表达分析表明它们在早期发育过程中差异表达。每个igfbp基因都呈现出独特的空间表达模式。除了igfbp5外，它们在前肾中表现出重叠表达。热带爪蟾的前肾由四个区域组成（即近端小管、中间小管、远端小管和连接小管）。我们的结果表明，至少有两个igfbp基因在前肾的所有区域中共同表达，这表明igfbp基因在前肾早期发育中需要具有冗余功能。
