Yamashiro Sawako, Noguchi Tatsuhiko, Mabuchi Issei
Division of Biology, Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8902, Japan.
Cell Motil Cytoskeleton. 2003 May;55(1):36-50. doi: 10.1002/cm.10109.
Mammalian IQGAP1 is considered to modulate organization of the actin cytoskeleton under regulation of signaling proteins Cdc42 or Rac and calmodulin [Bashour et al., 1997: J Cell Biol 137:1555-1566; Hart et al., 1996: EMBO J 15:2997-3005] and also to be involved in cadherin-based cell adhesion [Kuroda et al., 1998: Science 281:832-835]. However, its function in the cell has not been clear. In order to clarify the function of IQGAP, we investigated IQGAP in Xenopus laevis cells. We isolated two Xenopus cDNAs encoding homologues of mammalian IQGAP, XIQGAP1, and XIQGAP2, which show high homology with human IQGAP1 and IQGAP2, respectively. Immunofluorescent localization of XIQGAPs in Xenopus tissue cultured cells (XTC cells) and in developing embryos was examined. In XTC cells, XIQGAP1 was colocalized with F-actin at cell-to-cell contact sites, membrane ruffles in lamellipodia, and filopodia. During development of embryos, XIQGAP1 was concentrated in the borders of all embryonic cells. An intense staining for XIQGAP1 was found in regions undergoing active morphogenetic movements, such as the blastopore lip of gastrulae, and the neural plate, the notochord, and the somite of neurulae. These results suggest that XIQGAP1 is involved in both cell-to-cell adhesion and cell migration during Xenopus embryogenesis and in cultured cells. On the other hand, the localization of XIQGAP2 in XTC cells was distinct from that of XIQGAP1 although it was also seen in lamellipodia, filopodia, and borders between cells. In addition to these regions, strong nuclear staining was observed in both XTC cells and embryonic cells.
哺乳动物的IQGAP1被认为在信号蛋白Cdc42或Rac以及钙调蛋白的调控下调节肌动蛋白细胞骨架的组织[Bashour等人，1997年：《细胞生物学杂志》137:1555 - 1566；Hart等人，1996年：《欧洲分子生物学组织杂志》15:2997 - 3005]，并且还参与基于钙黏蛋白的细胞黏附[Kuroda等人，1998年：《科学》281:832 - 835]。然而，它在细胞中的功能尚不清楚。为了阐明IQGAP的功能，我们在非洲爪蟾细胞中研究了IQGAP。我们分离出两个编码哺乳动物IQGAP同源物的非洲爪蟾cDNA，即XIQGAP1和XIQGAP2，它们分别与人IQGAP1和IQGAP2具有高度同源性。检测了XIQGAPs在非洲爪蟾组织培养细胞（XTC细胞）和发育胚胎中的免疫荧光定位。在XTC细胞中，XIQGAP1在细胞间接触部位、片状伪足中的膜皱褶和丝状伪足处与F - 肌动蛋白共定位。在胚胎发育过程中，XIQGAP1集中在所有胚胎细胞的边界。在经历活跃形态发生运动的区域，如原肠胚的胚孔唇、神经板、脊索和神经胚的体节中，发现XIQGAP1有强烈染色。这些结果表明，XIQGAP1在非洲爪蟾胚胎发育过程中和培养细胞中参与细胞间黏附和细胞迁移。另一方面，XIQGAP2在XTC细胞中的定位与XIQGAP1不同，尽管它也出现在片状伪足、丝状伪足和细胞间边界处。除了这些区域外，在XTC细胞和胚胎细胞中均观察到强核染色。
