Shin Grace J, Wilson Nicole H
Brain Growth and Regeneration Lab, School of Biomedical Sciences, The University of Queensland, Brisbane, 4072, QLD, Australia.
J Mol Histol. 2008 Feb;39(1):105-13. doi: 10.1007/s10735-007-9138-x. Epub 2007 Sep 7.
Repulsive guidance molecule (RGM) a is a glycosylphosphatidylinositol (GPI)-anchored plasma membrane protein that has been implicated in chemorepulsive axon guidance. Although RGMa binds the transmembrane receptor Neogenin, the developmental events controlled by the RGMa-Neogenin interactions in vivo remain largely unknown. We have cloned full-length RGMa from Xenopus borealis for the first time and identified two homologous genes referred to as RGMa1 and RGMa2. Here we show RGMa1 overexpression at 2-cell-stage resulted in cell death, which lead to an early embryonic lethal phenotype of the embryos. Time-lapse photomicroscopy revealed that embryos began to show initial morphological defects from approximately 5 h post-fertilization (hpf) which was then followed by extensive blastomere cell death at approximately 11 hpf. This phenotype was rescued by simultaneous knock down of RGMa using translation blocking anti-sense morpholinos. Knock down of the RGMa1 receptor Neogenin in RGMa1 overexpressing embryos was also able to rescue the phenotype. Together these results indicated that RGMa1 was signalling through Neogenin to induce cell death in the early embryo. While previous studies have suggested that Neogenin is a dependence receptor that induces cell death in the absence of RGM, we have instead shown that Neogenin-RGM interactions induce cell death in the early embryo. The roles of RGMa1 and Neogenin appear to be context specific so that their co-ordinated and regulated expressions are essential for normal development of the vertebrate embryo.
排斥性导向分子（RGM）a是一种糖基磷脂酰肌醇（GPI）锚定的质膜蛋白，与化学排斥性轴突导向有关。尽管RGMa与跨膜受体新生蛋白结合，但体内由RGMa - 新生蛋白相互作用控制的发育事件仍 largely未知。我们首次从北方爪蟾中克隆了全长RGMa，并鉴定出两个同源基因，分别称为RGMa1和RGMa2。在这里，我们表明在2细胞期过表达RGMa1会导致细胞死亡，进而导致胚胎出现早期胚胎致死表型。延时显微镜观察显示，胚胎在受精后约5小时（hpf）开始出现初始形态缺陷，随后在约11 hpf时出现广泛的卵裂球细胞死亡。使用翻译阻断反义吗啉代寡核苷酸同时敲低RGMa可挽救此表型。在过表达RGMa1的胚胎中敲低RGMa1受体新生蛋白也能够挽救该表型。这些结果共同表明，RGMa1通过新生蛋白发出信号以诱导早期胚胎中的细胞死亡。虽然先前的研究表明新生蛋白是一种在没有RGM时诱导细胞死亡的依赖受体，但我们反而表明新生蛋白 - RGM相互作用在早期胚胎中诱导细胞死亡。RGMa1和新生蛋白的作用似乎具有上下文特异性，因此它们的协调和调节表达对于脊椎动物胚胎的正常发育至关重要。
