XENOPUS EGG LIGAND-ACTIVATED TRANSCRIPTION FACTORS

在两栖动物中，卵径向对称，但受精 触发卵子皮质的旋转，从而决定 两侧对称。在背侧，大的蛋黄小板会移动 向上，与动物杆状细胞质亲密接触。我们的 工作假说是背部卵黄可以释放少量的 激活核转录因子的疏水分子 受体家族。 维甲酸(RA)/甲状腺的八种核受体 荷尔蒙家族已从一个从日本血吸虫 非洲爪哇未受精的卵。使用功能分析，我们已经证明 其中两个是经典类型的维甲酸受体(RAR)和 另外两个是新型维甲酸X受体家族(RXRs)的成员。 对后一种蛋白质的抗体表明它会成为 定位于囊胚核的一小部分，导致 中胚层，特别是在背侧。母体的发现 维甲酸受体在体内分布不对称 发展，可能会导致更好地理解强大的致畸作用 类风湿因子在脊椎动物早期发育中的作用。 其他受体对应于所谓的孤儿受体， 其配基尚不清楚。它们的DNA结合顺序 区域强烈表明它们可能绑定到重叠的子集 由维甲酸受体激活的基因网络。身份的鉴定 母体孤儿受体的配体可能导致 新的形态致病原和致畸致畸因素的鉴定 脊椎动物中的畸形。 这项建议的目的是确定 母体视黄醇和孤儿受体的发育功能， 包括鉴定涉及的内源性配体分子， 研究它们的致畸作用、作用方式、 受体及其配体在发育卵子中的定位，以及 它们分离的分子机制。一些分子 将在此分析中使用技术，利用 两栖动物胚胎到实验操作的早期阶段 以及在后期阶段转基因小鼠的发展。

In amphibia the egg is radially symmetric, but fertilization triggers a rotation of the egg cortex that determines the aids of bilateral symmetry. On the dorsal side the large yolk platelets move upwards, coming in intimate contact with animal pole cytoplasm. Our working hypothesis is that the dorsal yolk could release small hydrophobic molecules that activate transcription factors of the nuclear receptor family. Eight nuclear receptors of the retinoic acid (RA)/thyroid hormone family have been isolated from a cDNA library prepared from unfertilized Xenopus eggs. Using functional assays we have shown that two of them are retinoic acid receptors (RARs) of the classical type and two others are members of the novel retinoid "X"receptor family (RXRs). An antibody against one of the latter proteins shows that it becomes localized to a small subset of blastula nuclei that gives rise to mesoderm, particularly on the dorsal side. The discovery of maternal retinoid receptors, which become asymmetrically distributed during development, may lead to a better understanding of the potent teratogenic effects of RA in early vertebrate development. The other receptors correspond to so-called orphan receptors, for which the ligand is not yet known. The sequence of their DNA binding regions strongly suggests that they may bind to an overlapping subset of the gene network activated by retinoid receptors. The identification of ligands for the maternal orphan receptors could result in the identification of new morphogens and teratogens that cause congenital malformation in vertebrates. The objective of this proposal is to ascertain the developmental function of maternal retinoid and orphan receptors, including the identification of the endogenous ligand molecules involved, the study of their teratogenic effects, their mode of action, the localization of receptors and their ligands in the developing egg, and the molecular mechanisms of their segregation. A number of molecular techniques will be used in this analysis, exploiting the accessibility of amphibian embryos to experimental manipulation at the early stages of development, and of transgenic mice at later stages.