XENOPUS EGG LIGAND-ACTIVATED TRANSCRIPTION FACTORS

两栖类的卵是径向对称的， 触发了卵皮质的旋转， 左右对称 在背侧，大的卵黄板移动 向上，与动物极细胞质紧密接触。 我们 工作假设是，背卵黄可以释放小 激活核转录因子的疏水分子 受体家族 八种维甲酸核受体（RA）/甲状腺 已经从制备cDNA文库中分离了激素家族， 未受精的爪蟾卵 使用功能测定，我们已经表明， 其中两种是经典型视黄酸受体（RAR）， 另外两个是新的类视色素"X"受体家族（RXR）的成员。 针对后一种蛋白质的抗体显示， 位于囊胚细胞核的一个小的子集， 中胚层，特别是在背侧。 母性的发现 类维生素A受体，它成为不对称分布， 发展，可能会导致更好地了解潜在的致畸 RA对早期脊椎动物发育的影响。 其他受体对应于所谓的孤儿受体， 其配体尚不清楚。 它们的DNA结合序列 区域强烈表明，它们可能结合到一个重叠的子集， 由维甲酸受体激活的基因网络。 的识别 母体孤儿受体的配体可能导致 导致先天性畸形新形态因子和致畸因子的鉴定 脊椎动物畸形。 这项建议的目的是确定 母体类维生素A和孤儿受体的发育功能， 包括鉴定所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中的定位，以及 它们分离的分子机制。 值的数量的分子 技术将用于此分析，利用的可访问性 两栖动物胚胎在早期阶段的实验操作 发育，以及后期的转基因小鼠。

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.