Tata J R, James T C, Watson C S, Williams J L, Wolffe A P
Ciba Found Symp. 1983;98:96-110. doi: 10.1002/9780470720790.ch7.
Yolk proteins are the most abundant egg proteins in oviparous animals. They are deposited during oocyte maturation for use after fertilization and are synthesized in the liver or fat body as a common precursor termed vitellogenin. Hybridization with cloned DNA complementary to vitellogenin messenger RNA has revealed a surprisingly high degree of evolutionary conservation of sequence of vitellogenin genes among insects, amphibians and birds. The synthesis of vitellogenin in vertebrates is directly under the control of oestrogen at the level of gene transcription. In the frog, Xenopus, vitellogenin genes occur as a multigene family, four of which are actively expressed and are grouped as A and B genes. This multiplicity offers a useful system for investigating the possible selective hormonal regulation of expression of individual members of multigene families. When X. laevis vitellogenin genes were activated by oestrogen in the liver of whole animals or in cultures of parenchymal cells, the two groups of expressed genes were not induced in an identical manner in cells from male and female animals. The activation of A and B groups of genes was non-coordinate in male hepatocytes and coordinate in female cells. Prior exposure of male hepatocytes to oestradiol in vivo or in culture caused the pattern of expression to shift to that in female cells. Since the X. laevis oocyte itself does not synthesize vitellogenin in response to oestrogen, an attempt was made to activate its dormant vitellogenin genes by transferring oestrogen-binding proteins from the liver. Preliminary results show that the microinjection into the oocyte of a preparation containing liver receptor-hormone complex led to the synthesis of vitellogenin by the oocyte. Extension of these experiments will not only enable a more precise analysis of the activation of the vitellogenin multigene family to be made but will also provide direct functional evidence for the role played by steroid hormone receptors in regulating gene expression.
卵黄蛋白是卵生动物中最丰富的卵蛋白。它们在卵母细胞成熟过程中沉积，供受精后使用，并在肝脏或脂肪体中作为一种称为卵黄原蛋白的共同前体合成。与克隆的与卵黄原蛋白信使核糖核酸互补的DNA杂交显示，在昆虫、两栖动物和鸟类中，卵黄原蛋白基因的序列在进化上具有惊人的高度保守性。脊椎动物中卵黄原蛋白的合成在基因转录水平上直接受雌激素控制。在青蛙非洲爪蟾中，卵黄原蛋白基因以多基因家族的形式存在，其中四个基因被积极表达，并分为A基因和B基因。这种多样性为研究多基因家族单个成员表达的可能选择性激素调节提供了一个有用的系统。当非洲爪蟾卵黄原蛋白基因在完整动物的肝脏或实质细胞培养物中被雌激素激活时，两组表达基因在雄性和雌性动物的细胞中诱导方式并不相同。A组和B组基因在雄性肝细胞中的激活是非协同的，而在雌性细胞中是协同的。雄性肝细胞在体内或体外预先暴露于雌二醇会导致表达模式转变为雌性细胞中的模式。由于非洲爪蟾卵母细胞本身不会因雌激素而合成卵黄原蛋白，因此尝试通过转移来自肝脏的雌激素结合蛋白来激活其休眠的卵黄原蛋白基因。初步结果表明，将含有肝脏受体-激素复合物的制剂显微注射到卵母细胞中会导致卵母细胞合成卵黄原蛋白。这些实验的扩展不仅将使对卵黄原蛋白多基因家族激活的更精确分析成为可能，还将为类固醇激素受体在调节基因表达中所起的作用提供直接的功能证据。
