Sarkar P K, Moscona A A
Differentiation. 1977 Jan 14;7(2):75-82. doi: 10.1111/j.1432-0436.1977.tb01499.x.
In the neural retina of the chick embryo, hydrocortisone (HC) elicits differential gene expression resulting in the induction of glutamine synthetase (GS), which is an enzyme marker of differentiation in the retina. The relationship between nuclear binding of receptor-hydrocortisone (R-HC) complexes and GS induction was investigated in cultures of retina tissue from 12-day chick embryos. The number of HC binding sites in the cytoplasm was estimated as 1650+/-200 per retina cell; there are approximately 1500+/-100 acceptor sites for R-HC per retina nucleus. GS induction in the retina became detectable only after R-HC bound to more than 40% of the nuclear acceptors sites; increased binding coincided with higher induction levels, until complete site saturation was attained; Proflavine, which blocks preferentially and completely GS induction in the retina by interfering in the nucleus with the enzyme-inducing action of the hormone, reduced nuclear binding of R-HC by only 20%; thus, only part of the R-HC that binds in the nucleus appears to be directly involved in eliciting the induction of GS. Within one hour after exposure of the retina to an inducing dose of HC, there was translocation of HC and HC-receptors (as R-HC complexes) from the cytoplasm into the nucleus and saturation of nuclear accepegan to decline; in 12 h, it was reduced to 50% of the initial saturation level. Since, during this time, the enzyme activity to increase, persistence of the induced state depends on association of the hormone with only a portion of the sites in the nucleus to which it can bind. The decrease in the amount of bound HC in the nuclei of induced cells was accompanied by an increase in the level of HC receptors in the cytoplasm. About 50% of this increase could be prevented by cycloheximide; this suggests that the reappearance of HC receptors in the cell cytoplasm may be due, at least in part, to de novo synthesis of HC receptors.
在鸡胚的神经视网膜中，氢化可的松（HC）引发差异基因表达，导致谷氨酰胺合成酶（GS）的诱导，GS是视网膜分化的一种酶标志物。在12日龄鸡胚的视网膜组织培养物中，研究了受体 - 氢化可的松（R - HC）复合物的核结合与GS诱导之间的关系。视网膜细胞质中HC结合位点的数量估计为每个视网膜细胞1650±200个；每个视网膜细胞核中R - HC的受体位点约有1500±100个。只有当R - HC与超过40%的核受体位点结合后，视网膜中的GS诱导才变得可检测到；结合增加与更高的诱导水平一致，直到达到完全位点饱和；原黄素通过在细胞核中干扰激素的酶诱导作用，优先且完全阻断视网膜中的GS诱导，仅使R - HC的核结合减少20%；因此，在细胞核中结合的R - HC只有一部分似乎直接参与引发GS的诱导。在视网膜暴露于诱导剂量的HC后一小时内，HC和HC受体（作为R - HC复合物）从细胞质转移到细胞核，核受体饱和并下降；在12小时内，它降至初始饱和水平的50%。由于在此期间酶活性增加，诱导状态的持续取决于激素与它可以结合的细胞核中仅一部分位点的结合。诱导细胞的细胞核中结合的HC量的减少伴随着细胞质中HC受体水平的增加。约50%的这种增加可以被放线菌酮阻止；这表明细胞质中HC受体的重新出现可能至少部分归因于HC受体的从头合成。
