Wakefield L, Gurdon J B
MRC Laboratory of Molecular Biology, Cambridge, UK.
EMBO J. 1983;2(9):1613-9. doi: 10.1002/j.1460-2075.1983.tb01632.x.
In the normal development of Xenopus laevis, genes for oocyte-type and somatic-type 5S RNAs are both expressed in late blastulae. Estimates of rates of synthesis indicate that the oocyte-type genes (5Sooc) undergo at least a 100-fold reduction in transcriptional activity between the end of oogenesis and the late blastula stage, and at least a further 20-fold reduction during gastrulation. When neurula nuclei, with inactive 5Sooc genes, were transplanted to enucleated eggs, the resulting nuclear-transplant embryos showed a reactivation of 5Sooc genes in blastulae and a subsequent inactivation after this stage. This effect is not explicable by a differential stability of the two types of 5S RNA. We conclude that egg or early embryo cytoplasm must contain components which can continuously regulate 5S gene expression, and that the mechanism by which 5Sooc genes are developmentally inactivated does not persist through mitosis in early embryos. These results have been obtained by a new procedure in which oocyte- and somatic-type 5S RNAs are separated in a 4 M urea-15% acrylamide gel.
在非洲爪蟾的正常发育过程中，卵母细胞型和体细胞型5S RNA的基因在囊胚后期均有表达。合成速率的估计表明，卵母细胞型基因（5Sooc）在卵子发生结束至囊胚后期之间转录活性至少降低100倍，在原肠胚形成期间至少再降低20倍。当具有无活性5Sooc基因的神经胚细胞核被移植到去核卵中时，产生的核移植胚胎在囊胚期显示5Sooc基因重新激活，在此阶段之后随后失活。这种效应不能用两种类型5S RNA的差异稳定性来解释。我们得出结论，卵或早期胚胎细胞质中必须含有能够持续调节5S基因表达的成分，并且5Sooc基因在发育过程中失活的机制在早期胚胎的有丝分裂过程中不会持续存在。这些结果是通过一种新方法获得的，其中卵母细胞型和体细胞型5S RNA在4M尿素-15%丙烯酰胺凝胶中分离。
