CONSTRAINTS ON TRANSCRIPTIONAL ACTIVATOR FUNCTION CONTRIBUTE TO TRANSCRIPTIONAL QUIESCENCE DURING EARLY XENOPUS EMBRYOGENESIS
CONSTRAINTS ON TRANSCRIPTIONAL ACTIVATOR FUNCTION CONTRIBUTE TO TRANSCRIPTIONAL QUIESCENCE DURING EARLY XENOPUS EMBRYOGENESIS
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DOI：
10.1002/j.1460-2075.1995.tb07164.x
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发表时间：
1995-04-18
期刊：
影响因子：
11.4
通讯作者：
WOLFFE, AP
中科院分区：
文献类型：
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作者：
ALMOUZNI, G;WOLFFE, AP
我们研究了非洲爪蟾中囊胚转变（MBT）之前转录静止的原因。我们发现 II 类和 III 类基因的转录有不同的要求。人工增加胚胎中的 DNA 数量使其超过 MBT 中的 DNA 数量，可以使 tRNA 基因提前转录，但不能使腺病毒 E4 或人类巨细胞病毒 (CMV) 启动子提前转录。因此，外源 DNA 抑制剂的滴定决定了 III 类基因的激活，但不能确定 II 类基因的激活。我们证明抑制剂的作用取决于核心组蛋白与 DNA 的结合。添加外源 TBP 以及胚胎内 DNA 量的增加，可以在 MBT 之前实现 II 类基因的显着基础转录，但不会增加 tRNA 基因的转录。为了检查高于基础水平的转录激活情况，我们使用了包含五个 Gal4 结合位点的确定最小启动子和激活剂 Gal4-VP16。早熟转录激活是在 MBT 之前由 Gal4-VP16 指导的，这表明在这个早期发育阶段存在功能性转录机制。此外，由于这种激活可以在没有外源 TBP 或染色质滴定的情况下发生，因此可以穿透染色质的转录因子足以将该机制招募到启动子上。我们的结果支持这样的假设：非洲爪蟾早期胚胎发生过程中转录的时间调节不仅反映了 DNA 抑制剂的滴定，而且反映了 MBT 之前转录激活剂活性的缺乏。
We have examined the cause of transcriptional quiescence prior to the mid-blastula transition (MBT) in Xenopus laevis. We have found distinct requirements for transcription of class II and class III genes. An artificial increase of the amount of DNA present within the embryo over that found at the MBT allows precocious transcription of tRNA genes, but not of the adenovirus E4 or human cytomegalovirus (CMV) promoters. Thus titration of an inhibitor by exogenous DNA determines class III but not class II gene activation. We demonstrate that the action of the inhibitor depends on the association of core histones with DNA. The addition of exogenous TBP, together with an increase in the amount of DNA within the embryo, allows significant basal transcription of class II genes prior to the MBT, whereas it does not increase transcription of tRNA genes. To examine the activation of transcription above basal levels, we used a defined minimal promoter containing five Gal4 binding sites and the activator Gal4-VP16. Precocious transcriptional activation is directed by Gal4-VP16 prior to the MBT, demonstrating that a functional transcriptional machinery exists at this early developmental stage. Furthermore, since this activation can occur in the absence of exogenous TBP or chromatin titration, a transcription factor that can penetrate chromatin is sufficient for recruitment of this machinery to a promoter. Our results support the hypothesis that the temporal regulation of transcription during early embryogenesis in Xenopus reflects not only a titration of inhibitors by DNA, but also a deficiency in the activity of transcriptional activators prior to the MBT.