Prioleau M N, Buckle R S, Méchali M
Institut Jacques Monod, Molecular Embryology Unit, Paris, France.
EMBO J. 1995 Oct 16;14(20):5073-84. doi: 10.1002/j.1460-2075.1995.tb00189.x.
The determination of chromatin for transcription during early development as well as the requirement for trans-acting factors during this period has been analysed in Xenopus. Basal transcription is repressed both during oogenesis and after the mid-blastula transition (MBT), and transactivators are required to relieve this repression. In contrast, transactivators cannot overcome the generalized transcriptional repression which occurs in embryos before MBT. However, they do bind to promoters leading to a repressed but preset chromatin structure. Experiments involving the pre-binding of TATA binding protein (TBP) or of the strong transactivator GAL4-VP16 further show that there is no limiting factor before the MBT, and that it is the recruitment and stabilization of the basal transcription machinery and not of transactivators which is repressed during early development. This multi-step process in gene activation, with activation of promoters temporally uncoupled from their commitment, may be of importance in the regulation of early embryonic events by providing molecular signposts for future determinations.
在非洲爪蟾中，已对早期发育过程中转录染色质的确定以及这一时期反式作用因子的需求进行了分析。基础转录在卵子发生过程中以及囊胚中期转换（MBT）之后均受到抑制，并且需要反式激活因子来解除这种抑制。相反，反式激活因子无法克服在MBT之前胚胎中发生的普遍转录抑制。然而，它们确实会与启动子结合，导致染色质结构被抑制但已预设。涉及TATA结合蛋白（TBP）或强反式激活因子GAL4-VP16预结合的实验进一步表明，在MBT之前不存在限制因子，并且在早期发育过程中受到抑制的是基础转录机制的募集和稳定，而非反式激活因子。基因激活中的这一多步骤过程，即启动子的激活在时间上与其确定过程解偶联，可能通过为未来的决定提供分子路标，在早期胚胎事件的调控中具有重要意义。
