Programming of a repressed but committed chromatin structure during early development.

Abstract

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.

A functional analysis of p53 during early development of xenopus laevis

“…During this stage, the nuclear envelope is disrupted and p53 can thus access chromatin. Transcriptional repression during early development is mainly due to a dynamic competition between the histones massively present in the egg, and which dominantly repress the assembly of transcription complexes (Prioleau et al, 1994(Prioleau et al, , 1995. This repression phenomenon a ects all types of promoters.…”

“…25 nl of injection mix was injected into germinal vesicles as previously described (Prioleau et al, 1995). Seventeen to 30 oocytes were injected per experimental point.…”

MiRNA expression analysis during normal zebrafish development and following inhibition of the Hedgehog and Notch signaling pathways

“…It is possible that a narrow window exists at exactly the midbastula transition when many genes are initially transcribed even if they then become downregulated until later development. Previous work has suggested that assembly of chromatin versus association of the basal transcription machinery limits transcription prior to the midbastula transition but that specific transcription activators can still access the DNA before this time (Prioleau, 1995). After the midblastula transition, the basal transcription machinery joins to activate transcription but subsequent production of other regulators could then establish developmentally regulated transcriptional programs.…”

Translation of Maternal TATA-Binding Protein mRNA Potentiates Basal but Not Activated Transcription in Xenopus Embryos at the Midblastula Transition

“…TATA-binding protein (TBP) has been identified as a molecule that is able to facilitate transcription before the MBT if two conditions are met (3,37,38): (i) recombinant TBP protein is preincubated with the promoter template prior to injection into embryos, and (ii) a state of incomplete chromatin assembly is present. Such an immature chromatin structure is observed at early time points after injection of a promoter template and after coinjection of a large amount of nonspecific DNA that titrates chromatin assembly.…”