Induction of Early Transcription in One-Cell Mouse Embryos by Microinjection of the Nonhistone Chromosomal Protein HMG-I

Abstract

In the mouse embryo, the onset of zygotic transcription occurs at the end of the first cell cycle, upon completion of DNA replication. We show that the nonhistone chromosomal protein HMG-I, whose translocation into the pronuclei of one-cell embryos is linked to this first round of DNA synthesis, plays a critical role in the activation of zygotic transcription. Indeed, microinjection of purified HMG-I results in a higher nuclear accumulation of the protein and triggers an earlier activation of zygotic transcription, an effect which is abolished by the preincubation of the protein with a specific antibody directed against its AT-hook DNA-binding motifs. Significantly, microinjection of this antibody also prevents the normal onset of transcription in the embryo, suggesting that endogenous HMG-I is similarly involved in this process. Finally, microinjection of the exogenous protein modifies chromatin structure as measured by in situ accessibility to DNase I. We propose that general chromosomal architectural factors such as HMG-I can modulate the accessibility of chromatin to specialized regulatory factors, thereby promoting a transcriptionally competent state.

The expression of HMGA genes is regulated by their 3′UTR

“…For example, the onset of transcription in one-cell mouse embryos depends on the amount of HMGA1a, probably due to a competitive displacement of histone H1 or other general repressors, making chromatin regions accessible to the transcription machinery (Beaujean et al, 2000). In addition, only transgenic mice expressing high levels of truncated HMGA2 lacking the acidic C-tail showed an increased adiposity and a giant phenotype (Battista et al, 1999).…”

Nuclear Translocation of a Pre-mRNA Splicing Factor, p100prp1/zer1/prp6, in Mouse 1-cell Embryos.

“…The nuclear translocation of p100 prp1/zer1/prp6 seems to be closely linked to the onset of the minor ZGA which occurs at the late 1-cell stage. It has been reported that the nuclear concentrations of SP1, TBP [8], HMG-1 [10], RPB1 [9], and snRNPs [17] in mouse 1-cell embryos also increase during the 1-cell stage. It has been antibody.…”

“…During the transcriptionally inactive period, the subcellular distribution of a number of nuclear proteins shifts from the cytoplasm to the nucleus of 1-cell embryos, and this nuclear translocation is correlated closely with the onset of embryonic transcription. Nuclear accumulation of general transcription factors, Sp-1 and the TATA box binding protein (TBP), the high-mobility group I non-histone chromosomal proteins (HMGI), and the largest subunit of RNA polymerase II (RPB1) occurs during the first cell cycle of 1-cell embryos [8][9][10]. We found recently that nuclear factor kappa B (NF-kB), a transcription factor, is transiently localized in the pronucleus of the mouse embryo at the early 1-cell stage and is exported to the cytoplasm as the 1-cell stage progresses [11].…”

Establishment of customized mouse stem cell lines by sequential nuclear transfer

“…Cultured confluent ES cells were fixed with formalin for 15 min before ALP staining as described with 100 mM Tris-Hcl (pH 9.5) plus NBT (Sigma No.N-5514) and BCIP (Sigma No.B-0274) [24,25]. Immunostaining was performed with the following monoclonal antibodies: SSEA-1 (Chemicon, No.…”