Deposition of acetylated histones by RNAP II promoter clearance may occur at onset of zygotic gene activation in preimplantation mouse embryos.
We investigated the contribution of phosphorylated RNA polymerase II (RNAP II) and dynamic epigenetic changes to the onset of minor zygotic gene activation (ZGA). Using immunofluorescence staining, we observed that the nuclear localization of RNAP II was initiated by 6 hours post insemination (hpi), whereas RNAP II phosphorylated at serine residue 5 of the carboxyl-terminal domain (CTD) was localized by 9 hpi, and then RNAP II phosphorylated at serine residue 2 of the CTD was localized in the nucleus of embryos by 12 hpi. In a transient gene expression assay using a plasmid reporter gene (pβ-actin/luciferase+/SV40) injected during 6-9 hpi into the male pronucleus, the luciferase+ gene was actively transcribed and translated by 13 and 15 hpi, respectively, indicating that a transcriptionally silent state persisted for at least 4 hours after injection. We found that the methylation status in the chicken β-actin promoter region of the plasmid reporter gene may not be associated with the transcriptionally silent state before minor ZGA. Exposure to trichostatin A did not induce premature expression of the silent reporter gene injected into 1-cell embryos containing histone deacetylase activity and did not affect the amount of luciferase produced per embryo. Acetylated histone H3 lysine 9/14 and acetylated histone H4 lysine 12 and 16 were enriched preferentially in the injected reporter gene at least until 13 hpi, which coincided with the transcriptionally active state. Taken together, these results suggest that deposition of selectively acetylated histones onto the chromatin of 1-cell embryos functions together with transcriptional elongation by RNAP II and that this sequential chromatin remodeling is involved in the molecular mechanism associated with the onset of minor ZGA in the preimplantation mouse embryo.
Tokoro
Mikiko
M
Division of Biological Science, Graduate School of Biology-Oriented Science and Technology, Kinki University, Wakayama, Japan.
Shin
Seung-Wook
SW
Nishikawa
Satoshi
S
Lee
Hyang-Heun
HH
Hatanaka
Yuki
Y
Amano
Tomoko
T
Mitani
Tasuku
T
Kato
Hiromi
H
Anzai
Masayuki
M
Kishigami
Satoshi
S
Saeki
Kazuhiro
K
Hosoi
Yoshihiko
Y
Iritani
Akira
A
Matsumoto
Kazuya
K
D000107:Acetylation / Q000187:drug effects; D000818:Animals; D001755:Blastocyst / Q000378:metabolism*; D044127:Epigenesis, Genetic / Q000187:drug effects; D005260:Female; D017930:Genes, Reporter / Q000187:drug effects; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology; D006657:Histones / Q000378:metabolism*; D006877:Hydroxamic Acids / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000187:drug effects; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D012319:RNA Polymerase II / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects; D015053:Zygote / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
D056572:Histone Deacetylase Inhibitors; D006657:Histones; D006877:Hydroxamic Acids; D021122:Protein Subunits; C012589:trichostatin A; D012319:RNA Polymerase II