Regulation of Transcriptional Activity during the First and Second Cell Cycles in the Preimplantation Mouse Embryo

Abstract

Transcription of endogenous genes in preimplantation 1- and 2-cell mouse embryos was determined by monitoring the incorporation of BrUTP by plasma membrane-permeabilized embryos. Incorporation is observed starting by mid-S phase in the 1-cell embryo and increases progressively; the amount of incorporation by the 1-cell embryo in G2 is about 20% that of the 2-cell embryo in G2. Incorporation by the male pronucleus is always about four to five times greater than that of the female pronucleus. Nevertheless, the amount of incorporation by the female pronucleus present in parthogenetically activated eggs is similar to the total amount of incorporation in inseminated eggs, i.e., the transcriptional capacity of the female pronucleus is not inherently less than that of the male pronucleus. Inhibiting the first round of DNA replication does not prevent the initiation of transcription in the 1-cell embryo, but does inhibit the extent of BrUTP incorporation by 35%. The transcriptional machinery of the 1-cell embryo appears to be rate-limiting, since the total amount of BrUTP incorporation by parthenogenetically activated and dispermic eggs is similar to that in monospermic eggs; trispermic eggs incorporate BrUTP to only about 60% the level of monospermic eggs. A transcriptionally repressive state may start to develop in the 2-cell embryo, since inhibiting the second round of DNA replication results in an 50% increase in BrUTP incorporation. Trapoxin treatment, which induces histone hyperacetylation, enhances incorporation by 2-cell embryos 1.8-fold and suggests that histone hyperacetylation can relieve this repression.

Transcriptional activation of transposable elements in mouse zygotes is independent of Tet3-mediated 5-methylcytosine oxidation

“…We also validated the BrUTP antibody specificity by substituting BrUTP with UTP ( Figure 4A). Consistent with previous reports [27,28], global transcriptional activity of the paternal genome, which is marked by lack of H3K9me2 staining, is significantly higher than that of the maternal genome ( Figure 4A). …”

“…RT-qPCR analysis confirmed that the expression dynamics of major satellite DNA and Tet3 previously shown to be unregulated at the 1-cell stage are consistent with previous results [10,29]. This result indicates that some TEs are activated in the 1-cell embryos when global transcription is also initiated [27,28]. The asymmetric nature of 5mC oxidation in zygotes prompted us to ask whether activation of the TEs in zygotes exhibits allele specificity.…”

“…Zygotic gene activation, the earliest expression from zygote genome after fertilization, begins at the middle of 1-cell stage [27,28]. To test whether Tet3-mediated 5mC oxidation is involved in zygotic gene activation, we analyzed de novo RNA synthesis by measuring incorporation of 5-bromouridine-5′-triphosphate (BrUTP).…”

HDAC1 and HDAC2 in mouse oocytes and preimplantation embryos: Specificity versus compensation

“…40 HDACs likely underlie development of the transcriptionally repressive state because inducing histone hyperacetylation using HDAC inhibitors not only relieves the enhancer requirement for efficient expression of plasmid-borne reporter genes in 2-cell embryos, 83,84 but also results in a further increase in global transcription. 85 Several lines of evidence support a role for HDAC1 in development of a transcriptionally repressive state that initiates in 2-cell embryos. 42 First, microarray data and qRT-PCR show that Hdac1 is zygotically expressed beginning from 2-cell stage, 42,86,87 accompanying genome activation.…”

Characterization of non-canonical Polycomb Repressive Complex 1 subunits during early mouse embryogenesis

“…Firstly, PRC1.6 is the only PRC1 complex that, in addition to catalytic activity toward H2AK119, possesses histone deacetylation activity 13 and, therefore, could also contribute to the rapid changes in histone acetylation that characterize pre-implantation development. 1,2,4 Secondly, PRC1.6 contains a recognition module, through L3MBTL2, for H4K20me1, which is essential for pre-implantation development, as deletion of PR-Set7 results in lethality by the 8-cell stage, in a manner dependent of its methyltransferase activity. 13,21 Since L3MBTL2 is a defining, unique feature of PRC1.6, we therefore assessed its localization through preimplantation development.…”