title: Zygotic Genome Activation Revisited: Looking Through the Expression and Function of Zscan4.
abstract: Zygotic genome activation (ZGA, a.k.a. zygotic gene activation) is a critical event in development, when the paternally derived genome and maternally derived genome begin to be activated and transcribed after fertilization. Major ZGA occurs at the two-cell stage in mice and the four- to eight-cell stage in human preimplantation embryos. It has been thought that ZGA exists to provide RNAs and proteins supporting embryonic development after supplies stored in oocytes are used up; however, this paradigm does not seem to explain recent findings. For example, many ZGA genes-once activated-are quickly turned off, and thus ZGA forms a transient wave of transcriptional activation. In addition, ZGA genes are not evolutionarily conserved. In this review, we address these issues by focusing on Zscan4 (zinc finger and SCAN domain-containing 4), which was identified for its specific expression in preimplantation embryos during ZGA. Detailed molecular analyses of Zscan4 expression and function have revealed common features of Zscan4-associated events (Z4 events) in mouse embryonic stem cells and ZGA in preimplantation embryos. One feature is a rapid derepression and rerepression of constitutive heterochromatin, which includes pericentromeric major satellites and telomeres, and facultative heterochromatin, which includes retrotransposons and Z4 event-associated genes. We propose that the Z4 event superimposed on ZGA plays a critical role in the maintenance of genome and chromosome integrity in preimplantation embryos by promoting correction of DNA damage and chromosome abnormalities.
authors.affiliation: Keio University School of Medicine, Tokyo, Japan. Electronic address: ko.minoru@keio.jp.
authors.forename: M S H
authors.initials: MS
authors.lastname: Ko
mesh_terms: D000818:Animals; D004249:DNA Damage; D019143:Evolution, Molecular; D018507:Gene Expression Regulation, Developmental; D016678:Genome; D006801:Humans; D014157:Transcription Factors / Q000378:metabolism*; D015053:Zygote / Q000378:metabolism*
chemical_list: D014157:Transcription Factors
keywords: Chromosome abnormality; DNA damage; Heterochromatin; Preimplantation embryos; Zscan4; Zygotic gene activation; Zygotic genome activation