Zygotic genome activation in the chicken: a comparative review
Maternal RNAs and proteins in the oocyte contribute to early embryonic development. After fertilization, these maternal factors are cleared and embryonic development is determined by an individual’s own RNAs and proteins, in a process called the maternal-to-zygotic transition. Zygotic transcription is initially inactive, but is eventually activated by maternal transcription factors. The timing and molecular mechanisms involved in zygotic genome activation (ZGA) have been well-described in many species. Among birds, a transcriptome-based understanding of ZGA has only been explored in chickens by RNA sequencing of intrauterine embryos. RNA sequencing of chicken intrauterine embryos, including oocytes, zygotes, and Eyal-Giladi and Kochav (EGK) stages I–X has enabled the identification of differentially expressed genes between consecutive stages. These studies have revealed that there are two waves of ZGA: a minor wave at the one-cell stage (shortly after fertilization) and a major wave between EGK.III and EGK.VI (during cellularization). In the chicken, the maternal genome is activated during minor ZGA and the paternal genome is quiescent until major ZGA to avoid transcription from supernumerary sperm nuclei. In this review, we provide a detailed overview of events in intrauterine embryonic development in birds (and particularly in chickens), as well as a transcriptome-based analysis of ZGA.
KeywordsAvian species Genome activation Intrauterine embryos Maternal-to-zygotic transition
This work was supported by the National Research Foundation of Korea (NRF) Grant 2015 R1A3A2033826 (Ministry of Science, Information and Communication Technology, and Future Planning; MSIP) and the Cooperative Research Program for Agriculture Science and Technology Development (Project PJ0144612019) from the Korean Rural Development Administration.
The study was designed by DR and JYH. The manuscript was drafted by DR and YSH. The content in the manuscript was critically checked by HCL and JYH. All the authors checked and gave their approval of this version to be published.
Compliance with ethical standards
Conflict of interest
All the authors declare that they have no competing interests.
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