The role of DUX4 in the early human embryo
Aug. 23, 2019 14:00 - 15:00
DB Bldg. SeminarRoom A7F
Karolinska Institutet, Sweden
Human embryo development starts after the fertilization of the oocyte with a rapid succession of parallel processes, each critical for the progression of development. The earliest alterations in the transcriptome include the rapid but transient appearance of transcripts of the DUX4 repeat sequence gene in the zygotes, but not oocytes; the fourfold degradation of a large number of oocyte-specific mRNAs until the 4-cell stage; and the early embryo genome activation (EGA) at the 4-cell stage, involving the significant accumulation of 32 mRNAs, followed by 129 additional genes at the 8-cell stage (1,2).
Following up on our earlier studies to understand human EGA by performing single-cell transcriptome sequencing of over 340 cells, including oocytes, zyogtes and single blastomeres from 4-cell and 8-cell embryos (1), we have now focused on understanding the role of DUX4 in regulating the transition from the oocyte to totipotent blastomeres (3). We verified the presence of DUX4 transcripts in zygotes and cleavage embryos from different data sources and a quantitative ligation method. We used DUX4-specific antibodies to verify the appearance, location, and disappearance of DUX4 protein. We modelled DNA-bound and unbound DUX4 protein structures. We assessed also DUX4 protein-protein interactions using the MAC-TAG method (4). Using siRNA, we downregulated DUX4 in human zygotes and observed the consequences of DUX4 dysregulation on subsequent cell divisions and the transcriptome. Using a human embryonic stem cell (hESC) model, we assessed DUX4 effects on the chromatin and transcriptome (3).
Our findings indicate that the DUX4 protein localizes in zygotes and 2- and 4-cell blastomeres in the cytoplasm and nuclei. At the 8-cell stage, virtually no DUX4 protein remains in cells. Downregulation of DUX4 in zygotes does not affect cell divisions, but the analysis of the transcriptomes of blastomeres indicates delayed oocyte mRNA degradation. The DUX4 protein interacts with several major chromatin and transcription regulators. In the hESC model, DUX4 exerts a major effect on the opening of chromatin.
Our results reveal multiple roles for DUX4 in early human development, including regulation of the chromatin, transcription and reprogramming the oocyte transcriptome.