Hake, SandraPullamsetti, SoniLüttmann, Felipe FranciscoFelipe FranciscoLüttmann2025-02-122025-02-122023https://jlupub.ub.uni-giessen.de/handle/jlupub/20243https://doi.org/10.22029/jlupub-19598The preimplantation stage is the first phase in mammalian development and starts with fusion of egg and sperm. Thereby, fertilization gives rise to a totipotent single cell, called zygote, which holds the capacity to develop into an entire new organism. Within the zygote, the parental chromatin is reprogrammed to form a new embryonic genome. Activation of this genome results in the first transcriptional event in life, called zygotic genome activation (ZGA). In mice, this transcriptional burst occurs at the 2-cell stage and results in transient upregulation of thousands of genes. Immediately afterwards, at the 4-cell stage, those genes become silenced. Even though ZGA was discovered decades ago, its regulation remains poorly understood. Recently, the double homeobox transcription factor Dux was shown to drive a 2- cell-like conversion of pluripotent embryonic stem cells. In these cells, ectopic expression of Dux induces opening of ZGA-associated gene loci and consequent transcription of encoded genes. Thereby, Dux was discovered as a driver of ZGA. However, genetic depletion of Dux results in negligible impairment of ZGA and is compatible with development. Nevertheless, both activation and rapid decommissioning of the 2-cell-specific transcriptional profile are essential for life. However, how this is regulated has remained unknown. In this thesis, I investigated a potential role for another member of the DUX transcription factor family called Duxbl. Transcriptional profiling of developing murine embryos revealed that Duxbl is part of the ZGA-expression panel. In contrast to Dux, Duxbl does not interact with a histone acetyl transferase and does not induce expression of ZGA-associated genes when overexpressed in embryonic stem cells. Instead, Duxbl suppresses Dux-induced upregulation of 2-cell specific transcripts in vitro. Mechanistically, conservation of the DNA-binding domains of Duxbl and Dux is associated with occupation of Dux-binding sites by Duxbl within ZGA-promoters. Accordingly, preponed Duxbl expression in mouse embryos suppressed a large portion of ZGA- genes and resulted in a 2-cell stage developmental arrest. Inversely, inactivation of Duxbl led to upregulation of ZGA-associated transcripts and a developmental block at the 2- to 4-cell stage. This study identifies Duxbl as a master regulator in preimplantation development that is necessary for decommissioning the totipotency-associated ZGA-burst and thereby enabling the first cell fate decisions.enIn Copyrightddc:570