Dr. Daria Onichtchouk (CIBSS AI), Institute of Biology I, University of Freiburg
Awakening of zygotic transcription at zygotic genome activation (ZGA) in zebrafish embryos relies on homologs of mammalian pluripotency transcription factors (TFs), Pou5f3, Sox19b and Nanog. Pluripotency TFs promote chromatin accessibility on enhancers, priming the earliest expressed genes in zebrafish embryos. Strikingly, loss of pluripotency TFs resulted in dramatically altered signalling landscape in the embryo and in premature activation of dormant regulatory programs, involved in regulation of organogenesis and differentiation. In zebrafish, germ layer specification depends on the dorsal pole of maternal β-catenin activity, and the release of Nodal signals from the yolk syncytial layer (YSL). In response to these signals, the initially pluripotent deep cells become specified as axial mesoderm (Spemann Organizer), other mesendoderm and ectoderm progenitors. It is not yet clear how Pou5f3, Sox19b and Nanog attenuate the response of the embryonic cells to these graded and dynamically changing embryonic signals. We will address this question by combining ex vivo approach (embryotypic cultures, exposed to the exogenous signals with the defined range) with single cell multi-omics in the context of whole wild-type and mutant embryos.