Pluripotency factors determine gene expression repertoire at zygotic genome activation.

Awakening of zygotic transcription in animal embryos relies on maternal pioneer transcription factors. The interplay of global and specific functions of these proteins remains poorly understood. Here, we analyze chromatin accessibility and time-resolved transcription in single and double mutant zebrafish embryos lacking pluripotency factors Pou5f3 and Sox19b.

Maternal Nanog is required for zebrafish embryo architecture and for cell viability during gastrulation.

Nanog has been implicated in establishment of pluripotency in mammals and in zygotic genome activation in zebrafish. In this study, we characterize the development of MZ (maternal and zygotic null) mutant zebrafish embryos Without functional Nanog, epiboly is severely affected, embryo axes do not form and massive cell death starts at the end of gastrulation. We show that three independent defects in MZ mutants contribute to epiboly failure: yolk microtubule organization required for epiboly is abnormal, maternal mRNA fails to degrade owing to the absence of miR-430, and actin structure of the yolk syncytial layer does not form properly.