Abstract
Transposable elements (TEs) are powerful cis-regulatory drivers of gene expression, particularly during early development when many TEs become de-repressed. MERVL elements are transiently up-regulated in mouse totipotent two-cell (2C) embryos during major zygotic genome activation (ZGA) and 2C-like cells in vitro. One of the most powerful activators of MERVL is the pioneer transcription factor, Dux. However, apparent differences lie in the requirement for Dux versus MERVL activation in embryos. Moreover, sustained Dux activation causes cell toxicity, which may or may not be linked to MERVL. Using a CRISPR activation system, we unpick the relative role of Dux and MERVL in ZGA, totipotent-like characteristics, and cell toxicity. We find that MERVL activation drives a portion of the Dux-dependent transcriptome, sufficient for expanded fate potential, but not other totipotency features. Conversely, Dux-induced pathology is independent of MERVL activation and involves the proapoptotic factor, Noxa. Our study highlights the complexity of the Dux-MERVL transcriptional network and uncovers a previously unknown player in Dux-driven pathology.