ERK signaling dissolves ERF Repression Condensates in Living Embryos

Abstract

Phase separation underlies the organization of the nucleus, including the biogenesis of nucleoli and the packaging of heterochromatin. Here we explore the regulation of transcription factor condensates involved in gene repression by ERK signaling in gastrulating embryos of a simple proto-vertebrate (Ciona). ERK signaling induces nuclear export of the transcriptional repressor ERF, which has been linked to various human developmental disorders. Using high resolution imaging we show that ERF is localized within discrete nuclear condensates that dissolve upon ERK activation. Interestingly, we observe dynamic pulses of assembly and dissociation during the cell cycle, providing the first visualization of a nuclear phase separation process that is regulated by cell signaling. We discuss the implications of these observations for producing sharp on/off switches in gene activity and suppressing noise in cell-cell signaling events.

Model of neural induction in the ascidian embryo

“…In contrast, the transcription of the immediate-early gene Otx is bimodal, with a ON response that is restricted to neural precursors. We hypothesized that the ON/OFF response is, at least in part, due to the dual control of Otx expression (Williaume et al, 2021): ETS1/2 phosphorylation by ERK is required for its transcriptional activator activity (Weaver et al, 2022), while phosphorylation of the ERF2 repressor by dpERK promotes its nuclear export, thus preventing its binding to DNA (Le Gallic et al, 1999;2004) (Fig. 1A).…”

“…The Ets2 repressor factor 2 (ERF2) (Yagi et al, 2003) recognizes the same binding site as the transcriptional activator ETS1/2 and its activity is negatively controlled by ERK via nuclear export (Le Gallic et al, 1999;2004;and Weaver et al, 2022). Thus, we considered that Otx expression is enhanced by the stimulation of an activator (A; e.g.…”

An FGF Timer for Zygotic Genome Activation

“…ERF was also shown to repress Otx in Ciona embryos at the 32-cell stage (Williaume et al 2021). Interestingly, we previously observed that ERF condensates were able to dissolve and reform within a single interphase (Weaver et al 2022), suggesting a dynamic response to endogenous FGF signals.…”

“…We previously determined that ERF undergoes phase separation in response to FGF signaling. When FGF is active, ERF is phosphorylated, causing condensates to dissolve, coinciding with derepression of target genes (Weaver et al 2022). ERF was also shown to repress Otx in Ciona embryos at the 32-cell stage (Williaume et al 2021).…”