Repressive Roles of Erf and Elk in FGF-Regulated Neural Development in Ciona intestinalis

Insights from urochordates/tunicates can instruct on the evolutionary origins of key cell types or gene regulatory mechanisms such as for the ‘new head’ sensory placodes and neural crest. Taking advantage of their invariant lineage with reproducible binary cell fate switches, we decipher in Ciona intestinalis the unanswered question of how highly conserved and ongoing FGF/MAPK/ERK signalling gives rise to co-existing nuclear Ets activation and repression states to finely tune the neural fate and its diversification. Genetic interference shows that Erf and Elk repressors play successive roles at different transcriptional targets. We propose an Ets site occupancy model where activators and repressors compete to produce consecutive and opposite winning switches in adjacent territories. Such Ets factor network is relevant beyond the ascidian neuroectodermal lineage to produce palp placodal and neural plate progenitors. It may explain Ets factor effects in many metazoans including Elk in vertebrate neural crest and appeal to stem cell and cancer research.