A stress-responsive p38 signaling axis in choanoflagellates

Animal kinases regulate cellular responses to environmental stimuli, including cell differentiation, migration, survival, and response to stress, but the ancestry of these functions is poorly understood. Choanoflagellates, the closest living relatives of animals, encode homologs of diverse animal kinases and have emerged as model organisms for reconstructing animal origins. However, efforts to study kinase signaling in choanoflagellates have been constrained by the limitations of currently available genetic tools. Here we demonstrate that small molecule approaches provide a complementary and scalable approach for studying kinase function in choanoflagellates. To study the physiological roles of choanoflagellate kinases, we established two high-throughput platforms to screen the model choanoflagellateSalpingoeca rosettawith a curated library of human kinase inhibitors. We identified 95 diverse kinase inhibitors that disruptS. rosettacell proliferation. By exploring structure-activity relationships of one inhibitor, sorafenib, we identified a p38 kinase as a regulator of heat and oxidative stress inS. rosetta. This finding indicates a conserved p38 function between choanoflagellates, animals, and fungi. Moreover, this study demonstrates that existing kinase inhibitors can serve as powerful tools to examine the ancestral roles of kinases that regulate modern animal development.