A small molecule screen reveals the essentiality of p38 kinase for choanoflagellate cell proliferation

Abstract

AbstractChoanoflagellates, the closest living relatives of animals, express diverse animal genes and may thereby provide insights into the ancestral roles of genes essential for modern animal cell biology and development. While efforts to study conserved gene families in choanoflagellates have been constrained by the relative inefficiency of currently available genetic tools, small molecule approaches are readily available and may provide a complementary and scalable approach for studying protein function. To study the physiological roles of choanoflagellate kinases, including animal kinase homologs, we established a high-throughput platform to screen the model choanoflagellate Salpingoeca rosetta with a curated library of human kinase inhibitors. We identified 36 diverse kinase inhibitors that disrupt S. rosetta cell proliferation. By exploring structure-activity relationships of one inhibitor, sorafenib, we identified a p38 kinase as a stress-activated regulator of cell proliferation in S. 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.Significance StatementChoanoflagellates are the closest living relatives of animals and are useful models for studying the ancestral functions of animal gene families, including kinases. In this study, we treated choanoflagellates with a library of small molecules to determine if currently available human kinase inhibitors could reveal choanoflagellate kinase function. This approach highlighted the essentiality of a specific kinase that is conserved between animals and choanoflagellates and provides tractable options for investigating protein functions in other emerging model systems with limited genetic tools.