Targeting the cell membrane in established and emerging model organisms.

Transgenic markers and tools have revolutionised how we study cells and developing organisms. Some elements needed to construct those tools are universally applicable (e.g. fluorescent proteins), while others are species specific (e.g. cis-regulatory elements driving transcription). Membrane-localising signals that target proteins to the plasma membrane have been identified in some organisms, but their efficacy varies across species. To address this problem, we generated a toolkit of 11 membrane-localising tags that can be screened rapidly in diverse organisms. The toolkit includes tags targeting the plasma membrane through different mechanisms, including signal peptides, lipid attachments or fusion with lipid-binding domains. Each tag was fused to the fluorescent protein mScarlet3 and placed downstream of a T7 promoter, to produce mRNA that can be delivered in a wide range of embryos and cells. Through a collaborative effort, we tested this toolkit in ten animals spanning diverse phyla, including chordates, echinoderms, arthropods, nematodes, annelids, flatworms and cnidarians. We identify robust membrane-localising tags in each of these animals, and in the animals' closest relatives, the choanoflagellates. Three tags (KRas, GAP43 and Src64B) work in all the species we tested.