Targeting the cell membrane in established and emerging model organisms.

Transgenic markers and tools have revolutionised how we study cells and developing organisms. Some of the 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 several model organisms. Unfortunately, the efficacy of these signals varies greatly 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 that target the plasma membrane through different mechanisms, including signal peptides, the attachment of lipids, and fusion with lipid-binding domains. Each tag has been fused to the red fluorescent protein mScarlet3 and placed downstream of a T7 promoter, allowing the in vitro production of mRNA that can be readily delivered in a wide range of embryos and cells of interest. Through a collaborative effort, we tested this toolkit in ten species of 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 one of animals' closest relatives, the choanoflagellates. Three tags (KRas, GAP43 and Src64B) work in all of the species tested.