Figure 4.

LIPSTIC (Labeling Immune Partnerships by SorTagging Intercellular Contacts) utilizes the Staphylococcus aureus transpeptidase sortase A (SrtA) that can transfer peptides with LPXTG motifs to proteins containing five N-terminal glycine residues (G5) (Pasqual et al., 2018). By fusing SrtA to a ligand in a donor cell type and G5 to the cognate receptor of a receiver cell type, addition of LPETG marks the recipient G5-expressing cell. synNotch (synthetic Notch) is a versatile system in which a donor cell expresses a ligand or antigen, such as surface GFP, and the receiver cell expresses a chimeric receptor consisting of an extracellular sensing module such as an anti-GFP nanobody, a Notch core, and an intracellular transcription factor (Morsut et al., 2016). When the sensing module of the receiver cell is activated by interaction with the donor cell, the Notch core is cleaved leading to release of a transcription factor, such as Gal which can then activate downstream UAS reporters. G-baToN (GFP-based Touching Nexus) similarly utilizes surface GFP expression on a donor cell and anti-GFP nanobody expression on a receiver cell (Tang et al., 2020). Interaction of surface GFP with the anti-GFP nanobody leads to endocytosis and transfer of the GFP from the donor cell to the receiver cell, allowing for downstream analysis. mCherry-niche overexpresses a soluble and lipid permeable form of mCherry in donor cells, which is then acquired by neighboring receiver cells (Ombrato et al., 2019). By expressing mCherry-niche in GFP+ cancer cells, they can be distinguished from GFP - microenvironment cells that receive mCherry.