PUFFFIN: A novel, ultra-bright, customisable, singleplasmid system for labelling cell neighbourhoods

Cell communication orchestrates development, homeostasis, and disease. Understanding these processes depends on effective methods to study how cells influence their neighbours. Here, we present Positive Ultra-bright Fluorescent Fusion For Identifying Neighbours (PUFFFIN), a novel cell neighbour-labelling system based upon secretion and uptake of a positively supercharged fluorescent protein s36GFP. To achieve sensitive labelling, we amplified the fluorescent signal by fusing s36GFP to the ultra-bright protein mNeonGreen. Secretor cells transfer s36GFP-mNeonGreen to neighbours while retaining a nuclear mCherry, making it straightforward to unambiguously identify, isolate, and profile neighbours of secretor cells. Transfer of the s36GFP-mNeonGreen fusion occurs within minutes, enabling even relatively transient interactions to be captured or tracked over time with live-imaging or flow cytometry. To enhance flexibility of use, we incorporated HaloTag technology to facilitate colour-of-choice labelling. To further increase the range of applications, we engineered a customisable single-plasmid construct composed of interchangeable components with option to incorporate any additional transgene. This allows users to manipulate the properties of a cell, while at the same time applying a fluorescent label to the surrounding cells. PUFFFIN offers a simple, sensitive, customisable approach to profile non-cell-autonomous responses to natural or induced changes in cell identity or behaviour in mammalian cells ### Competing Interest Statement The authors have declared no competing interest.