Development of an optimized synthetic Notch receptor as an in vivo cell-cell contact sensor [Developmental Biology]

Detection and manipulation of direct cell–cell contact in complex tissues is a fundamental and challenging problem in many biological studies. Here, we report an optimized Notch-based synthetic receptor (synNQ) useful to study direct cell–cell interactions in Drosophila. With the synNQ system, cells expressing a synthetic receptor, which contains Notch activation machinery and a downstream transcriptional activator, QF, are activated by a synthetic GFP ligand expressed by contacting neighbor cells. To avoid cis-inhibition, mutually exclusive expression of the synthetic ligand and receptor is achieved using the “flippase-out” system. Expression of the synthetic GFP ligand is controlled by the Gal4/UAS system for easy and broad applications. Using synNQ, we successfully visualized cell–cell interactions within and between most fly tissues, revealing previously undocumented cell–cell contacts. Importantly, in addition to detection of cells in contact with one another, synNQ allows for genetic manipulation in all cells in contact with a targeted cell population, which we demonstrate in the context of cell competition in developing wing disks. Altogether, the synNQ genetic system will enable a broad range of studies of cell contact in developmental biology.