Design principles of tissue organisation: How single cells coordinate across scales.

Cells act as building blocks of multicellular organisms, forming higher-order structures at different biological scales. Niches, tissues and, ultimately, entire organisms consist of single cells that remain in constant communication. Emergence of developmental patterns and tissue architecture thus relies on single cells acting as a collective, coordinating growth, migration, cell fate transitions and cell type sorting. For this, information has to be transmitted forward from cells to tissues and fed back to the individual cell to allow dynamic and robust coordination. Here, we define the design principles of tissue organisation integrating chemical, genetic and mechanical cues. We also review the state-of-the-art technologies used for dissecting collective cellular behaviours at single cell- and tissue-level resolution. We finally outline future challenges that lie in a comprehensive understanding of how single cells coordinate across biological scales to insure robust development, homoeostasis and regeneration of tissues.