Formation of recurring transient Ca2+-based intercellular communities during Drosophila hematopoiesis

Tissue development occurs through a complex interplay between many individual cells. Yet, the fundamental question of how collective tissue behavior emerges from heterogeneous and noisy information processing and transfer at the single-cell level remains unknown. Here, we reveal that tissue scale signaling regulation can arise from local gap-junction mediated cell-cell signaling through the spatiotemporal establishment of an intermediate-scale of transient multicellular communication communities over the course of tissue development. We demonstrated this intermediate scale of emergent signaling using Ca2+ signaling in the intact, ex vivo cultured, live developing Drosophila hematopoietic organ, the Lymph Gland (LG). Recurrent activation of these transient signaling communities defined self-organized signaling "hotspots" that receive and transmit information to facilitate repetitive interactions with non-hotspot neighbors, transfer information across cells, and regulate the developmental progression of hotspots. Overall, this work bridges the scales between single-cell and emergent group behavior providing key mechanistic insight into how cells establish tissue-scale communication networks. Significance statementCells coordinate their internal state and behavior by exchanging information with other cells in their vicinity. These local interactions are integrated across space and time to enable synchronized function at the tissue scale. Using live microscopy imaging of the Drosophila Lymph Gland, and by applying computational analyses, we identified and characterized a new mode of cellular communication through self-organized recurring coordinated short-term activation at the intermediate scale of 3-8 cells, which we call "hotspots". We reveal that hotspots form over the course of tissue development, and are dependent on specific proteins, called gap-junctions, that enable communication between adjacent cells. Hotspots repeatedly transmit and retrieve information to and from their non-hotspot neighbors to spread information throughout the tissue to regulate and coordinate tissue function.