Collective Growth in a Small Cell Network

Theoretical studies suggest that many of the emergent properties associated with multicellular systems arise already in small networks [1, 2]. However, the number of experimental models that can be used to explore collective dynamics in well-defined cell networks is still very limited. Here we focus on collective cell behavior in the female germline cyst in Drosophila melanogaster, a stereotypically wired network of 16 cells that grows by ∼4 orders of magnitude with unequal distribution of volume among its constituents. We quantify multicellular growth with single-cell resolution and show that proximity to the oocyte, as defined on the network, is the principal factor that determines cell size; consequently, cells grow in groups. To rationalize this emergent pattern of cell sizes, we propose a tractable mathematical model that depends on intercellular transport on a cell lineage tree. In addition to correctly predicting the divergent pattern of cell sizes, this model reveals allometric growth of cells within the network, an emergent property of this system and a feature commonly associated with differential growth on an organismal scale [3].