Dynamics of hydraulic and contractile wave-mediated fluid transport during Drosophila oogenesis

From insects to mice, oocytes develop within cysts alongside nurse-like sister germ cells. Prior to fertilization, the nurse cells’ cytoplasm is transported into the oocyte, which grows as its sister cells regress and die. Although critical for fertility, the biology and physics underlying this process are poorly understood. Here, we combined live imaging of germline cysts, genetic perturbations, and mathematical modeling to investigate the dynamics and mechanisms that enable cytoplasmic transport in Drosophila melanogaster egg chambers. We discovered that during “nurse cell (NC) dumping” most cytoplasm is transported into the oocyte independently of changes in myosin-II contractility, with dynamics instead explained by an effective Young–Laplace law, suggesting hydraulic transport induced by cell surface tension. A minimal flow-network model correctly predicts the directionality, intercellular pattern, and time scale of transport. Long thought to trigger transport through “squeezing,” changes in actomyosin contractility only play a role in the later stages of dumping. Our work thus demonstrates how biological and physical mechanisms cooperate during a critical developmental process that, until now, was thought to be mainly biochemically regulated.