From insects to mice, oocytes develop within cysts alongside nurse-like sister germ cells. Prior to fertilization, the nurse cells’ cytoplasmic contents are transported into the oocyte, which grows as its sister cells regress and die. Although critical for fertility, the biological and physical mechanisms underlying this transport 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 directional and complete 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 baseline cell-surface tension. A minimal flow-network model inspired by the famous two-balloon experiment and motivated by genetic analysis of a myosin mutant correctly predicts the directionality, intercellular pattern, and time scale of transport. Long thought to trigger transport through “squeezing,” changes in actomyosin contractility are required only once NC volume has become comparable to nuclear volume, in the form of surface contractile waves that drive NC dumping to completion. Our work thus demonstrates how biological and physical mechanisms cooperate to enable a critical developmental process that, until now, was thought to be mainly biochemically regulated.

从昆虫到小鼠，卵母细胞在囊肿内与护士般的姐妹生殖细胞一起发育。在受精之前，护士细胞的细胞质内容物被运送到卵母细胞中，随着其姐妹细胞的退化和死亡，卵母细胞会生长。尽管对生育至关重要，但人们对这一运输过程背后的生物学和物理机制知之甚少。在这里，我们结合胚系囊肿的实时成像、遗传扰动和数学建模来研究在黑腹果蝇中实现定向和完整细胞质转运的动力学和机制蛋室。我们发现，在“护理细胞 (NC) 倾倒”期间，大多数细胞质被转运到卵母细胞中，而不受肌球蛋白 II 收缩力的变化影响，而动力学则由有效的杨拉普拉斯定律解释，表明由基线细胞表面张力诱导的水力转运. 受著名的双气球实验启发并受肌球蛋白突变体遗传分析启发的最小流动网络模型正确预测了运输的方向性、细胞间模式和时间尺度。长期以来一直认为通过“挤压”触发运输，只有当 NC 体积变得与核体积相当时，肌动球蛋白收缩力的变化才需要，以表面收缩波的形式驱动 NC 倾倒完成。