During preimplantation development, mouse embryos form a fluid-filled lumen. Pressurized fluid fractures cell–cell contacts and accumulates into pockets, which coarsen into a single lumen. How the embryo controls intercellular fluid movement during coarsening is unknown. Here we report inverse blebs growing into cells at adhesive contacts. Throughout the embryo we observed hundreds of inverse blebs, each filling with intercellular fluid and retracting within a minute. Inverse blebs grow due to pressure build-up resulting from fluid accumulation and cell–cell adhesion, which locally confines fluid. Inverse blebs retract due to actomyosin contraction, practically pushing fluid within the intercellular space. Importantly, inverse blebs occur infrequently at contacts formed by multiple cells, which effectively serve as fluid sinks. Manipulation of the embryo topology reveals that without sinks inverse blebs pump fluid into one another in futile cycles. We propose that inverse blebs operate as hydraulic pumps to promote luminal coarsening, thereby constituting an instrument used by cells to control fluid movement.

在植入前发育过程中，小鼠胚胎形成充满液体的管腔。加压液使细胞间接触破裂并积聚成袋，这些袋变粗成单个管腔。胚胎在粗化过程中如何控制细胞间液的运动尚不清楚。在这里，我们报告了在胶粘剂接触处生长到细胞中的反向气泡。在整个胚胎中，我们观察到数百个反向气泡，每个气泡都充满细胞间液并在一分钟内缩回。由于液体积聚和细胞间粘附导致压力积聚，局部限制液体，从而产生反向气泡。由于肌动球蛋白收缩，反向气泡回缩，实际上将液体推入细胞间隙内。重要的是，由多个细胞形成的接触处很少出现反向气泡，这些细胞有效地充当了液体汇。对胚胎拓扑结构的操纵表明，在没有汇的情况下，逆气泡会以徒劳的循环将流体相互泵入。我们提出反向气泡作为液压泵工作以促进管腔粗化，从而构成细胞用来控制流体运动的仪器。