Hydraulic fracturing and active coarsening position the lumen of the mouse blastocyst

The making of a lumen During the early days of mammalian development, the formation and positioning of a fluid-filled lumen, the blastocoel, defines the first axis of embryo symmetry. Dumortier et al. describe how a blastocoel lumen arises from the hydraulic fracturing of cell-cell contacts into hundreds of micrometer-size water pockets that then form a single large lumen (see the Perspective by Arroyo and Trepat). The authors characterized the process of lumen formation mechanically and molecularly and were able to manipulate the first axis of symmetry of the mammalian embryo experimentally. Thus, fluid dynamics plays a key role in the embryo and may play a similar role in the formation of other biological cavities. Science , this issue p. 465 ; see also p. 442