  During development, embryos perform a mesmerizing choreography, which is
crucial for the correct shaping, positioning and function of all organs. The
cellular properties powering animal morphogenesis have been the focus of much
attention. On the other hand, much less consideration has been given to the
invisible engine constituted by the intercellular fluid. Cells are immersed in
fluid, of which the composition and physical properties have a considerable
impact on development. In this review, we revisit recent studies from the
perspective of the fluid, focusing on basolateral fluid compartments and taking
the early mouse and zebrafish embryos as models. These examples illustrate how
the hydration levels of tissues are spatio-temporally controlled and influence
embryonic development.
