Abstract

Cell migration is a fundamental process in shaping organs and organisms. However, most of our knowledge in multicellular organisms regards extracellular matrix (ECM)-driven migration, whereas much less is known about how ECM -independent migration is regulated in vivo. To address this, we studied lateral mesendoderm (LME) migration in the early zebrafish gastrula, as it occurs without ECM . Our data show that LME cells use the ectoderm rather than the yolk cell membrane as the primary substrate while undergoing animally-directed movement. Additionally, we found that ectoderm is a pattern substate as lateral but not animal ectoderm is permissive to LME animal migration. Moreover, the permissiveness of the ectoderm is controlled by its tissue properties, as the lateral ectoderm is more rigid than the animal ectoderm. Indeed, tuning ectodermal contractility via the actin cytoskeleton is sufficient to reverse the migration patterns in response to lateral and animal ectoderm. Finally, BMP signalling is critical for delineating the nonpermissive animal ectoderm and inhibiting migration towards the animal pole. Our work points to the role of ectoderm patterning in directly modulating LME animally-directed migration. Furthermore, it suggests that the modulatory activity of the ectoderm is established by BMP signalling and relies on the material properties of the ectoderm tissue.