BMP-dependent patterning of ectoderm tissue material properties modulates lateral mesendoderm cell migration during early zebrafish gastrulation

Cell migration is a fundamental process during embryonic development. Most studies in vivo have focussed on the migration of cells using the extracellular matrix (ECM) as their substrate for migration. In contrast, much less is known about how cells migrate on other cells, as found in early embryos when the ECM has not yet formed. Here, we show that lateral mesendoderm (LME) cells in the early zebrafish gastrula use the ectoderm as their substrate for migration. We show that the lateral ectoderm is permissive for the animal pole-directed migration of LME cells, while the ectoderm at the animal pole halts it. These differences in the permissiveness depend on the lateral ectoderm being more cohesive than the animal ectoderm, a property controlled by BMP signalling within the ectoderm. Collectively, these findings identify ectoderm tissue cohesion as one critical factor regulating LME migration during zebrafish gastrulation. Overall design: To investigate the differences in gene expression between animal and lateral ectoderm causing the difference in material properties between the two ectodermal tissues.