One-eyed pinhead regulates cell motility independent of Squint/Cyclops signaling

In vertebrates, EGF-CFC factors are essential for Nodal signaling. Here, we show that the zygotic function of one-eyed pinhead, the zebrafish EGF-CFC factor, is necessary for cell movement throughout the blastoderm of the early embryo. During the blastula and gastrula stages, mutant cells are more cohesive and migrate slower than wild-type cells. Chimeric analysis reveals that these early motility defects are cell-autonomous; later, one-eyed pinhead mutant cells have a cell-autonomous tendency to acquire ectodermal rather than mesendodermal fates. Moreover, wild-type cells transplanted into the axial region of mutant hosts tend to form isolated aggregates of notochord tissue adjacent to the mutant notochord. Upon misexpressing the Nodal-like ligand Activin in whole embryos, which rescues aspects of the mutant phenotype, cell behavior retains the one-eyed pinhead motility phenotype. However, in squint;cyclops double mutants, which lack Nodal function and possess a more severe phenotype than zygotic one-eyed pinhead mutants, cells of the dorsal margin exhibit a marked tendency to widely disperse rather than cohere together. Elsewhere in the double mutants, for cells of the blastoderm and for rare cells of the gastrula that involute into the hypoblast, motility appears wild-type. Notably, cells at the animal pole, which are not under direct regulation by the Nodal pathway, behave normal in squint;cyclops mutants but exhibit defective motility in one-eyed pinhead mutants. We conclude that, in addition to a role in Nodal signaling, One-eyed pinhead is required for aspects of cell movement, possibly by regulating cell adhesion.