Jak1 kinase is required for cell migrations and anterior specification in zebrafish embryos.

Establishment of the vertebrate body plan requires a variety of signaling molecules. In a search for tyrosine kinases expressed in early zebrafish embryos, a model system for the study of vertebrate development, we discovered Jak1 kinase to be maternally encoded and the mRNA evenly distributed among the cells of blastula-stage embryos. Injection of RNA-encoding dominant-negative Jak1 kinases reduces a specific cell migration, epiboly, and results in the reduction of goosecoid expression and of anterior structures. This work establishes that, in addition to its role in signal transduction of cytokines in adult tissues, Jak1 kinase has a role in early vertebrate development.