An early developmental phase of pp60c-src expression in the neural ectoderm.

The expression of the normal cellular src protein (pp60c-src) was investigated in the early chick embryo during gastrulation and neurulation by immunoperoxidase staining using antisera, raised against bacterially expressed pp60v-src, that recognizes pp60c-src specifically in normal cells. During gastrulation pp60c-src immunoreactivity appeared primarily in the neural ectoderm and was much less prominent in the mesoderm, endoderm, and nonneural ectoderm. During neurulation pp60c-src immunoreactivity began to disappear from the wall of the closing neural tube so that by the completion of neural tube closure no specific pp60c-src immunoreactivity appeared in any of the neuroepithelial cells composing the neural tube. These studies reveal a developmental phase of pp60c-src expression even earlier than reported previously, when neuroepithelial cells of later embryos undergo terminal neuronal differentiation. These findings raise the possibility that pp60c-src may mediate two different differentiation signals in the neuronal lineage.