PROTEIN-TYROSINE KINASE-ACTIVITY FOLLOWING FERTILIZATION IS REQUIRED TO COMPLETE GASTRULATION, BUT NOT FOR INITIAL DIFFERENTIATION OF ENDODERM AND MESODERM IN THE SEA-URCHIN EMBRYO

The egg activation process functions to implement developmental progra ms that act much later in embryogenesis. One example of this is the fa ct that application of protein tyrosine kinase inhibitors to the ferti lized sea urchin egg for a 15-min period results in a defect in the ga strulation process occurring over 24 h later (Kinsey, W. H., Dev. Biol . 172, 704-707, 1995). In the present study, we show that the window o f sensitivity is not due to differential uptake of inhibitor, and esta blish that the inhibitor inhibits tyrosine kinase activity at the time of application. We also demonstrate that inhibition of protein tyrosi ne kinase activity in the zygote causes a specific defect in the morph ogenetic movements associated with gastrulation without interfering wi th the initial specification and differentiation of endoderm and mesod erm. Differentiation events occurring concurrent with or subsequent to gastrulation were also suppressed in embryos derived from treated zyg otes. These findings indicate that fertilization initiates a signaling cascade involving protein tyrosine kinase actitvity that is required specifically for events at gastrulation. This signaling event is requi red to complete the developmental program of both endoderm and mesoder m, but is different from those events necessary for initial specificat ion of endodermal and mesodermal cell fate. (C) 1998 Academic Press.