Phosphorylation of phospholipase C gamma 1 and its association with the FGF receptor is developmentally regulated and occurs during mesoderm induction in Xenopus laevis.

We have examined phosphorylation of phospholipase C gamma 1 (PLC gamma 1) and its association with FGFR1 during mesoderm induction in animal pole explants and during early development in Xenopus embryos. In explants, PLC gamma 1 became associated with FGFR1 during mesoderm induction by FGF or by vegetal cells, the source of the natural inducer. Both PLC gamma 1 and FGFR1 were phosphorylated on tyrosine, indicating that both proteins were activated. Phosphorylation of these two proteins occurred very early during the induction process (within 0.5 hr), providing evidence that a member of the FGF family is a component of the vegetal inducing signal. PLC gamma 1 was also associated with FGFR1 in Xenopus blastulae and this association was specific to presumptive mesoderm cells. Examination of the PLC gamma 1 phosphorylation pattern during early Xenopus development and its association with FGFR1 revealed that maximum phosphorylation and association of these two proteins occurred during early- to mid-blastula stages, concurrent with mesoderm induction in vivo. This spatiotemporal pattern PLC gamma 1-FGFR1 association and phosphorylation suggests that PLC gamma 1 is involved in intracellular signaling during mesoderm induction in Xenopus. Seven additional phosphotyrosyl bands were coimmunoprecipitated with either PLC gamma 1 or FGFR1 from Xenopus blastulae; these bands may represent additional components of an FGFR1 signaling complex. One of these phosphotyrosyl bands was identified as NCK. In addition, growth factor receptor-binding protein, and son-of-sevenless two upstream regulators of RAS signaling, were co-immunoprecipitated with FGFR1.