Ras-dependent maturation of Xenopus oocytes is blocked by modified peptides of GTPase activating protein (GAP)

RasGAP is involved in signal transduction triggered by FGF1 inXenopusoocytes expressing FGFR1

The role of RasGAP was investigated in the model system of Xenopus oocytes expressing fibroblast growth factor receptor 1 (FGFR1) stimulated by fibroblast growth factor 1 (FGF1). The injection of the SH2-SH3-SH2 domains of RasGAP suppressed Ras activity, extracellular signal-regulated protein kinase 2 (ERK2) phosphorylation and Mos synthesis. The SH2 domain of Src, and PP2, an inhibitor of Src, also abolished Ras activity, ERK2 phosphorylation and Mos synthesis. In addition, Src activity was blocked by the SH2-SH3-SH2 domains of RasGAP. Immunoprecipitation of a chimera composed of the extracellular domain of the platelet-derived growth factor (PDGF) receptor and the intracellular domain of FGFR1 stimulated by PDGF-BB demonstrates the recruitment of phosphorylated RasGAP. This study shows that the transduction cascade induced by the FGFR1-FGF1 interaction in Xenopus oocytes involves RasGAP as a co-activator of Src to stimulate the Ras/mitogen-activated protein kinase cascade and Mos synthesis. It emphasises a new positive regulatory role for RasGAP in FGFR transduction.

Modeling transcriptional regulation using microinjection into Xenopus oocytes

Transcriptional regulation is a complex process that requires cooperation between specific DNA sequence elements, the DNA-binding proteins that bind to these sequences, the general transcriptional machinery, and chromatin. Oocyte microinjection offers a technique to study the integrated transcription process while still providing the opportunity to experimentally perturb this process. We describe here techniques for manipulating DNA templates and the protein complement of the oocyte to study multiple facets of transcriptional regulation. We present sample results showing that the GAL4-VP16 fusion activator is sensitive to distance in constructs containing only a minimal promoter, but can activate transcription at greater distances when proximal promoter elements are present.