During early embryonic development, many inductive interactions between tissues depend on signal transduction processes. We began to test the possibility that G-proteins participate in the signal transduction pathways that mediate neural induction. The expression during Xenopus development of three G alpha subunits, G alpha 0, G alpha i-1 and G alpha s-1, was characterized. The three maternally expressed genes showed different expression patterns during early development. Whole-mount in situ hybridization revealed that all three genes were expressed almost exclusively in the gastrula ectoderm and predominantly in the neuroectoderm in the neurula embryo. In order to investigate the involvement of these proteins in neural induction, we overexpressed the G-protein alpha subunits by injecting the G alpha mRNAs into fertilized eggs. Overexpression of G alpha s-1 increased the ability of gastrula ectoderm to become induced to neural tissue approximately four-fold. Overexpression of G alpha 0 and G alpha i-1 had less pronounced effects on neural competence, and inhibition of the G alpha 0 and G alpha i-1 proteins by pertussis toxin did not change the neural competence of the exposed gastrula ectoderm. Overexpression of the G alpha 0 and G alpha i-1 genes did, however, inhibit the normal disappearance of the blastocoel during gastrulation, suggesting a role for these G-proteins in regulating this process. The data also suggest a specific role for the G alpha s subunit in mediating the initial phases of neural induction.

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