Expression of the guanine nucleotide-binding protein Go correlates with the state of neural competence in the amphibian embryo

The nucleotide-binding protein Go is a transducing molecule closely associated with neural structures in vertebrates. Because of the potential importance of molecules of this type during the first step of neurogenesis, we have investigated the kinetics of expression of Go in the amphibian (Pleurodeles waltl) embryo, focusing our attention on the stages corresponding to the acquisition of neural competence by presumptive ectoderm and to the process of neural induction. Using affinity-purified IgGs directed against the alpha subunit of Go, Go-like immunoreaction (GoLI) is first detected at the midblastula stage in some animal cap (future ectodermal) cells just before they have attained competence to be neuralized. At the early gastrula stage, GoLI is almost exclusively expressed by neural-competent tissue as a whole, with no obvious difference between the dorsal (prospective neural) and the ventral (prospective epidermal) ectoderm. The expression of GoLI is therefore related to the state of competence of the tissue rather than to its fate. At the early neurula stage, immediately following neural induction, the expression of GoLI persists essentially in that part of ectoderm that has been diverted from epidermal differentiation towards the neural pathway; in the ventral ectoderm, as neural competence is lost GoLI disappears. Furthermore, in the neurectoderm, only approximately 70% of the cells conserve GoLI, demonstrating that immediately following neural induction the population of neurectodermal cells is not homogeneous.