Alternative splicing of a neural-specific Src mRNA (Src+) is a rapid and protein synthesis-independent response to neural induction in Xenopus laevis

Alternative splicing is used by the src protooncogene to derive two gene products, pp60c-src and pp60+. pp60+ is expressed exclusively in neurons, whereas pp60c-src is expressed in many tissues. The specific role of the src+ gene product in neurons is not yet understood. Expression of src+ mRNA begins early in neural development and is restricted to the neural plate in Xenopus embryos. Using a reverse transcription/polymerase chain reaction assay, we demonstrate that expression of src+ mRNA is dependent on neural induction. Src+ mRNA is expressed in animal cap ectoderm which is cocultured with mesoderm tissue, but not in ectoderm cultured alone. The protein kinase C (PKC) activator 12-O-tetradecanoylphorbol-13-acetate (TPA) induces src+ mRNA expression in cultured stage 10+ animal cap ectoderm. This induction is rapid, with src+ mRNA being detected within 1 hr of TPA addition. Only dorsal ectoderm tissue is competent to express src+ mRNA upon TPA treatment, and stage 10+ ectoderm tissue becomes unresponsive to TPA after 4 hr in culture. TPA-dependent induction of src+ mRNA in ectoderm tissue is not blocked by cycloheximide and therefore is not dependent on protein synthesis.