Control of tyrosinase gene expression and its relationship to neural crest induction in Rana pipiens. II. Measurement of tyrosinase mRNA accumulation during early embryogenesis using a specific cDNA probe.

The relationship between the process of neural induction and the control of tyrosinase gene expression in the cells that derive from the neural crest of amphibians has been examined at the molecular level. [3H] Tyrosinase cDNA was utilized as a probe to measure the levels of tyrosinase RNA transcripts present in Rana pipiens embryos from the time of fertilization through Stage 25 of cleavage (operculum complete, 240 h) and to correlate these levels with those published for the rate of tyrosinase protein synthesis. R. pipiens [3H]tyrosinase cDNA was synthesized from a purified tyrosinase mRNA template using avian myeloblastosis virus reverse transcriptase and was enriched for full length copies by preparative polyacrylamide gel electrophoresis. This cDNA product was estimated to represent greater than 90% by length of tyrosinase mRNA and hybridized to tyrosinase mRNA to greater than 97% within two orders of magnitude of R0t values. The extent of hybridization of [3H]tyrosinase cDNA to total embryonic RNA throughout early development paralleled the rate of synthesis of tyrosinase protein. Tyrosinase RNA transcripts were first detected at Stage 12-13 (0.0032% of total RNA) and rose to maximal levels by Stage 19 (0.011%). This represents a 50-fold increase from preinduction levels. These results are consistent with a model which predicts that one of the early events in the development of neural crest derivatives is the transcriptionally dependent accumulation of functionally mature tyrosinase mRNA.