Tyrosinase gene expression in zebrafish embryos.

The enzyme tyrosinase is required for the conversion of tyrosine into the pigment melanin. Thus, tyrosinase gene expression is a useful marker for studying the differentiation of melanin-expressing cells during embryogenesis. We describe the spatiotemporal pattern of transcription of the tyrosinase gene and the presence of active enzyme in whole embryos of the zebrafish, Danio rerio. At 16.5 h post-fertilisation the tyrosinase gene is transcribed in the dorsal extremity of the developing retinal pigment epithelium, approximately 7 h before visible pigmentation. Shortly thereafter, transcription in neural crest-derived melanocytes is first observed dorsolateral to the mesencephalon and diencephalon and the posterior hindbrain/anterior spinal cord. A wave of gene activation and cell migration is then observed moving towards the posterior of the animal. DOPA staining for tyrosinase activity shows the presence of active enzyme in embryos at least 3 h before visible pigmentation.