Structure and developmental expression of the ascidian TRP gene: insights into the evolution of pigment cell-specific gene expression.
The tyrosinase family in vertebrates consists of three related melanogenic enzymes: tyrosinase, tyrosinase-related protein-1 (TRP-1), and TRP-2. These proteins control melanin production in pigment cells and play a crucial role in determining vertebrate coloration. We have isolated a gene from the ascidian Halocynthia roretzi which encodes a tyrosinase-related protein (HrTRP) with 45-49% identity with vertebrate TRP-1 and TRP-2. The expression of the HrTRP gene in pigment lineage a8.25 cells starts at the early-mid gastrula stage, which coincides with the stage when these cells are determined as pigment precursor cells; therefore, it provides the earliest pigment lineage-specific marker, which enables us to trace the complete cell lineage leading to two pigment cells in the larval brain. In addition, the expression pattern of the HrTRP gene appears to share similar characteristics with the mouse TRP-2 gene although structurally the HrTRP gene is more closely related to mammalian TRP-1 genes. Based on these observations and on results from molecular phylogenetic and hybridization analyses, we suggest that triplication of the tyrosinase family occurred during the early radiation of chordates. Initially, duplication of an ancestral tyrosinase gene produced a single TRP gene before the urochordate and cephalochordate-vertebrate divergence, and a subsequent duplication of the ancestral TRP gene in the vertebrate lineage gave rise to two TRP genes before the emergence of teleost fishes. Evolution of the melanin synthetic pathway and possible phylogenetic relationships among chordate pigment cells that accommodate the metabolic process are discussed. Dev Dyn 1999;215:225-237.
Sato
S
S
Biological Institute, Graduate School of Science, Tohoku University, Miyagi, Japan.
Toyoda
R
R
Katsuyama
Y
Y
Saiga
H
H
Numakunai
T
T
Ikeo
K
K
Gojobori
T
T
Yajima
I
I
Yamamoto
H
H
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D019070:Cell Lineage; D002816:Chordata, Nonvertebrate / Q000196:embryology / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D004790:Enzyme Induction; D019143:Evolution, Molecular; D005091:Exons / Q000235:genetics; D005136:Eye Proteins / Q000096:biosynthesis / Q000235:genetics; D005775:Gastrula / Q000201:enzymology; D020440:Gene Duplication; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D005796:Genes; D005801:Genes, Homeobox; D006054:Goldfish; D019746:Intramolecular Oxidoreductases / Q000235:genetics; D007438:Introns / Q000235:genetics; D007814:Larva; D008322:Mammals / Q000235:genetics; D008543:Melanins / Q000096:biosynthesis; D008562:Membrane Glycoproteins; D051379:Mice; D008969:Molecular Sequence Data; D008970:Molecular Weight; D014442:Monophenol Monooxygenase / Q000235:genetics; D005810:Multigene Family; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000235:genetics; D010088:Oxidoreductases; D010802:Phylogeny; D010858:Pigmentation / Q000235:genetics*; D014176:Protein Biosynthesis; D011506:Proteins / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D014561:Urochordata / Q000196:embryology / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development
D018076:DNA, Complementary; D005136:Eye Proteins; D008543:Melanins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D011506:Proteins; D010088:Oxidoreductases; C079621:Tyrp1 protein, mouse; C064056:tyrosinase-related protein-1; D014442:Monophenol Monooxygenase; D019746:Intramolecular Oxidoreductases; C042501:dopachrome isomerase