H. Inagaki et al., EXPRESSION OF THE TYROSINASE-ENCODING GENE IN A COLORLESS MELANOPHOREMUTANT OF THE MEDAKA FISH, ORYZIAS-LATIPES, Gene, 150(2), 1994, pp. 319-324
In the medaka fish Oryzias latipes many mutants for body colors have b
een isolated. Among them, a colorless melanophore mutant b, carrying b
alleles homozygously, has pigmented black eyes but orange-colored ski
n with amelanotic melanophores, suggesting the presence of a tissue-sp
ecific mechanism of melanin formation. To cast light on the molecular
basis of the mechanism, we have cloned cDNAs for tyrosinase (Tyr), a k
ey enzyme in melanin biosynthesis, from the wild-type (wt) fish. DNA s
equence analysis revealed that all clones encode a protein of 540 amin
o acids, having five potential glycosylation sites and two copper-bind
ing sites that are characteristic features of Tyr. Genomic DNA blot an
alysis disclosed that the Tyr gene is present as a single copy in the
fish genome. Using a cDNA clone as a probe, RNA blot analysis was carr
ied out. In the wt, the 2.2-kb Tyr mRNA was expressed in eyes and skin
but not in liver, corresponding to tissue-specific melanin formation,
In the b mutant, contrary to expectation, the mRNA was detected not o
nly in eyes but also in amelanotic skin. Therefore, pigmentation of th
e skin controlled by b is not directly related to expression of the Ty
r gene.