Koga A, Hori H
Division of Biological Science, Graduate School of Science, Nagoya University, Japan.
Pigment Cell Res. 1997 Dec;10(6):377-81. doi: 10.1111/j.1600-0749.1997.tb00695.x.
The i locus of the medaka fish, Oryzias latipes, is responsible for tyrosinase expression, and several mutant alleles have been identified. The genotype i1/i1 exhibits a complete albino phenotype, having pale orange-red skin and red eyes. This mutant lacks in vivo tyrosinase activity. The genotype i4/i4, on the other hand, shows a quasi-albino phenotype with skin as bright as that of i1/i1 but with red-wine-colored eyes. At the light microscope level, reduced pigmentation is observed both in the skin and eyes of this mutant. The tyrosinase genes for the i1 and the i4 alleles were cloned and sequenced, and compared with that of the wild-type tyrosinase gene. The i1 allele was found to contain a 1.9-kb transposable element in the 1st exon, and the i4 allele was found to contain a 4.7-kb transposable element in the 5th exon. Both i1 and i4 are alleles that were found in a commercial breeding population. The insertion of a transposable element thus appears to constitute a natural cause of mutations that cause albinism in this organism.
青鳉鱼（Oryzias latipes）的i基因座负责酪氨酸酶的表达，并且已经鉴定出了几个突变等位基因。基因型i1/i1表现出完全白化的表型，皮肤呈浅橙红色，眼睛为红色。这种突变体缺乏体内酪氨酸酶活性。另一方面，基因型i4/i4表现出准白化表型，其皮肤与i1/i1的一样亮，但眼睛呈红酒色。在光学显微镜水平上，在该突变体的皮肤和眼睛中均观察到色素沉着减少。克隆并测序了i1和i4等位基因的酪氨酸酶基因，并与野生型酪氨酸酶基因进行了比较。发现i1等位基因在第1外显子中含有一个1.9 kb的转座元件，而i4等位基因在第5外显子中含有一个4.7 kb的转座元件。i1和i4都是在商业繁殖群体中发现的等位基因。因此，转座元件的插入似乎构成了该生物体中导致白化病的突变的自然原因。
