Stable and full rescue of the pigmentation in a medaka albino mutant by transfer of a 17 kb genomic clone containing the medaka tyrosinase gene

In the medaka Oryzias latipes, several albino strains have mutations in the tyrosinase gene that have been fully characterized at the molecular level. A genomic clone from wild-type medaka containing the 5 kb tyrosinase gene with its five exons, 10 kb of upstream sequences and 2 kb downstream sequen ces was introduced into fertilized eggs from a tyrosinase-negative albino s train. We show that the injection of this genomic clone predominantly confe rred mosaic expression ending before the hatching stage. A minority of juve niles retained a variable number of pigmented cells, including four individ uals keeping one pigmented eye through adulthood. Two of these could be mat ed, and one of these transmitted the transgene resulting in complete rescue of pigmentation to 16% of its offspring. The resulting transgenic line har bors a single copy of the wild-type tyrosinase gene and all fish are wild-t ype with respect to pigmentation. These experiments suggest that the tyrosi nase genomic clone, or a future shorter version of it, can be used in fish to routinely detect transgenic lines. The apparent faithful and systematic expression of the tyrosinase transgene is most probably due to the presence of a locus control region (LCR) in the injected clone. (C) 2000 Elsevier S cience B.V. All rights reserved.