Transfer of the gene for L-gulono-gamma-lactone oxidase, the missing enzyme in L-ascorbic acid biosynthesis in scurvy-prone animals, into medaka (Oryzias latipes) was successfully done. The expression plasmid pSVL-GLO. carrying rat liver L-gulono-gamma-lactone oxidase cDNA, was microinjected into the cytoplasm of fertilized eggs during the one-cell stage. Four male F-0 fish having the transgene in their germ cells came to maturity, and F-1 progeny derived from one of the F-0 fish possessed L-gulono-gamma-lactone oxidase activity, indicating that the transgene was functionally expressed in the fish. Genomic Southern blot analysis demonstrated that the transgene existed in both chromosome-integrated and extrachromosomal forms. (C) 1996 Academic Press, Inc.