Evidence for Antifreeze Protein Gene Transfer in Atlantic Salmon (Salmo salar)

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Abstract
Atlantic salmon (Salmo salar) freeze to death if they come into contact with ice at water temperatures below −0.7 °C. Consequently, sea-pen culture of this species in cold water is severely limited. Winter flounder (Pseudopleuronectes americanus) survive in ice-laden seawater by producing a set of antifreeze polypeptides (AFP). We are attempting to make the Atlantic salmon more freeze resistant by transferring antifreeze protein genes from the winter flounder to the genome of the salmon. Salmon eggs were microinjected with linearized DNA after fertilization. Individual fingerlings (1–2 g) were analyzed for flounder AFP genes by genomic Southern blotting. DNA from 2 out of 30 fingerlings showed hybridization to the flounder DNA probe. Hybridization bands following cleavage by restriction enzymes Sst l and Bam HI were identical to those of the injected DNA. Hybridization following Hind III digestion indicated that the flounder AFP gene was linked to the salmon genome. These hybridization signals were absent in the DNA from control fish. The intensity of the hybridization signals indicated that there was on average at least one copy of the AFP gene present per cell.