Increased gene dosage augments antifreeze protein levels in transgenic Drosophila melanogaster

One of the principal environmental adaptations of certain fishes inhabiting polar and northern coastal waters is the synthesis of antifreeze proteins (AFPs). AFPs bind to and prevent the growth of nascent ice crystals, thus d epressing the serum freezing point. The transgenic expression of AFP holds great promise for conferring freeze resistance to commercially important pl ant and animal species. Since fish at the greatest risk of freezing have mu ltiple AFP gene copies in order to synthesize higher levels of this protein , we have evaluated this evolutionary strategy as a way to maximize AFP exp ression in a model transgenic host, the fruit fly Drosophila melanogaster. A construct in which AFP genes of the Atlantic wolffish are fused to the Dr osophila yolk protein 1,2 promoter/enhancer region was transferred to flies through P-element mediated transformation. Several independent transgenic fly lines were used in genetic crosses to obtain multi-insert lines. Haemol ymph freezing point depression (thermal hysteresis) was greater in homozygo tes relative to heterozygotes for a given insert. Similarly, multi-insert l ines consistently displayed greater haemolymph AFP activity than the single insert lines from which they were derived. The thermal hysteresis value ob tained with a fly line harboring 8 AFP gene copies, 0.43 degrees C, represe nts the highest such value to date recorded in a transgenic host, and is ev en higher than the levels found in some AFP-producing fish.