The present invention features compositions (e.g., nucleic acids encoding fat-1, optionally and operably linked to a constitutively active or tissue-specific promoter or other regulatory sequence) and pharmaceutically acceptable formulations including nucleic acids encoding fat-1 or biologically active variants thereof and methods that can be used to effectively modify the content of PUFAs in animal cells (i.e., cells other than those of C. elegans, for example, mammalian cells such as myocytes, neurons (whether of the peripheral or central nervous system), adipocytes, endothelial cells, and cancer cells). The modified cells, whether in vivo or ex vivo (e.g., in tissue culture), transgenic animals containing them, and food products obtained from those animals (e.g., meat or other edible parts of the animals (e.g., liver, kidney, or sweetbreads)) are also within the scope of the present invention.