Transgenic pigs expressing plant genes.

F atty acids are a group of lipids that consist of a carboxyl group plus a long hydrocarbon chain. Saturated fatty acids have single carbon–carbon bonds, whereas unsaturated fatty acids contain one or more double bonds within the hydrocarbon chain. Polyunsaturated fatty acids (PUFAs) have two main functions: the first is a critical role in membrane structure where they confer fluidity and flexibility, and the second is their role as precursors of prostaglandins, leukotrienes, and glycolipids, all of which are essential in the regulation of various biological functions. Mammals lack the enzyme to create double bonds between the ninth carbon (from the carboxyl end) and the terminal methyl group and thus cannot synthesize linoleic acid (18:2n-6) and -linolenic acid (18:3n-3), making these fatty acids an essential component of the mammalian diet (vitamin F). Plants, including spinach, produce these essential PUFAs by desaturating oleic acid (18:1n-9) at positions C-12 and C-15 to produce 18:2n-6 (linoleic acid) and 18:3n-3 (linolenic acid). Thus, the fatty acid desaturases constitute an important category of enzymes involved in the synthesis of PUFAs. The genes for the desaturases have been identified in various plant systems and in simple organisms including Caenorhabditis elegans (1). These enzymes have also been shown to be functional in mammalian cells on transfection (2). The article by Saeki et al. (3) in a recent issue of PNAS takes this research a significant step further by showing constitutive expression and activity of the 12 spinach desaturase gene (FAD2) in transgenic pigs. Levels of linoleic acid (18:2n-6) in adipocytes collected from transgenic pigs and cultured in vitro were 10-fold higher than in wild-type control cells. Biopsied white adipose tissue from transgenic pigs contained 20% more linoleic acid than that of the nontransgenic controls. This study is the first time that a plant gene has been functionally expressed in a complex mammalian system. This success may open the road toward the production of pork that is better for the consumer. Both cardioprotective effects and anticancer activity have been documented for the n-3 fatty acids, which are also important for normal function and development of the retina and the brain. For these reasons, a large market has developed for fish-oil capsules consumed by health-conscious individuals. Pigs have been fed a PUFA-rich diet, which has improved processing and increased PUFA concentrations in pork. The article by Saeki et al. is important for its interesting approach to the production of more healthful pork and diversification of the range of products available from domesticated animals. In the study by Saeki et al. (3) microinjection technology was used to create FAD2-transgenic pigs. This well established technology involves injection of several thousand copies of a particular gene into the pronuclei of zygotes, a developmental stage shortly after fertilization when the sperm tail has vanished and the sperm head is transformed into the male