Monounsaturated fatty acids (MUFAs) play many important roles. They are incorporated into lipids such as membrane phospholipids where they influence membrane fluidity and triacylglycerols where they influence lipoprotein metabolism and adiposity. MUFAs are also the precursors to polyunsaturated fatty acids, which are important in processes such as cell signaling and membrane function. MUFAs are a significant fraction of the fatty acids in C. elegans. Synthesis of MUFAs is dependent on the activity of a family of three 9 desaturases, encoded for by
fat-5,
fat-6 and
fat-7. These desaturases introduce a double bond between the 9th and 10th carbons in 16- and 18-carbon fatty acids, the preferred substrates. The 9 desaturase, as the rate-limiting step for creation of MUFAs, is, therefore, highly regulated. We are studying the three C. elegans 9 desaturase knockouts obtained from Shohei Mitani (Tokyo Womens Medical University School of Medicine, Japan). We find that worms with mutations in
fat-5 or
fat-6 and
fat-5;
fat-6 are indistinguishable from wild-type worms in growth, movement, reproduction, and appearance. Analysis of their fatty acid profile shows a slight increase in saturated fatty acids and a decrease in MUFAs. The minor effect of these gene knockouts suggests
fat-7 can effectively satisfy the functions of
fat-5 and
fat-6. Indeed semi-quantitative RT-PCR reveals increased levels of
fat-7 mRNA in
fat-5,
fat-6, and
fat-5;
fat-6 mutants. In contrast, the
fat-7 knockout is embryonic lethal and must be maintained as a heterozygote. Using RNAi to deplete
fat-7 in developing larvae we find that worms become thin, slow growing, and unable to produce viable progeny. We have used these
fat-7 (RNAi) worms to examine the rescuing ability of various mono and poly unsaturated fatty acids. We have found that 18:19 and 18:2 fatty acids, but not 18:3 or 20:5, rescue
fat-7 (RNAi). Now we are testing 18:19 for its ability to rescue the
fat-7 homozygote. This work is just the beginning for understanding 9 fatty acid desaturation in the worm.