We have shown that these fatty acids then undergo the expected metabolic processing and are incorporated into more complex lipid species that can then be subject to transport via lipoproteins. Herein, we describe an isotopic labeling technique using either fluorescent or radioactive fatty acids that are injected directly into the yolk of lecithotrophic embryos and larvae (24 hpf to 4 dfp). Because of this issue, it was imperative to design a method to study lipid metabolism at earlier developmental stages. However, these genes can be examined successfully using pharmacological approaches. These essential genes are poor candidates for genetic screens involving the uptake of exogenous food after 5 dpf because the animals are either too deformed or dead.

Genes involved in lipid and lipoprotein metabolism are frequently expressed early in embryonic development and are occasionally required for proper embryo development and/or viability. These methods are outlined in this chapter.

Further, we have pioneered the use of both fluorescently and radiolabeled lipids for biochemical studies of metabolism and transport at multiple stages of Zebrafish embryo and larval development. Several groups, including our own, have developed methods to image fatty acid metabolism using fluorescently labeled fatty acids coupled with a variety of fluorescence microscopy techniques. Zebrafish provide a unique model where in just 6 days, one can study lipid metabolism in live metabolic organs such as the liver and intestine. Zebrafish are emerging as an ideal model for examining not only the fundamentals of lipid biology, such as dietary lipid absorption and lipoprotein biology, but also aspects of lipid biology related to obesity, metabolic disorders, and cardiovascular disease. A better grasp of how altered lipid metabolism contributes to specific disease pathologies requires extensive studies of the fundamentals of lipid metabolism, storage, and transport in experimentally tractable whole-animal models. The misregulation of lipids observed in a variety of human dyslipidemias is a major factor in these very prevalent chronic diseases. Chronic diseases (affecting more than ½ of adults in the US) cause poor health, disability, and death, and represent the bulk of the US health-care expenditures. In metazoans, lipids play additional essential roles in metabolic functions and physiology. In all cells, lipids are essential molecules that support cellular membrane structure, promote inter- and intracellular signaling, and serve as fundamental sources of fuel.

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