APOE is an apolipoprotein, a protein associating with lipid particles, that mainly functions in lipoprotein-mediated lipid transport between organs via the plasma and interstitial fluids. APOE is a core component of plasma lipoproteins and is involved in their production, conversion and clearance. Apoliproteins are amphipathic molecules that interact both with lipids of the lipoprotein particle core and the aqueous environment of the plasma. Homotetramer. Highly expressed in the yolk syncytial layer during embryonic (starting at the blastula stage) and early larval development, an extraembryonic structure implicated in embryonic and larval nutrition. Also observed in the deep cell layer during blastula stage, in numerous ectodermal derivatives after gastrulation, and after 3 days of development in a limited number of cells both in brain and in the eyes. Belongs to the apolipoprotein A1/A4/E family.