[Membrane lipids and galactose-recognizing lectin, galectin]

Although the main component of cell membrane is phospholipids, there are regions that are rich in glycosphingolipids and cholesterol, called membrane microdomains. Membrane microdomains are densely populated with receptors and intra/extracellular proteins that regulate signal transduction. Membrane microdomains move freely on cell membrane like floating rafts in the sea. In the presence of ligands, they associate with intracellular signaling molecules, regulating cellular functions. Most cell surface proteins including receptors and secreted proteins are glycosylated and interact with lectins that recognize specific glycan structures. Glycan-lectin binding plays an important role in regulating cellular function. Glycans on receptors and ligands and on glycosphingolipids abundant in membrane microdomains are recognized and crosslinked by endogenous lectins, regulating the behavior of cell surface molecules such as receptors. We have been investigating the in vivo function of galactose-recognizing galectins. Fifteen subtypes of galectins exist in mammals, and they are widely distributed throughout the body including the gastrointestinal tract, urogenital tract, and immune system in a tissue- and cell-specific manner. While analyzing the function of galectins in the mechanism controlling the function of the corpus luteum, which produces progesterone essential for the establishment and maintenance of pregnancy, we discovered that cell membrane lipids play a central role in regulating luteal function. Here, we introduce the involvement of cell membrane lipids, particularly a lipid-derived mediator, prostaglandin E, and the qualitative and quantitative changes in glycosphingolipids, as well as galactose-recognizing galectins in the mechanism controlling human corpus luteum function.