Membrane Microdomain as a Platform of Carbohydrate-Mediated Interactions During Early Development of Medaka Fish
Membrane microdomains, which are often called lipid rafts, are a platform of signal transduction in various biological processes like recognition and cell growth, because they contain not only receptors for ligands and growth factors, but also downstream signal transducer molecules on the same microdomains. Membrane microdomains are rich in cholesterol and glycosphingolipids and concentrate on particular proteins and carbohydrates in the restricted membrane area. Our group has recently demonstrated that membrane microdomains isolated from sperm function as a platform not only for signal transduction in sperm activation (Ohta et al. 1999, 2000), but also for sperm-egg binding at fertilization of sea urchin (Maehashi et al. 2003). In fertilization, sperm binding to the vitelline coat is the first step of the sperm-egg binding and at least two kinds of interactions occur. One is a protein-protein interaction between bindin and the sperm binding protein (SBP) localized in vitelline coat. The other is a carbohydrate-protein interaction between the glycolipids of sperm microdomain and the SBP (Maehashi et al. 2003). The most striking feature is that these two interactions concomitantly occur on the membrane microdomains. Furthermore, the sperm microdomains also contain transducer proteins like Src-family kinase and adenylate cyclase (Ohta et al. 2000). Therefore, co-localization of those proteins and carbohydrates involved in cell adhesion with those transducer proteins involved in signal transduction in the microdomains suggests the important roles of the membrane microdomain in carbohydrate- and protein-mediated interactions in the sperm-egg binding.
KeywordsTransducer Protein Membrane Microdomains Oryzias Latipes Medaka Embryo Blastodermal Cell
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