earticle

영어

It has been shown that membrane microdomains (or rafts) are important as a hot spot for signal transduction. However, little attention has been paid to the fact that glycan chains are enriched in the microdomains. We have recently proposed a hypothesis that the microdomains are involved in the protein- and glycan-mediated cell adhesion and the subsequent signal transduction, and have demonstrated it in sperm-egg interactions at fertilization of sea urchin [1-3] To extend this hypothesis in early embryogenesis, we have studied on microdomains in developing embryos of medaka fish, Oryziaslatipes. Here wes how several lines of evidence supporting our hypothesis: (i) The micro domains prepared from early gastrula embryos were rich in cholesterol and sphingomyelin, and contained E-cadherin and LeX-glycan-containing glycoproteins (LeX-gp) and glycolipids (LeX-gsl), together with transducer proteins like c-Srckinase. The LeX-glycans and E-cadherin are known to be involved in morula compaction (tight cell adhesion) in mouse; (ii) Disruption of the microdomains of early gastrula embryos by treatment with methyl-b-cyclodextrin (MBCD) or C2-ceramide, impaired epiboly, the first cell migration event that occurs during gastrulation process. The most typical phenotype of the microdomain-disrupted embryo was detachment of blastodermal cells. Interestingly, the MBCD-induced disruption of microdomains and the epiboly impairment were restored when cholesterol was added back to the embryos. Thus, microdomain formation is critical in epiboly [4]; (iii) The isolated microdomains could bind to the microdomains in the presence of Ca2+ in LeX-glycan- and E-cadherin-dependent manners. These results suggest that the microdomain formation is important in the protein- and carbohydrate-mediated cell-cell interactions.