Stage-specific embryonic antigen-1 (SSEA-1), an antigenic epitope of which was defined as a Lewis x [Lex: Galβ1–4(Fucα1–3)GlcNAc-] carbohydrate structure, is widely expressed on the surface of mammalian cells, and is considered to be involved in cell-cell interactions during embryogenesis, differentiation, and neurodevelopmental processes. FUT3, FUT4, FUT5, FUT6 and FUT9 can synthesize the Lex structure, while FUT7 cannot (Kudo et al. 1998). Detailed analysis of the substrate specificity of polylactosamine acceptor has revealed FUT9 to have more-efficient activity for synthesis of the Lex structure than other α1,3FUTs (Nishihara et al. 1999).