Expression cloning and characterization of a novel murine α1,3- fucosyltransferase, mFuc-TIX, that synthesizes the Lewis x (CD15) epitope in brain and kidney

The 3-fucosyl-N-acetyllactosamine (Lewis x, CD15, SSEA-1) carbohydrate epitope is widely distributed in many tissues and is developmentally expressed in some rodent and human tissues, i.e. brain and lung, and mouse early embryo. In such tissues, the Lewis x epitope is considered to be involved in cell-cell interactions. We isolated a novel mouse α1,3- fucosyltransferase gene, named mFuc-TIX, from an adult mouse brain cDNA library using the expression cloning method. On flow cytometric analysis, Namalwa cells transfected stably with the mFuc-TIX gene showed a marked increase in Lewis x epitopes but not sialyl Lewis x epitopes. As seen experiments involving oligosaccharides as acceptor substrates, mFuc-TIX transfers a fucose to lacto-N-neotetraose but not to either α2,3-sialyl lacto-N-neotetraose or lacto-N~tetraose. The substrate specificity of mFucTIX was similar to that of mouse myeloid-type α1,3-fucosyltransferase (mFuc-TIV). The deduced amino acid sequence of mFuc-TIX, consisting of 359 residues, indicated a type II membrane protein and shows low degrees of homology to the previously cloned α1,3-fucosyltransferases, i.e. mFuc-TIV (48.4%), mouse Fuc-TVII (39.1%), and human Fuc-TIII (43.0%), at the amino acid sequence level. A phylogenetic tree of the α1,3-fucosyltransferases constructed by the neighbor-joining method showed that mFuc-TIX is quite distant from the other α1,3-fucosyltransferases. Thus, mFuc-TIX does not belong to any subfamilies of known α1,3Fuc-Ts. The mFuc-TIX transcript was mainly detected in brain and kidney with the Northern blotting and competitive reverse transcription-polymerase chain reaction methods, whereas the mFuc-TIV transcript was not detected in brain with these methods. On in situ hybridization, the mFuc-TIX transcript was detected in neuronal cells but not in the glial cells including astrocytes. These results strongly indicated that mFuc-TIX participates in the Lewis x synthesis in neurons of the brain and may be developmentally regulated.