FUT4 and FUT9 genes are expressed early in human embryogenesis

The Le(X) oligosaccharide is expressed in organ buds progressing in mesench yma, during human embryogenesis. Myeloid-like alpha 3-fucosyltransferases a re good candidates to synthesize this oligosaccharide, We investigated by N orthern analysis all the alpha 3-fucosyltransferase gene transcripts and on ly FUT4 and FUT9 were detected. The enzymes encoded by the FUT4 and FUT9 ge nes are the first alpha 3-fucosyltransferases strongly expressed during the first two months of embryogenesis. The Northern profile of expression of t he embryo FUT4 transcripts is similar in size and sequence to the known FUT 4 transcripts of 6 kb, 3 kb, and 2.3 kb, but a new FUT9 transcript of 2501 bp, different from the known mouse (2170 bp) and human (3019 hp) transcript s was cloned. FUT3, FUT5, FUT6, and FUT7 were not detected by Northern blot . The FUT3 and FUT6 transcripts start to appear at this stage, but are only detected by reverse transcriptase-PCR analysis. The expression of FUT5 is weaker than FUT3 and FUT6 and the RT-PCR signal is faint and irregular. FUT 7 is not detected at all. Using mRNA from 40-to 65-day-old embryos, we have prepared different hexamer and oligo-dT cDNA libraries and cloned, by rapi d amplification cDNA ends-PCR, FUT4 and FUT9 a3-fucosyltransferase transcri pts. The tissue expression of the embryonic FUT9 transcript is closer to th at observed for the mouse (brain), than to the known human (stomach) transc ripts. The acceptor specificity and the kinetics of the a3-fucosyltransfera se encoded by this FUT9 transcript are similar to the FUT4 enzyme, except f or the utilization of the lac-di-NAc acceptor which is not efficiently tran sformed by the FUT9 enzyme. Like FUT4, this embryonic FUT9 is N-ethylmaleim ide and heat resistant and the corresponding gene was confirmed to be local ized in the chromosome band 6q16, Finally, this FUT9 transcript has a singl e expressed exon as has been observed for most of the other vertebrate alph a 2- and a3-fucosyltransferases.