HOMOLOGS OF THE XENOPUS DEVELOPMENTAL GENE DG42 ARE PRESENT IN ZEBRAFISH AND MOUSE AND ARE INVOLVED IN THE SYNTHESIS OF NOD-LIKE CHITIN OLIGOSACCHARIDES DURING EARLY EMBRYOGENESIS

The Xenopus developmental gene DG42 is expressed during early embryoni c development, between the midblastula and neurulation stages. The ded uced protein sequence of Xenopus DG42 shows similarity to Rhizobium No d C, Streptococcus Has A, and fungal chitin synthases. Previously, we found that the DG42 protein made in an in vitro transcription/translat ion system catalyzed synthesis of an array of chitin oligosaccharides. Here we show that cell extracts from early Xenopus and zebrafish embr yos also synthesize chitooligosaccharides. cDNA fragments homologous t o DG42 from zebrafish and mouse were also cloned and sequenced. Expres sion of these homologs was similar to that described for Xenopus based on Northern and Western blot analysis. The Xenopus anti-DG42 antibody recognized a 63-kDa protein in extracts from zebrafish embryos that f ollow ed a similar developmental expression pattern to that previously described for Xenopus. The chitin oligosaccharide synthase activity f ound in extracts was inactivated by a specific DG42 antibody; synthesi s of hyaluronic acid (HA) was not affected under the conditions tested . Other experiments demonstrate that expression of DG42 under plasmid control in mouse 3T3 cells gives rise to chitooligosaccharide synthase activity without an increase in HA synthase level. A possible relatio nship between our results and those of other investigators, which show stimulation of HA synthesis by DG42 in mammalian cell culture systems , is provided by structural analyses to be published elsewhere that su ggest that chitin oligosaccharides are present at the reducing ends of HA chains. Since in at least one vertebrate system hyaluronic acid fo rmation can be inhibited by a pure chitinase, it seems possible that c hitin oligosaccharides serve as primers for hyaluronic acid synthesis.