Members of the mammalian β1,4-galactosyltransferase family are among the best studied glycosyltransferases, but the requirements for all members of this family within an animal have not previously been determined. Here, we describe analysis of two Drosophila genes, β4GalNAcTA (CG8536) and β4GalNAcTB (CG14517), that are homologous to mammalian β1,4- galactosyltransferases. Like their mammalian homologs, these glycosyltransferases use N-acetylglucosamine as an acceptor substrate. However, they transfer N-acetylgalactosamine rather than galactose. This activity, together with amino acid sequence similarity, places them among a group of recently identified invertebrate β1,4-N-acetylgalactosaminyltransferases. To investigate the biological functions of these genes, null mutations were generated by imprecise excision of a transposable element (β4GalNAcTA) or by gene-targeted homologous recombination (β4GalNAcTB). Flies mutant for β4GalNAcTA are viable and fertile but display behavioral phenotypes suggestive of essential roles for GalNAc-β1,4-GlcNAc containing glycoconjugates in neuronal and/or muscular function. β4GalNAcTB mutants are viable and display no evident morphological or behavioral phenotypes. Flies doubly mutant for both genes display only the behavioral phenotypes associated with mutation of β4GalNAcTA. Thus Drosophila homologs of the mammalian β4GalT family are essential for neuromuscular physiology or development but are not otherwise required for viability, fertility, or external morphology.
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