A specific function of ER glucosylation enzymes in gastrulation of Drosophila embryos

The last steps in formation of the dolichol-glycan before transfer to nascent proteins in the ER are three consecutive glucosylations. These three glucosyl residues are assumed to function as a signal in ER quality control since they are recognised by the calreticulin/calnexin system and are clipped off before ER exit. Although these glucosylation enzymes have been studied in yeast, their function in development of multicellular organisms has remained unclear. We and others have identified mutations in these enzymes in Drosophila (Alg5/ wol, Alg6, Alg8/X-330). Surprisingly, mutant embryos show specific defects in gastrulation movements and germlayer formation. We have focused on the function in cell intercalation and found that the expression of the integral membrane protein E-Cadherin is strongly reduced. Unexpectedly E-Cadherin is partially glycosylated in mutant. The specific and non-redundant function of Alg6/8/5 is in contrast to enyzmes upstream in glycan synthesis and downstream in quality control. We found that mutations in Alg12 do not affect early
development suggesting a redundant function. In contrast mutations in Calnexin prevent oogenesis indidating a more general function than the glucosylation enzymes.We will present our detailed analysis of the mutant phenotype and molecular characterisation of Cadherin in wild-type and mutant embryos.