The Alg5 ortholog Wollknäuel is essential for correct epidermal differentiation during Drosophila late embryogenesis

The formation of an extracellular matrix (ECM) presup-poses an ordered delivery of its components to ensure its stereotypic architecture. The Drosophila cuticle is an ECM produced by the epidermis at its apical site and is charac-terized by a layered organization. To understand the mechanisms of cuticle assembly during development, we have investigated early aspects of protein N-glycosylation, i.e. the attachment of a dolichol-linked oligosaccharide to distinct Asn sites of a protein known to be essential for sorting in the secretory pathway. Mutations in the Drosophila alg5 gene wollknäuel (wol) that codes for an enzyme initiating the glucosylation of the dolichol-linked oligosaccharide decrease, as expected, glucosylation and the amounts of N-glycosylated proteins such as the cuticle-organizing factor Knickkopf, without affecting their correct localization. At the same time, the polarity deter-minants Crumbs and atypical protein kinase C accumu-late at the apical plasma membrane in wol deficient embryos. In part, these perturbations may also be caused by the unfolded protein response, which is commonly trig-gered by ER stress and downsizes transcription and trans-lation in general. In any case, they are associated with the loss of cuticle layering and aberrant apical plasma mem-brane organization suggesting that glucosylation, either directly or indirectly through controlling protein degra-dation, is important for the efficient and balanced deploy-ment of the biochemical functions of secreted and membrane-associated proteins during epidermal differentiation