The Role of N-Linked Glycosylation During Drosophila Embryonic Development

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University of Delaware
N-linked glycosylation is a key post-translational modification for many secretory pathway targeted proteins. Endoplasmic reticulum glycosyltranferases construct a 14-sugar precursor on a dolichol carrier, which is transferred en mass to nascent peptides on asparagine consensus sites. Drosophila alg9 and alg10 Nglycosylation mutants were used to examine the role of this modification during development of the fly. The alg10 gene encodes the enzyme catalyzing terminal glucose addition to the sugar-precursor prior to transfer, while alg9 encodes an enzyme acting five steps earlier. In embryos, the loss of alg9 and alg10 causes severe and pleotrophic defects. Central nervous system (CNS) neurons were specified in both alg9 and alg10 embryos. Loss of alg10 disrupted axon pathfinding, while alg9 embryos lacked mature neurons. Drosophila eye development in the absence of alg9 and alg10 yielded small rough adult eyes, but the alg9 phenotype was more severe. Rescue of the alg10 rough eye phenotype by eye-specific expression of an alg10 transgene confirmed that the eye phenotype was caused by the loss of alg10. Examination of molecular markers in alg9 and alg10 late 3rd instar eye imaginal discs suggested adult small rough adult eyes might be due to neuronal apoptosis. These eye discs also showed defects in axon pathfinding, as shown by the loss of Bolwig’s nerve and disrupted axon tracks. All of these results are consistent with the hypothesis that loss of alg10 may disrupt the maturation of a subset of N-glycoproteins, while alg9 is essential for most or all N-glycoproteins, since it acts earlier and has far more severe developmental defects.