The Role Of N-Linked Glycosylation In Drosophila Development
Date
2016-05
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
Asparagine-linked or N-linked glycosylation is an important post-translational
modification pathway that adds a 14-sugar oligosaccharide to target proteins on the
luminal side of the endoplasmic reticulum. These glycan “tags” are necessary for
multiple cellular functions including cell-cell recognition, protein trafficking, and
proper protein folding. The focus of this study is to examine the effect of loss of
function mutations in the N-linked pathway. A group of human diseases, congenital
disorders of glycosylation (CDG), arise from mutations in the genes involved in
various steps of this pathway. While CDGs display pleotropic phenotypes, most
include neuronal defects. The two specific genes under study in this project are alg9
and alg10. Each encode a glycosyltransferase that adds a sugar residue to the growing
oligosaccharide chain. The Drosophila eye is used as a model organ to study the
effects of these genes on neuronal development. In adult flies, these mutations yield a
small rough eye phenotype, which is more severe in alg9, as it acts five steps before
alg10 in the pathway. In order to determine the basis of this phenotype, larval eye
discs were dissected, stained for different glycoprotein and neuronal markers, and then
imaged using confocal microscopy. We found these mutations interrupt proper
glycoprotein trafficking, as the axonal surface glycoprotein Chaoptin accumulates in
the cell bodies of alg9 and alg10 mutant photoreceptors. Caspase-3 staining showed
this accumulation eventually leads to photoreceptor apoptosis. Photoreceptor death
likely continues through pupal development resulting in a reduced number of
photoreceptors in alg10 adult eyes and almost complete absence in alg9 adult eyes. These results indicate that CDG patients may have normal neuronal specification and
differentiation, but experience neuronal deficits due to intracellular accumulation of
glycoproteins leading to cell death. These data suggest markers of endoplasmic
reticulum stress and the unfolded protein response should be examined in the future.
Description
Keywords
biological sciences, drosophila