Modeling Congenital Disorders of N-Linked Glycoprotein Glycosylation in Drosophila melanogaster

Abstract

Protein glycosylation, the enzymatic addition of N-linked or O-linked glycans to proteins, serves crucial functions in animal cells and requires the action of glycosyltransferases, glycosidases and nucleotide-sugar transporters, localized in the endoplasmic reticulum and Golgi apparatus. Congenital Disorders of Glycosylation (CDGs) comprise a family of multisystemic diseases caused by mutations in genes encoding proteins involved in glycosylation pathways. CDGs are classified into two large groups. Type I CDGs affect the synthesis of the dolichol-linked Glc3Man9GlcNac2 precursor of N-linked glycosylation or its transfer to acceptor proteins. Type II CDG (CDG-II) diseases impair either the trimming of the N-linked oligosaccharide, the addition of terminal glycans or the biosynthesis of O-linked oligosaccharides, which occur in the Golgi apparatus. So far, over 100 distinct forms of CDGs are known, with the majority of them characterized by neurological defects including mental retardation, seizures and hypotonia. Yet, it is unclear how defective glycosylation causes the pathology of CDGs. This issue can be only addressed by developing animal models of specific CDGs. Drosophila melanogaster is emerging as a highly suitable organism for analyzing glycan-dependent functions in the central nervous system (CNS) and the involvement of N-glycosylation in neuropathologies. In this review we illustrate recent work that highlights the genetic and neurobiologic advantages offered by D. melanogaster for dissecting glycosylation pathways and modeling CDG pathophysiology.

CNS Glycosylphosphatidylinositol Deficiency Results in Delayed White Matter Development, Ataxia, and Premature Death in a Novel Mouse Model

“…We also found severe defects in motor coordination and striking defects in Purkinje cell arborization in the mosaic cKO cerebellum. Similar ataxic phenotypes and reduced lifespan have been observed in other models of CDG including the genetic reductions of Pmm2, Cog7, and Atp6ap2 in Drosophila models demonstrating that motor coordination critically requires normal glycosylation through phylogeny [32]. We found gene expression was significantly different in mosaic cKO mice compared to controls with an overexpression of tyrosine hydroxylase, a marker of premature cerebellar development.…”

Invivo and systematic analysis of random multigenic deletions associated with human diseases during epithelial morphogenesis in Drosophila

“…The cytoskeletal defect produced was similar to that produced by the deficiency line Df(1)Exel6242(BDSC-7716) (Figure 12(B-C)) and therefore we can suggest that the critical region for the epithelial defect is because of the gene α1,6-fucosyltransferase (FucT6) localized to 10D5-10D5. FucT6 is an uncharacterized gene suggested to be involved in N-glycan Fucosylation and N-linked glycosylation (Roos et al, 2002; Paschinger et al, 2005; Frappaolo et al, 2018). Similarly for overlapping regions, using deficiency lines Df(1)Exel6226(BDSC-7703) at 1E3-1F3 that generated on average only 12 clones and Df(1)ED6521(BDSC-9281) at 1E3-1F4 that generated 46 clones on an average, we have identified the critical region encoding a previously uncharacterized gene as N(alpha)acetyltransferase 30A (Naa30A) localized at 1F3-1F4.…”

“…The cytoskeletal defect produced was similar to that produced by the deficiency line Df(1)Exel6242(BDSC-7716) (Figure 12(B-C)) and therefore we can suggest that the critical region for the epithelial defect is because of the gene 1,6fucosyltransferase (FucT6) localized to 10D5-10D5. FucT6 is an uncharacterized gene suggested to be involved in N-glycan Fucosylation and N-linked glycosylation (Roos et al, 2002;Paschinger et al, 2005;Frappaolo et al, 2018).…”

The Close Relationship between the Golgi Trafficking Machinery and Protein Glycosylation

“…We may expect that the potential impact of mutations in some secretory trafficking players on glycosylation is so severe that it is not compatible with viability. Studies on model organisms (e.g., zebrafish, flies, mice) provide a valuable resource with which to dissect the phenotypic consequences of glycosylation disfunction in the whole organism and to identify potential therapeutic strategies for CDGs or cancer aimed at modulating secretory trafficking pathways [ 152 ].…”