Synaptic roles for phosphomannomutase type 2 in a new Drosophila congenital disorder of glycosylation disease model

Abstract

Congenital disorders of glycosylation (CDGs) constitute a rapidly growing family of human diseases resulting from heritable mutations in genes driving the production and modification of glycoproteins. The resulting symptomatic hypoglycosylation causes multisystemic defects that include severe neurological impairments, revealing a particularly critical requirement for tightly regulated glycosylation in the nervous system. The most common CDG, CDG-Ia (PMM2-CDG), arises from phosphomannomutase type 2 (PMM2) mutations. Here, we report the generation and characterization of the first Drosophila CDG-Ia model. CRISPR-generated pmm2-null Drosophila mutants display severely disrupted glycosylation and early lethality, whereas RNAi-targeted knockdown of neuronal PMM2 results in a strong shift in the abundance of pauci-mannose glycan, progressive incoordination and later lethality, closely paralleling human CDG-Ia symptoms of shortened lifespan, movement impairments and defective neural development. Analyses of the well-characterized Drosophila neuromuscular junction (NMJ) reveal synaptic glycosylation loss accompanied by defects in both structural architecture and functional neurotransmission. NMJ synaptogenesis is driven by intercellular signals that traverse an extracellular synaptomatrix and are co-regulated by glycosylation and matrix metalloproteinases (MMPs). Specifically, trans-synaptic signaling by the Wnt protein Wingless (Wg) depends on the heparan sulfate proteoglycan (HSPG) co-receptor Dally-like protein (Dlp), which is regulated by synaptic MMP activity. Loss of synaptic MMP2, Wg ligand, Dlp co-receptor and downstream trans-synaptic signaling occurs with PMM2 knockdown. Taken together, this Drosophila CDG disease model provides a new avenue for the dissection of cellular and molecular mechanisms underlying neurological impairments and is a means by which to discover and test novel therapeutic treatment strategies.

Multifarious Functions of the Fragile X Mental Retardation Protein

“…Interestingly, neuronal FMRP regulates synaptic matrix metalloproteinase (MMP) classes in Drosophila , which sculpt intercellular signaling via proteolytic cleavage of extracellular proteins [63,64,65]. In the Drosophila FXS model, MMP levels are elevated, resulting in altered intercellular signaling, including trans -synaptic Wnt signaling [66,67]. This mechanism depends on regulation of the cell surface Wnt co-receptor Heparan Sulfate Proteoglycan (HSPG) Dally-like Protein (Dlp).…”

Secreted tissue inhibitor of matrix metalloproteinase restricts trans-synaptic signaling to coordinate synaptogenesis

“…Intercellular trans-synaptic signaling acts as a core modulator of NMJ structure, function and motor output, including regulation of bouton number, synaptic vesicle cycling and coordinated muscle motor function (JumboLucioni et al, 2016;Parkinson et al, 2016;Wu et al, 2010). Furthermore, our recent studies have revealed highly aberrant transsynaptic signaling in mmp1 and mmp2 mutants , and within the Mmp-dependent FXS disease model (Friedman et al, 2013).…”

Large-scale transgenicDrosophilaresource collections for loss- and gain-of-function studies

“…Mutant animals or tissue-specific mosaics can be produced by simply crossing sgRNA-expressing flies to germline-specific Cas9 or somatic tissuespecific GAL4>Cas9 flies, respectively (Kondo and Ueda 2013;Port et al 2014;Port and Bullock 2016). A number of recent studies in Drosophila have used transgenic CRISPR for LOF, for example to identify novel modifiers of tauopathies (Butzlaff et al 2015;Dourlen et al 2017) or Parkinson's disease (Chen et al 2017;Rousseaux et al 2018); to model congenital disorders of glycosylation (Parkinson et al 2016); to identify genes that regulate tumorigenesis (Das et al 2013;Mishra-Gorur et al 2019); and to study inflammation and immunity (Lee et al 2018;Liu et al 2018).…”