N-glycosylation requirements in neuromuscular synaptogenesis.
Neural development requires N-glycosylation regulation of intercellular signaling, but the requirements in synaptogenesis have not been well tested. All complex and hybrid N-glycosylation requires MGAT1 (UDP-GlcNAc:α-3-D-mannoside-β1,2-N-acetylglucosaminyl-transferase I) function, and Mgat1 nulls are the most compromised N-glycosylation condition that survive long enough to permit synaptogenesis studies. At the Drosophila neuromuscular junction (NMJ), Mgat1 mutants display selective loss of lectin-defined carbohydrates in the extracellular synaptomatrix, and an accompanying accumulation of the secreted endogenous Mind the gap (MTG) lectin, a key synaptogenesis regulator. Null Mgat1 mutants exhibit strongly overelaborated synaptic structural development, consistent with inhibitory roles for complex/hybrid N-glycans in morphological synaptogenesis, and strengthened functional synapse differentiation, consistent with synaptogenic MTG functions. Synapse molecular composition is surprisingly selectively altered, with decreases in presynaptic active zone Bruchpilot (BRP) and postsynaptic Glutamate receptor subtype B (GLURIIB), but no detectable change in a wide range of other synaptic components. Synaptogenesis is driven by bidirectional trans-synaptic signals that traverse the glycan-rich synaptomatrix, and Mgat1 mutation disrupts both anterograde and retrograde signals, consistent with MTG regulation of trans-synaptic signaling. Downstream of intercellular signaling, pre- and postsynaptic scaffolds are recruited to drive synaptogenesis, and Mgat1 mutants exhibit loss of both classic Discs large 1 (DLG1) and newly defined Lethal (2) giant larvae [L(2)GL] scaffolds. We conclude that MGAT1-dependent N-glycosylation shapes the synaptomatrix carbohydrate environment and endogenous lectin localization within this domain, to modulate retention of trans-synaptic signaling ligands driving synaptic scaffold recruitment during synaptogenesis.
Department of Biological Sciences, Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, TN 37212, USA.
William
W
Parkinson
Mary Lynn
ML
Dear
Emma
E
Rushton
Kendal
K
Broadie
D000818:Animals; D030801:Animals, Genetically Modified; D002352:Carrier Proteins / Q000378:metabolism; D029721:Drosophila Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000196:embryology* / Q000378:metabolism; D006031:Glycosylation; D017351:N-Acetylglucosaminyltransferases / Q000235:genetics / Q000378:metabolism*; D009420:Nervous System / Q000196:embryology*; D055495:Neurogenesis; D009469:Neuromuscular Junction / Q000235:genetics / Q000378:metabolism; D018091:Receptors, AMPA / Q000096:biosynthesis; D015398:Signal Transduction; D013569:Synapses / Q000378:metabolism*; D009435:Synaptic Transmission / Q000235:genetics; D025521:Tumor Suppressor Proteins / Q000235:genetics
C510146:BRP protein, Drosophila; D002352:Carrier Proteins; D029721:Drosophila Proteins; D018091:Receptors, AMPA; D025521:Tumor Suppressor Proteins; C115953:glutamate receptor type B; C081435:l(2)gl protein, Drosophila; C540270:mtg protein, Drosophila; C070350:dlg1 protein, Drosophila; D017351:N-Acetylglucosaminyltransferases; C586339:MGAT1 protein, Drosophila
Active zone; Drosophila; Glutamate receptor; Neuromuscular junction; Synaptic scaffold; Synaptomatrix; Trans-synaptic signaling