This research program investigates interactive roles of secreted signals and extracellular matrix proteoglycans in the development of neuromuscular junction (NMJ) synapses. Our long-term strategy has been to use Drosophila forward genetic screens to identify new genes and characterize novel mechanisms driving embryonic synaptogenesis and the differentiation of synaptic function. Numerous genetic mutants discovered over the last five years provide the foundation of this proposal, by highlighting the importance of extracellular glycosylation and proteolytic mechanisms shaping trans-synaptic signaling. The multiple interacting proteins we focus on in the proposal include: 1) Heparan Sulfate (HS) 6-O-sulfotransferase Hs6st and 2) HS 6-O-sulfatase Sulf1, two functionally-paired enzymes acting on the same N-sulfoglucosamine C6 carbon;3) the secreted Jelly Belly (Jeb) trans-synaptic signal binding to the 4) Anaplastic Lymphoma Kinase (Alk) receptor tyrosine kinase, both of which are regulated by 5) GlcNAc Transferase 1 (Mgat1) and 6) secreted Mind-the-Gap (Mtg) lectin for N-acetylglucosamine (GlcNAc)-proteoglycans;and 7) secreted matrix metalloproteinase (MMP) and tissue inhibitor of MMP (TIMP), both of which genetically interact with 8) Fragile X Mental Retardation Protein (FMRP) in regulating synaptogenesis. From this fertile foundation, we propose to focus intensively on the extracellular glycobiology of intercellular interactions driving NMJ development. Our core hypothesis is that extracellular glycans function as staging platforms that bind and combinatorially modulate multiple trans-synaptic signals driving synaptogenesis. We propose three specific aims to test this hypothesis.
In Aim I, we use sulf1/hs6st mutants as a tool to investigate the roles of Heparan Sulfate Proteoglycan (HSPG) mechanisms in WNT (Wingless, Wg)/TGFb/BMP (Glass Bottom Boat, Gbb) trans-synaptic signaling.
In Aim II, we test extracellular N-glycan mechanisms in regulation of the newly-defined Jeb-Alk trans-synaptic signaling, as well as interactions with the Wg and Gbb pathways.
In Aim III, we test roles of MMPs and TIMP in synaptic ECM remodeling, in conjunction with FMRP synaptogenic requirements. We will test how this mechanism regulates HSPGs to control the combinatorial trans-synaptic signaling of Jeb, Wg and Gbb ligands. This work has direct relevance for numerous neuromuscular and neurological diseases, including Congenital Disorders of Glycosylation (CDG) and Fragile X syndrome (FXS), the leading heritable cause of cognitive impairment and autism spectrum disorders.

Public Health Relevance

Heavily glycosylated extracellular matrix, membrane-anchored and transmembrane proteins play critical roles in shaping intercellular signals driving synapse formation. Defects in these intercellular interactions are linked to neurological disorders caused by neuromuscular (muscular dystrophies) and cognitive (mental retardation) synaptic impairments. This research program utilizes the powerful Drosophila genetic system to identify new genes and molecular mechanisms critical for establishing the extracellular environment to control intercellular signaling events during synaptogenesis.

National Institute of Health (NIH)
National Institute of Mental Health (NIMH)
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Synapses, Cytoskeleton and Trafficking Study Section (SYN)
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Asanuma, Chiiko
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Vanderbilt University Medical Center
Schools of Arts and Sciences
United States
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Kopke, Danielle L; Broadie, Kendal (2018) FM Dye Cycling at the Synapse: Comparing High Potassium Depolarization, Electrical and Channelrhodopsin Stimulation. J Vis Exp :
Dear, Mary L; Shilts, Jarrod; Broadie, Kendal (2017) Neuronal activity drives FMRP- and HSPG-dependent matrix metalloproteinase function required for rapid synaptogenesis. Sci Signal 10:
Sears, James C; Broadie, Kendal (2017) Fragile X Mental Retardation Protein Regulates Activity-Dependent Membrane Trafficking and Trans-Synaptic Signaling Mediating Synaptic Remodeling. Front Mol Neurosci 10:440
Shilts, Jarrod; Broadie, Kendal (2017) Secreted tissue inhibitor of matrix metalloproteinase restricts trans-synaptic signaling to coordinate synaptogenesis. J Cell Sci 130:2344-2358
Kopke, Danielle L; Lima, Sofia C; Alexandre, Cyrille et al. (2017) Notum coordinates synapse development via extracellular regulation of Wingless trans-synaptic signaling. Development 144:3499-3510
Jumbo-Lucioni, Patricia P; Parkinson, William M; Kopke, Danielle L et al. (2016) Coordinated movement, neuromuscular synaptogenesis and trans-synaptic signaling defects in Drosophila galactosemia models. Hum Mol Genet 25:3699-3714
Dear, Mary Lynn; Dani, Neil; Parkinson, William et al. (2016) Two classes of matrix metalloproteinases reciprocally regulate synaptogenesis. Development 143:75-87
Parkinson, William M; Dookwah, Michelle; Dear, Mary Lynn et al. (2016) Synaptic roles for phosphomannomutase type 2 in a new Drosophila congenital disorder of glycosylation disease model. Dis Model Mech 9:513-27
Jumbo-Lucioni, Patricia; Parkinson, William; Broadie, Kendal (2014) Overelaborated synaptic architecture and reduced synaptomatrix glycosylation in a Drosophila classic galactosemia disease model. Dis Model Mech 7:1365-78
Dani, Neil; Zhu, He; Broadie, Kendal (2014) Two protein N-acetylgalactosaminyl transferases regulate synaptic plasticity by activity-dependent regulation of integrin signaling. J Neurosci 34:13047-65

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