Drosophila Neuroglian (Nrg), a homolog of vertebrate L1, is a prime example of a multifunctional cell adhesion molecule with a multiplicity of binding partners. Several types of single point mutations at different sites in human L1 have been shown to cause a variety of neurological disorders (CRASH syndrome) including mental retardation, hydrocephalus and spasticity. Nrg/L1 has been shown to be involved in axon pathfinding, neurite extension and cell migration. The role of Nrg/L1 in these developmental processes has been well-characterized in vertebrates and invertebrates but much less is known about potential functions during synapse formation. We have recently shown that Nrg does indeed have an essential function in synaptogenesis. We found that a single missense mutation in the extracellular domain of the nrg849 allele disrupts the assembly and functionality of a central synapse in a well- characterized neuronal circuit, the Giant Fiber System (GFS). Our data suggests that phosphorylation of the intracellular ankyrin binding motif of Nrg/L1 is crucial for giant synapse formation. Interestingly, human L1 is able to completely rescue the phenotype in nrg849 mutants while tested paralogs Neurofascin and NrCAM can not, despite having the same overall domain structure inclusive of the highly conserved ankyrin binding motif. This shows that the GFS is a valid model system for studying L1-specific function. Our preliminary studies indicate that some of the pathological missense mutations identified in L1 affect synapse formation rather than earlier developmental processes. Though a defect in neurite outgrowth, guidance or synapse formation may all result functionally in the same discernable phenotype, a disrupted connection between neurons, the biological process affected is completely different. Our data also suggests that some mutations do not result in a loss of a function phenotype but can also have gain of function and dominant negative consequences as well. Information about the particular biological process being disrupted as well as the protein function being compromised is crucial to find appropriate treatment plans for clinical pathologies associated with different types of mutations in the future. Hence, this grant is designed to further explore Nrg and L1's role in synapse formation as well as to study the effects of identified human mutations in L1 in vivo at a single cell level. We will combine the enormous resource of identified human L1 mutations and the power of genetic and molecular tools in Drosophila to determine which extracellular L1/Nrg interactions and intracellular signaling pathways play a role in synapse formation. We will determine the function of various L1/Nrg constructs in wild type, nrg849 and a temporal loss of function background electrophysiologically and anatomically. The knowledge gained from studies listed in this proposal will enable us to have a better understanding of the mechanisms involved in synaptogenesis as well as the cellular basis of the pathologies underlying L1-related neurological disorders. More than 170 different mutations in the cell adhesion molecule L1 have been identified to result in a variety of human neurological disorders which are associated with mental retardation, hydrocephalus (enlarged head due to collection of fluid on the brain) and spasticity (involuntary contraction of muscles). We intend to study the effects of these various pathological mutations in vivo at a single cell level in a unique model system, which will allow us to identify the particular biological process being affected, as well as the protein function being disrupted by the mutation. This information is essential to find appropriate treatment for the clinical manifestations of these mutations and hence will benefit the health of patients with L1-related disorders in the future.

National Institute of Health (NIH)
Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD)
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Synapses, Cytoskeleton and Trafficking Study Section (SYN)
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Henken, Deborah B
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Florida Atlantic University
Schools of Arts and Sciences
Boca Raton
United States
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Kudumala, Sirisha R; Penserga, Tyrone; Börner, Jana et al. (2017) Lissencephaly-1 dependent axonal retrograde transport of L1-type CAM Neuroglian in the adult drosophila central nervous system. PLoS One 12:e0183605
Lee, LaTasha H; Godenschwege, Tanja A (2015) Structure-function analyses of tyrosine phosphatase PTP69D in giant fiber synapse formation of Drosophila. Mol Cell Neurosci 64:24-31
Ermanoska, Biljana; Motley, William W; Leitão-Gonçalves, Ricardo et al. (2014) CMT-associated mutations in glycyl- and tyrosyl-tRNA synthetases exhibit similar pattern of toxicity and share common genetic modifiers in Drosophila. Neurobiol Dis 68:180-9
Mejia, Monica; Heghinian, Mari D; Mari, Frank et al. (2013) New tools for targeted disruption of cholinergic synaptic transmission in Drosophila melanogaster. PLoS One 8:e64685
Enneking, Eva-Maria; Kudumala, Sirisha R; Moreno, Eliza et al. (2013) Transsynaptic coordination of synaptic growth, function, and stability by the L1-type CAM Neuroglian. PLoS Biol 11:e1001537
Kudumala, Sirisha; Freund, Julie; Hortsch, Michael et al. (2013) Differential effects of human L1CAM mutations on complementing guidance and synaptic defects in Drosophila melanogaster. PLoS One 8:e76974
Boerner, Jana; Godenschwege, Tanja A (2011) Whole mount preparation of the adult Drosophila ventral nerve cord for giant fiber dye injection. J Vis Exp :
Kim, Chul; Srivastava, Sapeckshita; Rice, Marian et al. (2011) Expression of human amyloid precursor protein in the skeletal muscles of Drosophila results in age- and activity-dependent muscle weakness. BMC Physiol 11:7
Boerner, Jana; Godenschwege, Tanja Angela (2010) Application for the Drosophila ventral nerve cord standard in neuronal circuit reconstruction and in-depth analysis of mutant morphology. J Neurogenet 24:158-67
Allen, Marcus J; Godenschwege, Tanja A (2010) Electrophysiological recordings from the Drosophila giant fiber system (GFS). Cold Spring Harb Protoc 2010:pdb.prot5453

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