Honors & Awards
Stanford University Postdoctoral Research Award, SUPD (2012)
K99/R00 Pathway to Independence Award, NIH / NIDCD (2013-2018)
Boards, Advisory Committees, Professional Organizations
Member, Society for Neuroscience (2003 - Present)
Doctor of Philosophy, Harvard University (2009)
Master of Science, Yale University (2003)
Bachelor of Science, Yale University (2003)
Liqun Luo, Postdoctoral Faculty Sponsor
Current Research and Scholarly Interests
The synapse is the fundamental unit of neuronal communication; determining the organizational and molecular logic underlying synaptogenesis is paramount to understanding how the brain develops, how neural circuits form, and how neural disorder proceeds. My work seeks to understand the molecular mechanisms involved in proper synaptic development and how these synapses interact within a circuit.
On the Teneurin track: a new synaptic organization molecule emerges
FRONTIERS IN CELLULAR NEUROSCIENCE
To achieve proper synaptic development and function, coordinated signals must pass between the pre- and postsynaptic membranes. Such transsynaptic signals can be comprised of receptors and secreted ligands, membrane associated receptors, and also pairs of synaptic cell adhesion molecules. A critical open question bridging neuroscience, developmental biology, and cell biology involves identifying those signals and elucidating how they function. Recent work in Drosophila and vertebrate systems has implicated a family of proteins, the Teneurins, as a new transsynaptic signal in both the peripheral and central nervous systems. The Teneurins have established roles in neuronal wiring, but studies now show their involvement in regulating synaptic connections between neurons and bridging the synaptic membrane and the cytoskeleton. This review will examine the Teneurins as synaptic cell adhesion molecules, explore how they regulate synaptic organization, and consider how some consequences of human Teneurin mutations may have synaptopathic origins.
View details for DOI 10.3389/fincel.2015.00204
View details for Web of Science ID 000357522500001
View details for PubMedID 26074772
- Synaptic organization of the Drosophila antennal lobe and its regulation by the Teneurins ELIFE 2014; 3
Plum, an immunoglobulin superfamily protein, regulates axon pruning by facilitating TGF-ß signaling.
2013; 78 (3): 456-468
Axon pruning during development is essential for proper wiring of the mature nervous system, but its regulation remains poorly understood. We have identified an immunoglobulin superfamily (IgSF) transmembrane protein, Plum, that is cell autonomously required for axon pruning of mushroom body (MB) γ neurons and for ectopic synapse refinement at the developing neuromuscular junction in Drosophila. Plum promotes MB γ neuron axon pruning by regulating the expression of Ecdysone Receptor-B1, a key initiator of axon pruning. Genetic analyses indicate that Plum acts to facilitate signaling of Myoglianin, a glial-derived TGF-β, on MB γ neurons upstream of the type-I TGF-β receptor Baboon. Myoglianin, Baboon, and Ecdysone Receptor-B1 are also required for neuromuscular junction ectopic synapse refinement. Our study highlights both IgSF proteins and TGF-β facilitation as key promoters of developmental axon elimination and demonstrates a mechanistic conservation between MB axon pruning during metamorphosis and the refinement of ectopic larval neuromuscular connections.
View details for DOI 10.1016/j.neuron.2013.03.004
View details for PubMedID 23664613
Teneurins instruct synaptic partner matching in an olfactory map
2012; 484 (7393): 201-U82
Neurons are interconnected with extraordinary precision to assemble a functional nervous system. Compared to axon guidance, far less is understood about how individual pre- and postsynaptic partners are matched. To ensure the proper relay of olfactory information in the fruitfly Drosophila, axons of ?50 classes of olfactory receptor neurons (ORNs) form one-to-one connections with dendrites of ?50 classes of projection neurons (PNs). Here, using genetic screens, we identified two evolutionarily conserved, epidermal growth factor (EGF)-repeat containing transmembrane Teneurin proteins, Ten-m and Ten-a, as synaptic-partner-matching molecules between PN dendrites and ORN axons. Ten-m and Ten-a are highly expressed in select PN-ORN matching pairs. Teneurin loss- and gain-of-function cause specific mismatching of select ORNs and PNs. Finally, Teneurins promote homophilic interactions in vitro, and Ten-m co-expression in non-partner PNs and ORNs promotes their ectopic connections in vivo. We propose that Teneurins instruct matching specificity between synaptic partners through homophilic attraction.
View details for DOI 10.1038/nature10926
View details for Web of Science ID 000303149900027
View details for PubMedID 22425994
Trans-synaptic Teneurin signalling in neuromuscular synapse organization and target choice
2012; 484 (7393): 237-U122
Synapse assembly requires trans-synaptic signals between the pre- and postsynapse, but our understanding of the essential organizational molecules involved in this process remains incomplete. Teneurin proteins are conserved, epidermal growth factor (EGF)-repeat-containing transmembrane proteins with large extracellular domains. Here we show that two Drosophila Teneurins, Ten-m and Ten-a, are required for neuromuscular synapse organization and target selection. Ten-a is presynaptic whereas Ten-m is mostly postsynaptic; neuronal Ten-a and muscle Ten-m form a complex in vivo. Pre- or postsynaptic Teneurin perturbations cause severe synapse loss and impair many facets of organization trans-synaptically and cell autonomously. These include defects in active zone apposition, release sites, membrane and vesicle organization, and synaptic transmission. Moreover, the presynaptic microtubule and postsynaptic spectrin cytoskeletons are severely disrupted, suggesting a mechanism whereby Teneurins organize the cytoskeleton, which in turn affects other aspects of synapse development. Supporting this, Ten-m physically interacts with ?-Spectrin. Genetic analyses of teneurin and neuroligin reveal that they have differential roles that synergize to promote synapse assembly. Finally, at elevated endogenous levels, Ten-m regulates target selection between specific motor neurons and muscles. Our study identifies the Teneurins as a key bi-directional trans-synaptic signal involved in general synapse organization, and demonstrates that proteins such as these can also regulate target selection.
View details for DOI 10.1038/nature10923
View details for Web of Science ID 000303149900034
View details for PubMedID 22426000
Drosophila Importin-alpha 2 Is Involved in Synapse, Axon and Muscle Development
2010; 5 (12)
Nuclear import is required for communication between the cytoplasm and the nucleus and to enact lasting changes in gene transcription following stimuli. Binding to an Importin-? molecule in the cytoplasm is often required to mediate nuclear entry of a signaling protein. As multiple isoforms of Importin-? exist, some may be responsible for the entry of distinct cargoes rather than general nuclear import. Indeed, in neuronal systems, Importin-? isoforms can mediate very specific processes such as axonal tiling and communication of an injury signal. To study nuclear import during development, we examined the expression and function of Importin-?2 in Drosophila melanogaster. We found that Importin-?2 was expressed in the nervous system where it was required for normal active zone density at the NMJ and axonal commissure formation in the central nervous system. Other aspects of synaptic morphology at the NMJ and the localization of other synaptic markers appeared normal in importin-?2 mutants. Importin-?2 also functioned in development of the body wall musculature. Mutants in importin-?2 exhibited errors in muscle patterning and organization that could be alleviated by restoring muscle expression of Importin-?2. Thus, Importin-?2 is needed for some processes in the development of both the nervous system and the larval musculature.
View details for DOI 10.1371/journal.pone.0015223
View details for Web of Science ID 000284995300022
View details for PubMedID 21151903
The nuclear import of Frizzled2-C by Importins-beta 11 and alpha 2 promotes postsynaptic development
2010; 13 (8): 935-U50
Synapse-to-nucleus signaling is critical for synaptic development and plasticity. In Drosophila, the ligand Wingless causes the C terminus of its Frizzled2 receptor (Fz2-C) to be cleaved and translocated from the postsynaptic density to nuclei. The mechanism of nuclear import is unknown and the developmental consequences of this translocation are uncertain. We found that Fz2-C localization to muscle nuclei required the nuclear import factors Importin-beta11 and Importin-alpha2 and that this pathway promoted the postsynaptic development of the subsynaptic reticulum (SSR), an elaboration of the postsynaptic plasma membrane. importin-beta11 (imp-beta11) and dfz2 mutants had less SSR, and some boutons lacked the postsynaptic marker Discs Large. These developmental defects in imp-beta11 mutants could be overcome by expression of Fz2-C fused to a nuclear localization sequence that can bypass Importin-beta11. Thus, Wnt-activated growth of the postsynaptic membrane is mediated by the synapse-to-nucleus translocation and active nuclear import of Fz2-C via a selective Importin-beta11/alpha2 pathway.
View details for DOI 10.1038/nn.2593
View details for Web of Science ID 000280400600011
View details for PubMedID 20601947
Importin-beta 11 Regulates Synaptic Phosphorylated Mothers Against Decapentaplegic, and Thereby Influences Synaptic Development and Function at the Drosophila Neuromuscular Junction
JOURNAL OF NEUROSCIENCE
2010; 30 (15): 5253-5268
Importin proteins act both at the nuclear pore to promote substrate entry and in the cytosol during signal trafficking. Here, we describe mutations in the Drosophila gene importin-beta11, which has not previously been analyzed genetically. Mutants of importin-beta11 died as late pupae from neuronal defects, and neuronal importin-beta11 was present not only at nuclear pores but also in the cytosol and at synapses. Neurons lacking importin-beta11 were viable and properly differentiated but exhibited discrete defects. Synaptic transmission was defective in adult photoreceptors and at larval neuromuscular junctions (NMJs). Mutant photoreceptor axons formed grossly normal projections and synaptic terminals in the brain, but synaptic arbors on larval muscles were smaller while still containing appropriate synaptic components. Bone morphogenic protein (BMP) signaling was the apparent cause of the observed NMJ defects. Importin-beta11 interacted genetically with the BMP pathway, and at mutant synaptic boutons, a key component of this pathway, phosphorylated mothers against decapentaplegic (pMAD), was reduced. Neuronal expression of an importin-beta11 transgene rescued this phenotype as well as the other observed neuromuscular phenotypes. Despite the loss of synaptic pMAD, pMAD persisted in motor neuron nuclei, suggesting a specific impairment in the local function of pMAD. Restoring levels of pMAD to mutant terminals via expression of constitutively active type I BMP receptors or by reducing retrograde transport in motor neurons also restored synaptic strength and morphology. Thus, importin-beta11 function interacts with the BMP pathway to regulate a pool of pMAD that must be present at the presynapse for its proper development and function.
View details for DOI 10.1523/JNEUROSCI.3739-09.2010
View details for Web of Science ID 000276685100014
View details for PubMedID 20392948
Dissection of synaptic excitability phenotypes by using a dominant-negative Shaker K+ channel subunit
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2005; 102 (9): 3477-3482
During nervous system development, synapses undergo morphological change as a function of electrical activity. In Drosophila, enhanced activity results in the expansion of larval neuromuscular junctions. We have examined whether these structural changes involve the pre- or postsynaptic partner by selectively enhancing electrical excitability with a Shaker dominant-negative (SDN) potassium channel subunit. We find that the SDN enhances neurotransmitter release when expressed in motoneurons, postsynaptic potential broadening when expressed in muscles and neurons, and selectively suppresses fast-inactivating, Shaker-mediated IA currents in muscles. SDN expression also phenocopies the canonical behavioral phenotypes of the Sh mutation. At the neuromuscular junction, we find that activity-dependent changes in arbor size occur only when SDN is expressed presynaptically. This finding indicates that elevated postsynaptic membrane excitability is by itself insufficient to enhance presynaptic arbor growth. Such changes must minimally involve increased neuronal excitability.
View details for DOI 10.1073/pnas.0406164102
View details for Web of Science ID 000227423700056
View details for PubMedID 15728380