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author:("Li, wane")
1.  Imaging a Population Code for Odor Identity in the Drosophila Mushroom Body 
The Journal of Neuroscience  2013;33(25):10568-10581.
The brain represents sensory information in the coordinated activity of neuronal ensembles. Although the microcircuits underlying olfactory processing are well characterized in Drosophila, no studies to date have examined the encoding of odor identity by populations of neurons and related it to the odor specificity of olfactory behavior. Here we used two-photon Ca2+ imaging to record odor-evoked responses from >100 neurons simultaneously in the Drosophila mushroom body (MB). For the first time, we demonstrate quantitatively that MB population responses contain substantial information on odor identity. Using a series of increasingly similar odor blends, we identified conditions in which odor discrimination is difficult behaviorally. We found that MB ensemble responses accounted well for olfactory acuity in this task. Kenyon cell ensembles with as few as 25 cells were sufficient to match behavioral discrimination accuracy. Using a generalization task, we demonstrated that the MB population code could predict the flies' responses to novel odors. The degree to which flies generalized a learned aversive association to unfamiliar test odors depended upon the relative similarity between the odors' evoked MB activity patterns. Discrimination and generalization place different demands on the animal, yet the flies' choices in these tasks were reliably predicted based on the amount of overlap between MB activity patterns. Therefore, these different behaviors can be understood in the context of a single physiological framework.
PMCID: PMC3685844  PMID: 23785169
2.  A Prion-mediated Mechanism for Memory Proposed in Drosophila 
Neuron  2012;76(2):260-262.
Memories are remarkably persistent, but rely on transient signaling. The prion-like properties of CPEB suggested a solution to this problem. The paper by Krüttner et al demonstrates that the prion-like domain of Drosophila CPEB functions independently of its RNA binding domain for memory.
PMCID: PMC3488862  PMID: 23083729
3.  microRNA-276a Functions in Ellipsoid Body and Mushroom Body Neurons for Naïve and Conditioned Olfactory Avoidance in Drosophila 
microRNA-mediated gene regulation plays a key role in brain development and function. But there are few cases in which the roles of individual miRNAs have been elucidated in behaving animals. We report a miR-276a::DopR regulatory module in Drosophila that functions in distinct circuits for naïve odor responses and conditioned odor memory. Drosophila olfactory aversive memory involves convergence of the odors (conditioned stimulus, CS) and the electric shock (unconditioned stimulus, US) in mushroom body (MB) neurons. Dopamine receptor, DopR, mediates the US inputs onto MB. Distinct dopaminergic neurons also innervate ellipsoid body (EB), where DopR function modulates arousal to external stimuli. We demonstrate that miR-276a is required in MB neurons for memory formation and in EB for naïve responses to odors. Both roles of miR-276a are mediated by tuning DopR expression. The dual role of this miR-276a::DopR genetic module in these two neural circuits highlights the importance of miRNA-mediated gene regulation within distinct circuits underlying both naïve behavioral responses and memory.
PMCID: PMC3640307  PMID: 23536094
4.  Transposable Elements in TDP-43-Mediated Neurodegenerative Disorders 
PLoS ONE  2012;7(9):e44099.
Elevated expression of specific transposable elements (TEs) has been observed in several neurodegenerative disorders. TEs also can be active during normal neurogenesis. By mining a series of deep sequencing datasets of protein-RNA interactions and of gene expression profiles, we uncovered extensive binding of TE transcripts to TDP-43, an RNA-binding protein central to amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). Second, we find that association between TDP-43 and many of its TE targets is reduced in FTLD patients. Third, we discovered that a large fraction of the TEs to which TDP-43 binds become de-repressed in mouse TDP-43 disease models. We propose the hypothesis that TE mis-regulation contributes to TDP-43 related neurodegenerative diseases.
PMCID: PMC3434193  PMID: 22957047
5.  Short and Long-term memory in Drosophila require cAMP signaling in distinct neuron types 
Current biology : CB  2009;19(16):1341-1350.
A common feature of memory and its underlying synaptic plasticity is that each can be dissected into short-lived forms involving modification or trafficking of existing proteins and long-term forms that require new gene expression. An underlying assumption of this cellular view of memory consolidation is that these different mechanisms occur within a single neuron. At the neuro-anatomical level, however, different temporal stages of memory can engage distinct neural circuits, a notion that has not been conceptually integrated with the cellular view.
We have investigated this issue in the context of aversive Pavlovian olfactory memory in Drosophila. Previous studies have demonstrated a central role for cAMP signaling in the mushroom body (MB). The Ca++ responsive adenylyl cyclase rutabaga is believed to be a coincidence detector in γ neurons, one of the three principle classes of MB Kenyon cells. We are able to separately restore short-term or long-term memory to a rutabaga mutant with expression of rutabaga in different subsets of MB neurons.
Our findings suggest a model in which the learning experience initiates two parallel associations: a short-lived trace in MB γ neurons, and a long-lived trace in α/β neurons.
PMCID: PMC2752374  PMID: 19646879
6.  Identification of Synaptic Targets of Drosophila Pumilio 
PLoS Computational Biology  2008;4(2):e1000026.
Drosophila Pumilio (Pum) protein is a translational regulator involved in embryonic patterning and germline development. Recent findings demonstrate that Pum also plays an important role in the nervous system, both at the neuromuscular junction (NMJ) and in long-term memory formation. In neurons, Pum appears to play a role in homeostatic control of excitability via down regulation of para, a voltage gated sodium channel, and may more generally modulate local protein synthesis in neurons via translational repression of eIF-4E. Aside from these, the biologically relevant targets of Pum in the nervous system remain largely unknown. We hypothesized that Pum might play a role in regulating the local translation underlying synapse-specific modifications during memory formation. To identify relevant translational targets, we used an informatics approach to predict Pum targets among mRNAs whose products have synaptic localization. We then used both in vitro binding and two in vivo assays to functionally confirm the fidelity of this informatics screening method. We find that Pum strongly and specifically binds to RNA sequences in the 3′UTR of four of the predicted target genes, demonstrating the validity of our method. We then demonstrate that one of these predicted target sequences, in the 3′UTR of discs large (dlg1), the Drosophila PSD95 ortholog, can functionally substitute for a canonical NRE (Nanos response element) in vivo in a heterologous functional assay. Finally, we show that the endogenous dlg1 mRNA can be regulated by Pumilio in a neuronal context, the adult mushroom bodies (MB), which is an anatomical site of memory storage.
Author Summary
The Drosophila Pumilio (Pum) protein was originally identified as a translational control factor for embryo patterning. Subsequent studies have identified Pum's role in multiple biological processes, including the maintenance of germline stem cell, the proliferation and migration of primordial germ cells, olfactory leaning and memory, and synaptic plasticity. Pum is highly conserved across phyla, i.e., from worm to human; however, the mRNA targets of Pum within each tissue and organism are largely unknown. On the other hand, the prediction of RNA binding sites remains a hard question in the computational field. We were interested in finding Pum targets in the nervous system using fruit flies as a model organism. To accomplish this, we used the few Pum binding sequences that had previously been shown in vivo as “training sequences” to construct bioinformatic models of the Pum binding site. We then predicted a few Pum mRNA targets among the genes known to function in neuronal synapses. We then used a combination of “golden standards” to verify these predictions: a biochemical assay called gel shifts, and in vivo functional assays both in embryo and neurons. With these approaches, we successfully confirmed one of the targets as Dlg, which is the Drosophila ortholog of human PSD95. Therefore, we present a complete story from computational study to real biological functions.
PMCID: PMC2265480  PMID: 18463699

Results 1-6 (6)