Anne F. Simon

A single population of olfactory sensory neurons mediates an innate avoidance behaviour in Drosophila

All animals exhibit innate behaviours in response to specific sensory stimuli that are likely to result from the activation of developmentally programmed neural circuits. Here we observe that Drosophila exhibit robust avoidance to odours released by stressed flies. Gas chromatography and mass spectrometry identifies one component of this ‘Drosophila stress odorant (dSO)’ as CO2. CO2 elicits avoidance behaviour, at levels as low as 0.1%. We used two-photon imaging with the Ca2+-sensitive fluorescent protein G-CaMP to map the primary sensory neurons governing avoidance to CO2. CO2 activates only a single glomerulus in the antennal lobe, the V glomerulus; moreover, this glomerulus is not activated by any of 26 other odorants tested. Inhibition of synaptic transmission in sensory neurons that innervate the V glomerulus, using a temperature-sensitive Shibire gene (Shits), blocks the avoidance response to CO2. Inhibition of synaptic release in the vast majority of other olfactory receptor neurons has no effect on this behaviour. These data demonstrate that the activation of a single population of sensory neurons innervating one glomerulus is responsible for an innate avoidance behaviour in Drosophila.

The Drosophila putative kinase linotte (derailed) prevents central brain axons from converging on a newly described interhemispheric ring.

The lio gene encodes a putative receptor tyrosine kinase, with unique motifs both in the extracellular and catalytic domains (Dura, J.-M., Préat, T., Tully, T., 1993. Identification of linotte, a new gene affecting learning and memory in Drosophila melanogaster. J. Neurogenet. 9, 1-14). We show here that a complete deletion of lio activity causes specific structural defects in the adult brain. Gal4 enhancer-trap lines used as cell markers revealed that in lio mutants central brain axons behave as if they were abnormally attracted by the midbrain area. The Lio protein is expressed in third instar larvae in a few cells at the junction of the cerebral hemispheres. These glial cells form a newly described ring structure, showing an invariable fibrous organization. In the wild-type this ring disappears at midpupation. Our results indicate that the Lio putative kinase plays a major role in the modeling of the adult brain by controlling the fate of the transient interhemispheric ring.

The Drosophila vesicular monoamine transporter reduces pesticide-induced loss of dopaminergic neurons.

Dopamine is cytotoxic and may play a role in the development of Parkinsons disease. However, its interaction with environmental risk factors such as pesticides remains poorly understood. The vesicular monoamine transporter (VMAT) regulates intracellular dopamine content, and we have tested the neuroprotective effects of VMAT in vivo using the model organism Drosophila melanogaster. We find that Drosophila VMAT (dVMAT) mutants contain fewer dopaminergic neurons than wild type, consistent with a developmental effect, and that dopaminergic cell loss in the mutant is exacerbated by the pesticides rotenone and paraquat. Overexpression of DVMAT protein does not increase the survival of animals exposed to rotenone, but blocks the loss of dopaminergic neurons caused by this pesticide. These results are the first to demonstrate an interaction between a VMAT and pesticides in vivo, and provide an important model to investigate the mechanisms by which pesticides and cellular DA may interact to kill dopaminergic cells.

A simple assay to study social behavior in Drosophila: measurement of social space within a group

We have established a new simple behavioral paradigm in Drosophila melanogaster to determine how genes and the environment influence the behavior of flies within a social group. Specifically, we measure social space as the distance between two flies. The majority of Canton‐s flies, regardless of their gender, are within two body lengths from each other. Their social experience affects this behavior, with social isolation reducing and mating enhancing social space respectively, in both males and females. Unlike several other social behaviors in the fly, including the formation of social groups themselves (a well‐described behavior), social space does not require the perception of the previously identified aggregation pheromone cis‐vaccenyl acetate. Conversely, performance of the assay in darkness or mutations in the eye pigmentation gene white increased social space. Our results establish a new assay for the genetic dissection of a fundamental mode of social interaction.

A glial variant of the vesicular monoamine transporter is required to store histamine in the Drosophila visual system.

Unlike other monoamine neurotransmitters, the mechanism by which the brains histamine content is regulated remains unclear. In mammals, vesicular monoamine transporters (VMATs) are expressed exclusively in neurons and mediate the storage of histamine and other monoamines. We have studied the visual system of Drosophila melanogaster in which histamine is the primary neurotransmitter released from photoreceptor cells. We report here that a novel mRNA splice variant of Drosophila VMAT (DVMAT-B) is expressed not in neurons but rather in a small subset of glia in the lamina of the flys optic lobe. Histamine contents are reduced by mutation of dVMAT, but can be partially restored by specifically expressing DVMAT-B in glia. Our results suggest a novel role for a monoamine transporter in glia that may be relevant to histamine homeostasis in other systems.

Drosophila Vesicular Monoamine Transporter Mutants Can Adapt to Reduced or Eliminated Vesicular Stores of Dopamine and Serotonin

Physiologic and pathogenic changes in amine release induce dramatic behavioral changes, but the underlying cellular mechanisms remain unclear. To investigate these adaptive processes, we have characterized mutations in the Drosophila vesicular monoamine transporter (dVMAT), which is required for the vesicular storage of dopamine, serotonin, and octopamine. dVMAT mutant larvae show reduced locomotion and decreased electrical activity in motoneurons innervating the neuromuscular junction (NMJ) implicating central amines in the regulation of these activities. A parallel increase in evoked glutamate release by the motoneuron is consistent with a homeostatic adaptation at the NMJ. Despite the importance of aminergic signaling for regulating locomotion and other behaviors, adult dVMAT homozygous null mutants survive under conditions of low population density, thus allowing a phenotypic characterization of adult behavior. Homozygous mutant females are sterile and show defects in both egg retention and development; males also show reduced fertility. Homozygotes show an increased attraction to light but are mildly impaired in geotaxis and escape behaviors. In contrast, heterozygous mutants show an exaggerated escape response. Both hetero- and homozygous mutants demonstrate an altered behavioral response to cocaine. dVMAT mutants define potentially adaptive responses to reduced or eliminated aminergic signaling and will be useful to identify the underlying molecular mechanisms.

Effect of bisphenol A on Drosophila melanogaster behavior--a new model for the studies on neurodevelopmental disorders.

Developmental disorders such as autism and attention deficit hyperactivity disorder (ADHD) appear to have a complex etiology implicating both genetic and environmental factors. Bisphenol A (BPA), a widely used chemical in the plastic containers and in the linings of food and beverage cans, has been suggested to play a possible causative role in some developmental disorders. Here, we report behavioral modifications in Drosophila melanogaster following early exposure to BPA, which may suggest BPA as an environmental risk factor for the behavioral impairments that are the basis of diagnosis of autism and ADHD. In an open field assay with perinatally BPA-exposed and vehicle-treated control Drosophila, different parameters of locomotion (distance traveled, walking speed, spatial movement, mobility, turn angle, angular velocity and meander) were analyzed using the ethovision software. We also examined the repetitive and social interaction behaviors in these flies. In an open field assay, we identified disturbances in the locomotion patterns of BPA-exposed Drosophila that may relate to the decision-making and the motivational state of the animal. An increase in repetitive behavior was observed as an increase in the grooming behavior of Drosophila following BPA exposure. Furthermore, we also observed abnormal social interaction by the BPA-exposed flies in a social setting. These results demonstrate the effect of the environmentally prevalent risk agent BPA on the behavior of Drosophila, and suggest the practicability and the ease of using Drosophila as a model in the studies of neurobehavioral developmental disorders.

Drosophila mutants of the autism candidate gene neurobeachin (rugose) exhibit neuro-developmental disorders, aberrant synaptic properties, altered locomotion, and impaired adult social behavior and activity patterns.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder in humans characterized by complex behavioral deficits, including intellectual disability, impaired social interactions, and hyperactivity. ASD exhibits a strong genetic component with underlying multigene interactions. Candidate gene studies have shown that the neurobeachin (NBEA) gene is disrupted in human patients with idiopathic autism (Castermans et al., 2003). The NBEA gene spans the common fragile site FRA 13A and encodes a signal scaffold protein (Savelyeva et al., 2006). In mice, NBEA has been shown to be involved in the trafficking and function of a specific subset of synaptic vesicles. (Medrihan et al., 2009; Savelyeva et al., 2006). Rugose (rg) is the Drosophila homolog of the mammalian and human NBEA. Our previous genetic and molecular analyses have shown that rg encodes an A kinase anchor protein (DAKAP 550), which interacts with components of the epidermal growth factor receptor or EGFR and Notch-mediated signaling pathways, facilitating cross talk between these and other pathways (Shamloula et al., 2002). We now present functional data from studies on the larval neuromuscular junction that reveal abnormal synaptic architecture and physiology. In addition, adult rg loss-of-function mutants exhibit defective social interactions, impaired habituation, aberrant locomotion, and hyperactivity. These results demonstrate that Drosophila NBEA (rg) mutants exhibit phenotypic characteristics reminiscent of human ASD and thus could serve as a genetic model for studying ASDs.

Conditions Affecting Social Space in Drosophila melanogaster

The social space assay described here can be used to quantify social interactions of Drosophila melanogaster - or other small insects - in a straightforward manner. As we previously demonstrated (1), in a two-dimensional chamber, we first force the flies to form a tight group, subsequently allowing them to take their preferred distance from each other. After the flies have settled, we measure the distance to the closest neighbor (or social space), processing a static picture with free online software (ImageJ). The analysis of the distance to the closest neighbor allows researchers to determine the effects of genetic and environmental factors on social interaction, while controlling for potential confounding factors. Diverse factors such as climbing ability, time of day, sex, and number of flies, can modify social spacing of flies. We thus propose a series of experimental controls to mitigate these confounding effects. This assay can be used for at least two purposes. First, researchers can determine how their favorite environmental shift (such as isolation, temperature, stress or toxins) will impact social spacing (1,2). Second, researchers can dissect the genetic and neural underpinnings of this basic form of social behavior (1,3). Specifically, we used it as a diagnostic tool to study the role of orthologous genes thought to be involved in social behavior in other organisms, such as candidate genes for autism in humans (4).

Straightforward Assay for Quantification of Social Avoidance in Drosophila melanogaster

Drosophila melanogaster is an emerging model to study different aspects of social interactions. For example, flies avoid areas previously occupied by stressed conspecifics due to an odorant released during stress known as the Drosophila stress odorant (dSO). Through the use of the T-maze apparatus, one can quantify the avoidance of the dSO by responder flies in a very affordable and robust assay. Conditions necessary to obtain a strong performance are presented here. A stressful experience is necessary for the flies to emit dSO, as well as enough emitter flies to cause a robust avoidance response to the presence of dSO. Genetic background, but not their group size, strongly altered the avoidance of the dSO by the responder flies. Canton-S and Elwood display a higher performance in avoiding the dSO than Oregon and Samarkand strains. This behavioral assay will allow identification of mechanisms underlying this social behavior, and the assessment of the influence of genes and environmental conditions on both emission and avoidance of the dSO. Such an assay can be included in batteries of simple diagnostic tests used to identify social deficiencies of mutants or environmental conditions of interest.