olfactory habituation assay to gain genetic and behavioral insights into autism spectrum disorder using drosophila models

&lt;i&gt;Drosophila&lt;/i&gt; Models for Genetic and Behavioral Traits of Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) encompasses a heterogeneous group of neurological disorders. It includes a range of complex neuro-developmental disorders characterized by multi-contextual and persistent deficits in social communication and social interaction and the presence of restricted, repetitive behavioral and activity patterns and interests1. According to World Health Organization (WHO), 1 in 100 children is diagnosed with ASD worldwide with a male-to-female ratio of 4.22. The disease becomes evident in the second or third year of life. ASD children show a lack of interest in social-emotional reciprocity, non-verbal communication, and relationship skills. They exhibit repetitive behaviors like stereotyped motor movement, inflexible and ritualized routine following, and intense focus on restricted interests. ASD children show a high degree of response towards touch, smell, sound, and taste whereas pain and temperature response is comparatively low1. The penetrance of this disorder is also different among different patients suffering from ASD and hence, the variability increases.
Current clinical diagnosis of ASD is based on behavioral assessment of the individuals as there is no confirmatory biomarker-based or common genetic test that covers all forms of ASD3. Deciphering the genetic and neurophysiological bases would be helpful in targeting treatment strategies. In the last decade, a large body of research has resulted in the identification of hundreds of genes that are either deleted or mutated or whose expression levels are altered in ASD patients. Ongoing research emphasizes the validation of the contribution of these candidate genes using model organisms like the mouse or fruit-fly, in which, these genes are knocked out or knocked down followed by tests for ASD-like behavioral deficits and elucidation of underlying genetic and molecular pathways causing the anomalies. A mouse model recapitulating Copy Number Variations (CNVs) in the human chromosomal loci 16p11.2 shows some of the ASD behavioral defects4,5,6. Prenatal exposure to a teratogenic drug valproic acid (VPA) is another mouse model depicting traits resembling human ASD7,8. In addition, there exists a range of mouse models that exhibit genetic syndrome-associated autism, for example, single-gene syndromic models caused by mutations in Fmr1, Pten, Mecp2, Cacna1c, and single-gene non-syndromic models caused by mutations in genes like Cntnap2, Shank, Neurexin, or Neuroligin genes5.
Fruit-fly (Drosophila melanogaster) is another prominent model organism for studying the cellular, molecular, and genetic bases of a plethora of human disorders9, including ASD. Drosophila and humans share highly conserved biological processes at the molecular, cellular, and synaptic levels. Fruit-flies have been used successfully in ASD studies10,11,12 to characterize genes linked to ASDs and decipher their exact role in synaptogenesis, synaptic function and plasticity, neural circuit assembly, and maturation; fly homologs of ASD-associated genes were found to have roles in the regulation of social and/or repetitive behavior11,13,14,15,16,17,18,19,20,21. The fruit-fly has also worked as a model for the screening of ASD genes and their variants15,22,23. The biggest challenge in ASD research in flies is that, unlike other disease models, there is no single ASD fly model. To understand the impact of mutations or knocking down of a specific ASD gene, a researcher needs to validate whether the behavioral phenotypes sufficiently mimic the symptoms of ASD patients and then, proceed towards understanding the molecular or physiological underpinnings of the phenotypes.
Hence, the detection of ASD-like phenotypes is vital to ASD research in the fly model. A handful of behavioral techniques have emerged over the years that enable us to detect abnormalities like deficits in social behavior/interaction, communication, repetitive behaviors, and responsiveness to stimuli. In addition, several modifications and upgrades of these behavioral techniques have been made in different labs to suit specific requirements such as upscaling, automation of assays, readouts, quantification, and comparison methods. In this video article, the most basic versions of five behavioral paradigms are demonstrated, which, in combination, can be used to detect ASD-like behavioral outcomes in the easiest way.
Aggression is an evolutionarily conserved innate behavior affecting survival and reproduction24. Aggressive behavior towards conspecifics is influenced by &#39;motivation for socialization&#39;25,26 as well as &#39;communication&#39;27, both being compromised in ASD-affected individuals. Aggressive behavior is well described in Drosophila and its quantifiability through the robust aggression assay28,29,30 and a well-understood genetic and neurobiological basis31 makes it a suitable behavioral paradigm32 for assessing the ASD phenotype in a fly model. Aggression is affected by social isolation away from a social environment, which leads to enhanced aggression; the same has been observed when male flies are housed in isolation for a few days33,34. Another behavioral assay that quantifies sociability in flies is the Social Space Assay35, which measures distances between nearest neighbors and interfly distances in a small group of flies, making it perfectly suited for testing the roles of ASD gene orthologs in fly12,21,36,37 as well as environmentally induced ASD fly models38,39.
The Drosophila courtship assay is another behavioral paradigm frequently used to assay for alteration in social and communication skills upon circuit or genetic manipulation, including Autism related genes18,19,21,40. Repetitive patterns of behavior are prevalent in ASD patients, which is recapitulated in flies by grooming behavior-a series of distinct, stereotyped actions performed for cleaning and other purpose. It has been successfully used to assay for the impact of ASD gene mutations in flies21,41 as well as exposure to chemicals38,39. Multiple advancements and automation in the assay have been described before16,41,42,43; here, we are demonstrating the most basic assay pattern, which is easy to adopt and quantify.
ASD is known to impact the ability for habituation, learning, and memory in some patients44,45,46,47,48,49,50, ASD model organisms51,52 and also causes deficits in different olfactory behaviors50. Drosophila light-off jump habituation has been used previously to screen for ASD genes23. Habituation can be assayed by a simple method of olfactory habituation assay53,54,55. We describe the method to induce olfactory habituation and assay the outcome using a classic Y-maze-based binary odor-choice assay56 that can be used to detect defects in habituation in ASD gene mutant or gene knockdown condition. To assess whether the impact of a mutation (or gene knock-down) or a pharmacological treatment on the behavior of a fly amounts to an ASD-like phenotype, one can use a combination of these 5 assays described here.

Author Spotlight: Exploring Autism Spectrum Disorder Symptoms in Fruit Flies &amp;#8212; Genetic Models and Behavioral Tests

Paradigms for Behavioral Assessment in Drosophila Model of Autism Spectrum Disorder

Autism spectrum disorder affects children, leading to impaired communication, social behavior, and enhanced repetitive behavior. Drosophila is an increasingly popular model for autism research to decipher underlying molecular pathways. We describe a set of standard techniques for behavioral characterization of fly autism models.For decoding the molecular underpinnings of autism spectrum disorder in flies, its behavioral manifestations must be precisely established. Quantifying human behavioral traits of autism in Drosophila melanogaster is quite a challenging task. There is no single behavioral paradigm in flies that addresses all the behavioral anomalies of this disorder.We have described a set of five well-established behavioral paradigms in Drosophila, namely, aggression assay, social space assay, coat shape, grooming, and habituation assay. All of these can be used in ASD fly models to characterize and quantify the level of impairments in communicative behavior, repetitive behavior, and social behavior. We described these five techniques in their simplest form so that every lab with minimal fly research facility can adopt them with ease and perform experiments on fly model of autism spectrum disorder, and contribute to the advancement of our understanding of this disease.

Olfactory Habituation Assay to Gain Genetic and Behavioral Insights into Autism Spectrum Disorder Using Drosophila Models

To begin, obtain the flies prepared for habituation assay. Place one milliliter of the preferred odorant diluted with paraffin liquid light in a 1.5 milliliter microfuge tube. Vortex the tube for 10 minutes and cover it with evenly perforated plastic wrap.Using a wire, suspend the odorant tubes in separate media bottles containing flies. Cover the bottle well with cotton and wrap it with craft paper to prevent a fusion of the odor and vapor. Label the control and odor-containing bottles as naive and odor-exposed respectively.Maintain these induction bottles for three days in an incubator. For the Y-maze assay, attach the Y-maze to the adapter, fix the bottom of the Y-maze to the entry vial, and then attach to climbing chambers to the two arms of the Y-maze. Using odor-free silicone tubes, connect the tapering end of each climbing chamber with the reagent bottle containing the odorant.With the vacuum pump, drive the odorant from the gas bottles to the two arms of the Y and let it saturate for 15 minutes. Gently introduce the star flies of each vial into the entry vial of the Y-maze setup. After brief acclimatization, connect the entry vial with the Y-maze adapter to begin the test.Let the flies climb the Y-maze arms and get trapped in the two collection chambers for over one minute. Upon completion, tap back the flies to the bottom of the entry vial and switch the position of the arms of the Y-maze to avoid side bias. Record the number of flies climbing each of the two arms of Y-maze within the time duration.The row knockdown flies did not get habituated after a three day odorant exposure as compared to the wild-type flies.

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Research

JoVE Journal

Neuroscience

67 Views. To begin, obtain the flies prepared for habituation assay. Place one milliliter of the preferred odorant diluted with paraffin liquid light in a 1.5 milliliter microfuge tube. Vortex the tube for 10 minutes and cover it with evenly perforated plastic wrap.Using a wire, suspend the odorant tubes in separate media bottles containing flies. Cover the bottle well with cotton and wrap it with craft paper to prevent a fusion of the odor and vapor. Label the control and odor-containing bottle...

Video: Olfactory Habituation Assay to Gain Genetic and Behavioral Insights into Autism Spectrum Disorder Using Drosophila  Models

Autism Spectrum Disorder (ASD) encompasses a heterogeneous group of neurodevelopmental disorders with common behavioral symptoms including deficits in social interaction and ability for communication, enhanced restricted or repetitive behaviors, and also, in some cases, learning disability and motor deficit. Drosophila has served as an unparalleled model organism for modeling a great number of human diseases. As many genes have been implicated in ASD, fruit flies have emerged as a powerful and efficient way to test the genes putatively involved with the disorder. As hundreds of genes, with varied functional roles, are implicated in ASD, a single genetic fly model of ASD is unfeasible; instead, individual genetic mutants, gene knockdowns, or overexpression-based studies of the fly homologs of ASD-associated genes are the common means for gaining insight regarding molecular pathways underlying these gene products. A host of behavioral techniques are available in Drosophila which provide easy readout of deficits in specific behavioral components. Social space assay and aggression and courtship assays in flies have been shown to be useful in assessing defects in social interaction or communication. Grooming behavior in flies is an excellent readout of repetitive behavior. Habituation assay is used in flies to estimate the ability for habituation learning, which is found to be affected in some ASD patients. A combination of these behavioral paradigms can be utilized to make a thorough assessment of the human ASD-like disease state in flies. Using Fmr1 mutant flies, recapitulating Fragile-X syndrome in humans, and POGZ-homolog row knockdown in fly neurons, we have shown quantifiable deficits in social spacing, aggression, courtship behavior, grooming behavior, and habituation. These behavioral paradigms are demonstrated here in their simplest and straightforward forms with an assumption that it would facilitate their widespread use for research on ASD and other neurodevelopmental disorders in fly models.

Autism Spectrum Disorder (ASD) is associated with impaired social and communicative behavior and the emergence of repetitive behavior. For studying the interrelation between ASD genes and behavioral deficits in the Drosophila model, five behavioral paradigms are described in this paper for assaying social spacing, aggression, courtship, grooming, and habituation behavior.

Autism Spectrum Disorder (ASD) encompasses a heterogeneous group of neurodevelopmental disorders with common behavioral symptoms including deficits in ...

Aggression Assay in Drosophila to Analyze Autism Spectrum Disorder &#40;ASD&#41;&#45;Related Communication and Social Behavior Deficit

To begin, take a standard 24-well plate and fill half of each well with regular fly food. Let the food dry overnight. Make a small, 2.5-millimeter hole on a transparent plastic or acrylic sheet and place it over a well plate.Using a stereo microscope, separate newly enclosed flies of the desired genotype based on their sex. Insert half the male flies individually into single housing tubes. Keep the other half of the male flies in a group of 10 with the female flies in a regular group housing vial, creating a social condition.Store all vials at 25 degrees Celsius for five days. Mouth aspirate two male flies from either the single or group housing chambers to the aggression arena plate through the hole in the lid. Move the hole away immediately to ensure that the flies cannot escape.After one to two minutes of acclimatization, start a timer for 20 minutes. Make sure to video record the flies. Play the video on a computer and count the total number of aggressive bouts for each fly.The number of aggressive bouts in 20 minutes was significantly reduced in the case of mutant males than in the control males.

Social Space Assay to Explore Social Behavior Defects in the Drosophila Model of Autism Spectrum Disorder

To begin, separate the male flies from a mixed population of flies on ice and put them in a collection vial. To prepare the arena, place two triangular acrylic spacers flat on top of a rectangular glass pane, such that the right angles of the acrylic spacers are aligned with the corners of the glass pane. Then place two rectangular acrylic spacers flat on the glass pane aligned with the bases of the two triangular spacers.Confirm that the four acrylic spacers surround a triangular arena on the rectangular glass pane that is not covered by spacers. Position a sticker of a ruler on one of the triangular spacers, ensuring that it is visible from the top. Now place a second rectangular glass pane on top of the acrylic spacers to align it with the glass pane at the bottom.Using four small binder clips, secure the panes and spacers. For the assay, remove the bottom right binder clip and slightly shift the rectangular spacer outwards to create a gap. To transfer flies from the collection vial into the social space arena, gently aspirate them through the created space.Immediately slide the rectangular spacer and secure the binder clip back in its position. Holding the chamber upright, gently pound three times onto a soft pad to let all the flies settle at the base. Clamp the chamber in the upright position and start the timer.Take a clear photo of the arena after 20 minutes. Analyze with ImageJ to list the inter-fly nearest neighbor distances. The mutant flies show significantly higher nearest neighbor distances than the control counterparts, indicating a preference for greater distancing from other flies.

Courtship and Grooming Behavior Assay to Study Autism Spectrum Disorder in Drosophila

To begin, assemble all four pieces of the courtship chamber together. Using the aspirator, gently transfer a five-day isolated test male fly from the single housing tube to the courtship chamber containing the single premated female. Rotate the lid quickly to close the chamber.Record the behavior of the flies for 15 minutes to calculate the courtship index and total number of copulation attempts. After setting up the assay arena, transfer a single housed male fly into the arena with an aspirator. Immediately slide away the hole in the lid to prevent the fly from escaping.Place the grooming arena on a diffused LED panel and let the fly acclimatize for one minute. Video record the fly for 10 minutes. Analyze the videos and calculate the grooming index, grooming latency, grooming bout number, and mean grooming bout duration.Mutant flies showed a significantly lower courtship index, as well as a reduced number of attempts to copulate. Latency to first grooming was significantly decreased in the mutant flies, whereas the mean grooming bout duration and grooming index were significantly increased.