Herman Dierick - US grants

The extensive interactivity among genes that is now being revealed suggests that there is considerable flexibility in the genome's capacity for responding effectively to diverse conditions. In a model gene network, centering on a temperature-sensitive mutation in the Syntaxin1A gene affecting synaptic transmission in Drosophila, a high degree of flexibility has been observed and the interactions underlying the various states of the network will now be analyzed. The phenotypic space of the network's functionality will be explored and the patterns of gene expression associated with various different genotypes and system outputs assayed. Functional clustering analysis, a measure based on the mutual information in the system, will be applied to these data to construct testable models and predictions of gene interaction. The outcome of this research offers possibilities for new kinds of network strategies and architectures.
The overall goal of the work is to test the idea that gene networks operate by the same fundamental principles as neuronal networks, of which degeneracy is one of the key characteristics. The gene network surrounding Syntaxin will be analyzed by synthesizing various allele combinations, dividing them into groups with quantitatively similar phenotypes, and comparing the gene expression patterns within and between groups. A particular focus will be those genotypes that produce similar scores, as a window into the various network configurations that are capable of producing similar outputs (i.e., system degeneracy). From this analysis, models will be generated and predictions made of which (and how many) gene combinations stabilize the phenotype, and these will be tested by constructing and analyzing further mutant combinations.

Aim 1: Perform bi-directional selection on a population of flies in which all of these alleles (Syx1A3-69and EPs) are randomly segregating to derive strains with extreme sensitivity or resistance to paralysis.

Aim 2: Perform array analyses on a subset of phenotypic groups of genotypes from EP and Df analyses, as well as on the selected and control strains.

Aim 3: Apply functional clustering based on phenotype and array results, and make predictions on phenotypes of novel combinations. Test novel combinations phenotypically, and molecularly.

Gene networks are likely to share common organizational and operational principles with neuronal networks, and with biological networks in general, despite their very different modes and kinetics of internal communication and connection. This proposal addresses the issue directly, by taking a representative gene network and analyzing it with tools developed and validated for neuronal networks.
The experiments outlined above constitute a new approach to the question of whether there are fundamental underlying principles of biological network operation which, if discerned, would have wide-ranging implications for the design and implementation of artifical networks constructed for applications as diverse as computing, engineered adaptive devices, and communications.

Aggressive behavior is pervasive in the animal kingdom. It is the result of interactions between stimuli from the environment and internal activity of the brain. Although aggression is influenced by the environment, genetic differences between animals also play an important role in this behavior. In this project, aggression is studied in the laboratory fruit fly, Drosophila melanogaster. Male fruit flies display obvious aggression responses in the presence of food territories and females. Even in the absence of these triggers, aggression can be observed albeit at lower frequency. The aggression responses are measured with simple and reproducible assays. Moreover, the fruit fly offers the advantage of a large number of genetic and neurobiological tools to analyze this behavior. Using these tools, the behavior will be dissected to better understand the mechanisms. Preliminary studies suggest that the basic molecular machinery regulating the drive to display aggression appears to be very similar between flies and mice. In addition, these studies also show that the neurons that regulate the behavior in the fruit fly are also surprisingly similar to neurons in mice that are known to regulate mammalian aggression. The function of the conserved machinery in these functionally similar neurons will be further studied in this series of experiments. These studies may identify a basic mechanism involved in the regulation of aggression in all animals.
These studies will drive the field of study of aggression in a new direction: from a main focus on hormonal control and modulation to transcriptional control in specific neuronal targets to integrate environmental responses that result in optimal adaptive behavior. The laboratory uses state of the art technology and resources for training the next generation of scientists. The lab actively participates in the training of minority students through the SMART program and the Houston Community College Science Intern Program.

? DESCRIPTION (provided by applicant): Aggressive behavior is a complex social behavior that is influenced by genetic and non-genetic factors. The cost of violence in the US alone is estimated to be $70 billion annually. It is important to understand the mechanisms of aggression to help alleviate this socio-economic burden. In addition, a variety of diseases are characterized by abnormal aggression and little is known about the causes of these behavioral abnormalities, which has hampered the development of successful therapies. We propose to study the transcriptional regulation of aggression in specific neuronal circuits controlling aggression using the model organism Drosophila melanogaster. We will focus on a mechanistic dissection of a conserved transcription factor, Tailless (Tll) (known as Nr2e1 in mammals) with shared binding sites, binding partners and targets in flies and mammals. We recently showed that Drosophila Tll and its conserved co- repressor, Atrophin (Atro), regulate aggression by affecting the activity of a group of neurosecretory neurons in the adult fly brain. We show that Tll controls the release of neuropeptides from these neurosecretory cells and that this is required for increased aggression. These findings further support evidence in the literature that suggest that these neurons have structural, developmental and functional similarities to the hypothalamus, a region critically involved in aggression regulation in mammals. Our studies therefore suggest the existence of an evolutionarily ancient transcriptionally controlled set of neurosecretory cells governing aggressive behavior. In this proposal we will use the large neurobiological and genetic toolkit available in Drosophila to analyze the mechanism of the transcriptional regulation of aggression in flies. We will dissect the neuropeptide-based mechanism that is necessary and sufficient for the regulation of aggression in the PI and we will examine the connection with Tll. To do so, we have developed a new transposon-based tool to study gene-specific expression, allowing functional manipulation of the cells expressing the gene of interest. This tool will be useful for many researchers in the community as it can be applied to many genes in the genome. Finally, we will examine two binding partners of Atro, the co-repressor of Tll that also affects aggression through the neurosecretory cells of the PI and that physically interacts with Tll. One of the binding partners of Atro is encoded by the ortholog of a disease gene mutated in a human syndrome that is characterized by abnormal aggressive behavior. The mechanism of the behavioral abnormalities in these patients is completely unknown as is the case for most of the diseases associated with excessive aggression. Our proposed experiments will help elucidate the role of this gene in aggression. Together the experiments in this proposal will begin to unravel the mechanisms that underlie transcriptional control of aggression in flies. Given the conservation of this molecular pathway, our proposal will open a new direction in the field that will shed light on this complex behavior.

DESCRIPTION (provided by applicant): Complex behaviors such as aggression are the result of interactions between external stimuli from the environment and the internal activity of the brain. Some individuals are very aggressive while others are very passive. Even though this is in large measure context dependent, there is a clear genetic component that is involved in aggression in all known species. Because aggression occurs widely in the animal kingdom it is possible that the genetic mechanisms that cause this behavior are similar in all species and derive from their common evolutionary ancestry. We study aggression in Drosophila melanogaster, and have developed simple test systems to measure the amount of fighting behavior between male flies. We also use an automated analysis method as an independent measure of aggression. Recently, we have identified a transcriptional control module that appears to be remarkably conserved between flies and mammals. We identified two transcriptional repressors that regulate the activity of neurosecretory cells in the adult fly brai affecting the release of neuropeptides. In addition to this transcriptional regulation mechanism, neuromodulatory control of aggression is another critical mechanism in the control of aggressive behavior. This proposal focuses on the identification of a minimal circuit that is crucial for the modulation of aggressive behavior. We have previously shown that aggression in flies is strongly affected by serotonin (5-HT) modulation. Here, we propose to identify the serotonin receptor that is necessary and sufficient for serotonergic modulation of aggression. We will also identify the critical set of receptor expressing neurons that receive the serotonin signals and those that produce it. This will establish the minimal circuit that is necessary and sufficient for serotonergic modulation of aggression. This research will help understand how a complex set of neuromodulatory neurons that affect a wide range of physiological and behavioral responses is capable of specificity of these different responses through specific subcircuits with specific receptors.

The goal of the proposal is to elucidate the neural computations carried out by the visual system to identify an impending threat and their use for the generation of collision avoidance behaviors. The proposal will develop advanced genetic, behavioral and imaging techniques to address these questions. The experimental data will be summarized in a biophysical model of the neural circuits generating collision avoidance behaviors that will be validated using the experimental data acquired during the project. The project will advance our understanding of how the visual system goes about reliably identifying a threat in the natural visual environment without reacting to irrelevant visual stimuli. The knowledge gained from the project is expected to allow the future design of efficient, neurally-inspired collision avoidance systems.

The proposed experiments will be carried out in the fruit fly Drosophila, a model system in which sophisticated genetics tools are available, including genetically encoded Ca2+ indicators and modifiers of neural activity that can be expressed in specific neural subpopulations. These tools, paired with the recent anatomical description of visual pathways at the electron microscopic level, offer the possibility of investigating how networks of neurons process information leading to visually guided escape behaviors at an unprecedented level of detail. In particular, these tools will allow (1) to carry out behavioral experiments where specific populations of neurons belonging to the visually-guided escape pathway are silenced; (2) to perform imaging experiments allowing to study the activation of the neurons belonging to the visually-guided escape pathway at all successive stages of the visual system and determine how/when the specificity for looming stimuli arises; (3) to apply localized stimuli and advanced microstimulation techniques allowing to isolate the contribution of individual photoreceptors to the processing of visual information related to looming stimuli in single neurons; (4) to develop genetic tools allowing to silence populations of neurons by using novel anion channel rhodopsins and allowing to sparsely label neurons of the pathway at two successive stages, either with an indicator of neuronal activity or with an optogenetic activator; (5) to test the functional connectivity at successive stages of the pathway using these tools in conjunction with three dimensional random access imaging; and (6) to model the neural computations carried out along the visually guided escape pathway.

Locusts are grasshoppers that can form enormous migrating swarms, once vividly recorded in ancient texts, but still occurring to this day and affecting the livelihood of one in ten people on Earth. Currently, multiple continents are experiencing locust plagues that threaten food security both locally and on a larger, potentially global, scale. What makes locusts particularly devastating is their ability to change their behavior depending on population density ? this is known as locust phase polyphenism. At low density, they are solitary and harmless grasshoppers, but at high density, they become gregarious and voracious pests that migrate. This plasticity, or variation, in behavior, appearance, and physiology is striking and how population density facilitates this change is still not fully understood. Studying the mechanism of this transformation holds the key to developing effective methods of control for this organism, ensuring food safety, and understanding how social/population pressures can fuel radical change in these animals. This undertaking will require comprehensive scientific integration across different biological disciplines to be accomplished. To address this challenge, a group of researchers has formed a cross-institutional, cross-disciplinary Biological Integration Institute ? the Behavioral Plasticity Research Institute (BPRI). Using cutting-edge technologies in research projects spanning from molecules to landscapes, the BPRI will greatly enhance our understanding of locust phase polyphenism and plasticity in other organisms. With a commitment to improving diversity, inclusion and equity, the institute will train the next generation of integrative biologists who can efficiently navigate across different disciplines. The institute will communicate groundbreaking research to the general public and the scientific community through video documentaries, symposia and workshops. The BPRI will partner with the Global Locust Initiative to translate the scientific advances to management for improving global food system sustainability.


Phenotypic plasticity ? the ability of a single genotype to produce different phenotypes in response to different environmental conditions ? is ubiquitous in nature and occurs across all scales of biological organization. To understand its mechanisms, maintenance, and evolution, complete biological integration is needed. Locust phase polyphenism represents one of the most striking examples of phenotypic plasticity. It also provides a powerful comparative system for understanding how gene expression patterns and epigenetic regulation are linked to shifts in behavior, physiology, and ecology that result in outbreaks, collective movement, and mass migration. The Behavioral Plasticity Research Institute (BPRI) will comprehensively dissect this phenomenon and use it as a model system to transform the study of phenotypic plasticity. Specifically, the BPRI will carry out ten integrative research activities, using three locust and three non-swarming grasshopper species with varying degrees of plasticity in the genus Schistocerca. The BPRI research will provide in-depth understanding of proximate mechanisms of locust phase polyphenism by generating high-quality reference genomes, complemented by tissue-specific and time-resolved transcriptomes and epigenomes, as well as CRISPR/Cas9 and reverse genetics tools to understand functional genetics. These mechanistic approaches will be integrated with organismal biology and ecology to investigate phase-associated nutritional physiology and ecological factors contributing to swarming under laboratory and field conditions. All research activities will be performed across species in a phylogeny-based comparative framework. The feedback among these activities will create synergies and lay the groundwork for the integrative study of phenotypic plasticity across model organisms from genomes to ecology and sustainability.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.