Photo: Model organisms we study
Left to right:The fruit fly, Drosophila melanogaster; the yellow fever and Dengue vector mosquito, Aedes aegypti; normal human subjects. Stock photo credits: Fotolia.com (©Studiotouch ©EW CHEE GUAN ©sculpies)

The overall goal of work in our laboratory is to understand how complex behaviors are modulated by external chemosensory cues and internal physiological states. The lab takes a multi-disciplinary approach spanning cell biology, genetics, neurobiology and behavior. Our early focus has been to study how the brain interprets olfactory signals in the environment that signal food, danger, or potential mating partners. We have been studying these problems in three model organisms: the fly, the mosquito and the human. The majority of the early work in the laboratory was carried out in the genetically tractable fruit fly, Drosophila melanogaster, which displays a rich repertoire of chemosensory behaviors despite having a nervous system with only 100,000 neurons. In this animal, we have studied the functional neuroanatomy of the olfactory system, how this system perceives sex pheromones, and the structure and function of the insect odorant receptors.

We have recently expanded our research focus in three major directions. First, we are establishing a mosquito genetics research program to understand host-seeking and blood-feeding behavior in the mosquito. Second, we are carrying out large-scale human subjects research to combine olfactory psychophysics with genetic analysis to understand the mechanisms of olfactory perception in humans. Third, we are getting increasingly interested in the links between olfaction and feeding behavior and hope to use Drosophila as a powerful model to understand how smell intersects with hunger and satiety in all animals.

The long-term goal of all of our work is to understand how behaviors emerge from the integration of sensory input with internal physiological states.

Research in our lab is supported by the Howard Hughes Medical Institute, the National Institutes of Health/National Institute of Deafness and Other Communication Disorders (current grants: RO1 DC006711, RO1 DC008600; past grant: RO1 DC005036), the Klarman Family Foundation Grants Program in Eating Disorders Research, the Irma T. Hirschl Trust, and the Grand Challenges in Global Health Initiative of the Bill and Melinda Gates Foundation, administered by the Foundation for the National Institutes of Health. We are grateful for past support from the National Science Foundation, the John Merck Foundation, the Arnold and Mabel Beckman Foundation, and the McKnight Endowment Trust for Neuroscience.

Current Projects

Fly courtship behavior A male fly (right) courting a female fly (left) while both walk across a banana slice.

Pheromones, courtship, and social and sexual behavior in the fly
Michael Crickmore, Ph.D.
Jennifer Bussell
Steve Conway

How complicated behaviors arise from and are regulated by the brain is perhaps the greatest mystery in biology. Sexual behavior in the fly provides a reductionist and genetically malleable system for addressing this mystery. Drosophila melanogaster exhibit a particularly well-studied sexually dimorphic set of innate behaviors in their precopulatory courtship. In the classical view, male Drosophila initiate courtship and perform stereotyped behaviors in order to woo the female. The female, for her part, may respond by being receptive to copulation or avoiding it. We are interested in understanding how flies use courtship to make the decision whether, and with whom, to mate. The decision to mate is based first of all upon the drive to reproduce, and both the fly's internal state and sensory information from the environment influence the choice. During courtship, flies gather information about potential mates via visual, auditory, tactile, and chemical cues. We want to understand how these cues are interpreted by the fly to decide whether or not to mate with a given individual. Some of the most important chemical cues used by insects are sex pheromones, and previous work in our laboratory identified four candidate pheromone receptors in Drosophila, suggesting that Drosophila also may use volatile sex pheromones to communicate prior to mating. We will take advantage of the genetic tools available in this system to approach the mechanisms of pheromone perception in Drosophila. Finally, previous analyses of courtship have largely focused on the behavior of the male, but given the equal importance of mating to females, we are working to understand the female's role in the decision to mate.

click to enlarge

Identification of novel genes and circuits in an animal model of binge eating disorder
Gabriel Gasque, Ph.D.
Steve Conway

The etiology of compulsive feeding behaviors including bulimia nervosa and binge eating disorder in humans is poorly understood. We propose that studying these important clinical conditions in a simpler genetic model system, the larva of the fruit fly Drosophila melanogaster, may shed new light on this important health problem. Fruit flies go through four distinct life stages: embryo, larva, pupa, and adult. While adult flies regulate their feeding according to hunger status and the circadian clock just like normal humans, the larva resembles a binge eater because it feeds continuously for nearly 72 hrs, eating 3-5 times its own weight in food. About 24 hrs before puparation, the larva abruptly leaves the food medium and stops eating. This highly stereotyped behavior provides an attractive experimental model to explore the neuronal mechanisms that drive and sustain continuous (compulsive) feeding. We hypothesize that continuous feeding in the Drosophila larva is a behavior accessible to genetic and pharmacological modulation. We are carrying out microarray analysis to identify candidate genes subject to regulation during continuous feeding. Using a genome-wide RNA interference (RNAi) screen, we hope to identify genes that modulate food intake. We will complement the RNAi screen with a small molecule screen that will look for compounds that reduce food intake. Finally, we will study the neuronal circuits modulating continuous feeding. Our long-term goal is to identify genes and neuronal circuits mediating the continuous feeding behavior of larvae and to prove that this compulsive-like behavior can be decreased by specific pharmacological interventions. We hope to illuminate common principles underlying the regulation of feeding behavior that will be applicable to parallel processes occurring in human patients suffering from compulsive eating disorders.

Funded by a grant from the Klarman Family Foundation Grants Program in Eating Disorders Research.

Molecular biology of the insect odorant receptors
Takao Nakagawa, Ph.D.
Laura Seeholzer

Insects have exquisitely sensitive olfactory systems that are tuned to food odors and pheromonal cues emitted by members of the same species. We have been studying the molecular mechanisms by which insect olfactory neurons respond to and discriminate among the numerous possible odors in the environment. Several years ago, we and others identified a divergent family of seven transmembrane domain receptors now known to be the insect odorant receptors (ORs). One member of the odorant receptor gene family, Or83b, has the unique property that it is expressed in nearly all olfactory neurons. Therefore, each olfactory neuron in the fly is likely to express a conventional odorant receptor along with the co-receptor Or83b. Our recent work has shown that the insect odorant receptor is a heteromeric complex of the OR83b co-receptor with a conventional ligand binding odorant receptor. OR83b is necessary and sufficient to target this OR/OR83b complex to the ciliated dendrite of the olfactory sensory neuron. Together with our collaborator Dr. Kazushige Touhara and colleagues at the University of Tokyo, we investigated whether OR83b has additional signaling functions beyond its role in ciliary trafficking. Our recent work provides strong evidence that the OR/OR83b complex forms an odor-gated non-selective cation channel that does not depend upon G protein signaling. We are carrying out a large-scale in vivo structure-function analysis of OR83b and the conventional odorant receptors to further probe the biology of these unusual membrane receptors. The goal is to map those domains that are necessary for the heteromeric association of the OR/OR83b complex, domains necessary for trafficking, and residues that are necessary for odor signal transduction. We are particularly interested in discovering which residues may contribute to forming the ion-conducting pore. Going beyond conventional genetics, are using chemical biology to probe for small molecules that interfere with heterodimerization, trafficking, or signaling of OR/OR83b complexes. Some of these compounds may be useful elements in a chemical strategy to block olfactory host-seeking behaviors in mosquitoes and other pest insects. These compounds may act as insect repellents that could be useful to control insect vectors that transmit human infectious diseases.

Genetic basis of specific anosmias in humans

Andreas Keller, Ph.D.
Peggy Hempstead, R.N.

As part of our overall mission to understand the genetic and neuronal basis of how odors guide behaviors, we are conducting psychophysical studies with human subjects to find correlations between genetic variability in odorant receptor genes and variability in cognitive and physiological responses to odors. In collaboration with Hiro Matsunami's group at Duke University we have shown that variability in one odorant receptor gene, OR7D4, influences the perception of odorous steroids. Currently we are extending our studies to include more odors, more odorant receptor genes, and an array of physiological and psychological responses to odors. Our most recent study investigates the genetic basis of changes in salivary cortisol, mood, and skin conductance (a measure of general arousal) induced by an odorous steroid.

To learn more about The Rockefeller University Smell Study or to consider enrolling as a volunteer, email us or consult our web page. The CAFE assay A male fly feeding from a capillary containing a dyed sugar solution. Olfactory adaptation to feeding state in Drosophila melanogaster Nilay Yapici, Ph.D. Isabel Gutierrez The ability of animals to adapt their feeding behavior in response to hunger and satiety cues is important for survival and in the natural world where food resources fluctuate. Prior studies in vertebrates and in worms suggest that this adaptation may involve modulation of the chemosensory system in response to food intake, though little is known about the mechanism for this proposed sensory adaptation. We have been examining the behavioral response of adult Drosophila melanogaster flies to odor cues and food in starved and in fed states. Flies that have been starved for 24 or 48 hours show significantly increased olfactory behavior preference for a food odor (3-methylthio-1-propanol) when tested in a two-choice odor preference assay. There is a corresponding increase in food intake in such animals. Using whole genome microarrays, we have identified a set of genes in Drosophila that are regulated by starvation and that are candidates for molecular regulators of this behavioral phenotype. Forty genes show at least a ten-fold increase or decrease in fly heads after 24 hours of starvation. These may represent transcripts that function to modulate behavior in response to feeding state. In antennae, forty genes are likewise either up or down regulated in response to 24 hours of starvation, suggesting that feeding state modulates gene expression in peripheral olfactory organs. Our results demonstrate that insect olfactory preference can depend on feeding state, and we are investigating candidates genes that may regulate this behavior. Mosquito blood-feeding behavior A female Aedes aegypti mosquito prepares to take a blood meal from a human. Regulation of blood-feeding and host-seeking behavior in the mosquito Aedes aegypti Jeff Liesch Conor McMeniman, Ph.D. Jermaine Watson, M.S. Chloe Goldman Laura Seeholzer Olfactory cues guide mosquitoes toward humans, from which the mosquitoes derive the blood they need to complete ovarian development. We are carrying out two conceptually related projects in mosquitoes. In the yellow fever and dengue vector mosquito, Aedes aegypti, host-seeking is suppressed or inhibited for about 72 hours after the mosquito takes a blood meal. The molecular basis for how host-seeking behavior is regulated is unknown, but may be explained by a humoral control mechanism in which the sensitivity of the olfactory system is altered following blood-feeding. In this project, we are examining the hypothesis that regulation of specific olfactory and neurohumoral genes modifies the host-seeking behavior of female Aedes aegypti after blood-feeding. Genetic analysis of skin odor perception in Aedes aegypti Matthew DeGennaro, Ph.D. Chloe Goldman Laura Seeholzer Skin odor is a long-range, attractive cue that guides mosquitoes to their hosts. The mosquito perceives differences in skin odor, both between and within species, to determine which host to feed upon. The molecular mechanism by which mosquitoes translate host odor information into host-seeking behavior has been inferred but not demonstrated. To shed new light on mosquito olfaction and host-seeking behavior, we developed a technique for targeted mutagenesis in Aedes aegypti using zinc-finger nucleases. The establishment of loss-of-function genetics in Aedes aegypti opens new paths of investigation in vector biology including the neurobiology of host-seeking. We not only seek to understand how the mosquito responds to odor cues from the environment, but how its internal, nutritional status regulates odor perception. The transmission of vector borne disease involves female mosquitoes making behavioral shifts from host-seeking to oviposition to finding another host during each gonotrophic cycle. Understanding how these behavioral shifts are accomplished could open up new strategies for vector control. One of the advantages of Aedes aegypti is its clearly defined cyclical host-seeking behavior that is under humoral control. These behavioral changes have been correlated with alterations in antennal sensitivity to host-odor stimuli. We are in the process of identifying candidate genes that regulate the behavioral switch from host-seeking to oviposition. This project aims to (1) identify the olfactory receptors that mediate human skin odor perception and (2) determine the relationship between olfactory sensitivity and nutritional status during the gonotrophic cycle. The genetics of host specialization in the mosquito Aedes aegypti Lindy McBride, Ph.D. Laura Seeholzer Jermaine Watson, M.S. Outside of Africa, populations of the Yellow-Fever mosquito Aedes aegypti specialize on humans. They are strongly attracted to human scent, they thrive on human blood, and they breed in artificial containers in human-disturbed habitats - often even in water stored inside people's homes. Within Africa, however, many Aedes aegypti populations appear to be generalized. They are not particularly attracted to humans, they feed on a wide variety of animals, and they breed in tree holes in natural habitats. Previous work has shown that these two ecologically divergent forms of the mosquito coexist in several places along the coast of East Africa - one breeding in villages and the other breeding in surrounding forests. They appear to be maintaining ecological differences despite their close proximity. This project aims to (1) identify the genetic basis of ecological differentiation between the two forms and (2) to describe the evolutionary processes by which this differentiation is maintained. Click here for photos of Lindy McBride's Kenya mosquito collecting trip in January 2009. This work is funded in part by a grant to Richard Axel and L.B.V. from the Foundation for the National Institutes of Health through the Grand Challenges in Global Health Initiative Completed Projects Regulation of cellular and neuronal function by the Drosophila Ih channel Gabriel Gasque, Ph.D. Rhythmic cellular functions, such as the heartbeat and the timing of daily rhythms of activity and sleep, are regulated by the activity of cellular pacemakers. We are using genetic approaches to study the role of the Drosophila hyperpolarization- and cyclic nucleotide-gated ion channel, DmIh, in these processes. This is an ongoing collaboration with Dr. Gareth Tibbs at Columbia University and Dr. Michael Nitabach at Yale University. Genetic analysis of olfactory coding in Drosophila larvae Kenta Asahina Matthieu Louis, Ph.D. Silvia Piccinotti At an earlier developmental stage, Drosophila larvae display simple and robust olfactory-mediated chemotactic behavior controlled by 21 olfactory neurons expressing a repertoire of 25 odorant receptor genes. We have used a genetic approach to study odor coding in this simple animal by ablating specific sensory neurons and the receptors expressed in them, or by constructing animals with only a single functional olfactory neuron. By combining behavioral analysis with calcium imaging, we are attempting to understand the neural basis of olfactory behavior in this animal. click to enlarge Genetic and functional subdivison of the Drosophila antennal lobe. Elane Fishilevich Using genetic labeling of olfactory sensory neurons expressing a given receptor, we generated a nearly complete map connecting odorant receptor expression to olfactory neuron convergence to antennal lobe glomeruli in adult Drosophila. This work was supported in part by an individual F31 NRSA training grant from NIH/NIDCD to E.F. (5F31DC006795).