Research Interests 

The Molecular Genetics of Olfaction in Insect Disease Vectors

The major focus of the laboratory is the characterization of specific genes and their products that control important behavioral processes in the life cycle of insects which act as disease vectors. In this light we concentrate on host (i.e. blood-meal source) seeking/selection in the mosquito Anopheles gambiae which is the principal vector for malaria in Africa. Malaria is caused by a protozoan parasite of the genus Plasmodium that is transmitted to humans through blood feeding by female Anopheline mosquitoes. In this context, we are examining the molecular events of olfaction as this sense predominates the overall host preference behaviors in mosquitoes and other insects. This aspect of the mosquito's behavior is especially important as it makes a significant contribution to the vectorial capacity of this arthropod vector, as well as playing a similar role in the overall impact of many other insects of economic importance.

 

The Molecular Components of Olfactory Signal Transduction in Insects

The proteins that are graphically represented here are present on the inside surface of the olfactory receptor neuron (ORN) dendritic membrane on olfactory receptor neurons. Signal transduction is initiated when odorants (either alone or in complexes with Odorant Binding Proteins) bind to members of seven transmembrane containing odorant receptors (ORs). Originally thought to be G-protein coupled, insect ORs are now almost universally recognized to be novel signaling complexes that combine ligand specificity subunit (conventional ORs) with a widely- expressed, non-conventional OR subunit that most probably acts as a direct ionotropic channel on ORN dendrites- in fruitflies this OR is known as 83b (in light of its position on polytene chromosomes) while in mosquitoes this common component is called OR7. Recent studies in Drosophila (Benton et. al. 2009) have also pointed to the existence of a novel class of chemosensory receptors known as ionotropic receptors (IRs) that have homology to insect glutamate receptors.  Current efforts are focused on understanding how ORs, IRs, OBPs and other components of this pathway mediate olfactory signal transduction in anopheline mosquitoes.

We use molecular and informatics based approaches to identify genes that are active in olfactory signal transduction in An. gambiae and other disease vector mosquitoes. The molecular characterization of genes which mediate olfaction in this Anopheline mosquito has started with the generation of cDNA libraries specifically derived from olfactory (i.e. the antennal and maxillary palps) and neural (heads that have been stripped of antennal and maxillary palps) structures of female adult mosquitoes. These hand-dissected structures have been used as substrate for the synthesis of subtracted cDNA libraries using novel PCR based methods that are specifically designed to facilitate the use of picogram amounts of mRNA starting material. More recently we have focused on genomics based approaches that include genome mining and deep sequencing of olfactory transcriptomes that has thus resulted in the isolation of several olfactory genes from An. gambiae that are currently being characterized at the molecular and cellular levels.

Much of the lab’s focus is on the molecular, biochemical and functional characterization of ORs An. gambiae (AgORs). Over the years "Team AgOR" has gone from the original characterization of AgORs insofar as their DNA sequence and organization to detailed in vivo expression studies. We have extended this study to include the use of ex vivo expression systems, electrophysiology, cell culture and transgenic insect systems (e.g.Drosophila) in order to study the functional characteristics of AgORs from specific senory appendages to whole genome wide approaches (see publication list).

A long-term objective of our work is the molecular characterization of the olfactory genes in general as well as the mechanisms that which are central in the marked preference for human blood meals (anthropophily) characteristic of An. gambiae s.s. In fact it is this component of the mosquito's behavior which makes it such an important disease vector. In contrast, a preference for bovine blood meals (zoophily) has been observed in the non-vector sibling species An. quadriannulatus. By using subtractive hybridization it may be possible to prepare anthropophilic and zoophilic enriched cDNA pools from which a more defined pool of olfactory and other behavioral genes may be isolated. For the present, we are engaged in a suite of studies to isolate and characterize orthologous ORs from species of anthropophilic and zoophilic mosquitoes as well as from other mosquito vectors for other human pathogens. These include Aedes aegypti, the vector for dengue and yellow fever that is widespread in Central and South America and Culex pipens, the North American mosquito responsible for transmission of West Nile Virus.

On the applied side, we are privileged to lead a broad international network of five laboratories (encompassing Yale University, New Haven, CT; Wageningen University, The Netherlands; ICIPE, Kenya; The MRC Laboratories, The Gambia) that has been selected for a $8.9M Grand Challenge In Global Health grant for the specific purpose to target odorant receptors in order to design a new generation of mosquito repellents and attractants. Together with colleagues at the Vanderbilt Institute for Chemical Biology we are engaged in using state of the art molecular and chemical approaches that target AgOR/AaORs in order to design a new generation of mosquito repellents and attractants that would foster the design of novel programs that target chemosensory pathways and the behaviors they control in vector mosquitoes. These may also include behavioral disruption programs based on specific inhibitors (aka “confusants”) of OR-mediated olfactory pathways as well as the identification and intelligent design of novel and economically synthesized mosquito attractants and repellents. This approach could be extended to other mosquito vectors as well where reductions in host seeking (through the use of confusants or repellants) could potentially effect disease transmission by targeting adult vectorial capacity. Attractants may be incorporated into novel mosquito management strategies, these include: lures to increase the efficiency of traps for sentinel monitoring of vector populations and insecticide-laden mosquito trapping systems for population reduction; augmentation of insecticide-treated net (ITN)-based strategies as well as otherwise enabling innovative insect/disease control strategies that focus on disrupting and/or taking advantage of vector-host interactions.

We collaborate in these efforts with several other laboratories at Yale University (John Carlson), University of Florida (Barry Ache), University of Miami (Chuck Luetje) the Swedish Agricultural University (Bill Hansson/Rickard Ignell) and The University of Wageningen (Willem Takken).