Here are the exciting projects currently being carried out by PhD students and Postdoctoral Fellows in the Vosshall Lab.
Processing Human Cues in the Mosquito Brain – Meg Younger PhD
Models of multi-sensory integration in the antennal lobe of the female mosquito
Female mosquitoes require a blood-meal for reproduction, and show intense attraction to human hosts. They rely on host sensory cues, including carbon dioxide (CO2) in breath, and components of human body odor, such as lactic acid. These stimuli alone elicit little or no attraction, but in combination they synergize to trigger host-seeking behavior.
It is unknown where and how any human host cues are represented in the mosquito brain. It is also unknown how human host cues synergize to drive host attraction and ultimately trigger biting behavior. To address these questions I am using two-photon excitation microscopy and electrophysiology to measure activity in the mosquito central nervous system. I am focusing on the antennal lobe of the brain, a region that is an important site of odor processing in other insects.
mosquitobrains.org: An Online Atlas of the Brain of Aedes aegypti – Meg Younger PhD
Female mosquito brain
As a tool to understand the neural circuitry that underlies mosquito behavior, we have generated a reference brain for Aedes Aegypti. This is the brain from a female mosquito that has different brain regions annotated for viewing in an online browser. 3D-reconstructions are also available for viewing. Brains imaged on a confocal microscope can be registered onto the female reference brain with a free and open source software pipeline, which is available at mosquitobrains.org. This will allow users to examine how expression patterns of new transgenic lines intersect. Lastly, this website will serve as a repository for mosquito neuroanatomy data, as new transgenic reagents are generated in this rapidly growing field.
The role of host physiology in mosquito attraction – Maria Elena De Obaldia PhD
Model of physiological factors that may contribute to mosquito attraction to vertebrate hosts.
Unlike most insect species, which feed on plants, female mosquitoes require a vertebrate blood meal to produce each batch of eggs. This mosquito blood-feeding behavior facilitates disease transmission among populations because females feed on multiple humans throughout their lifetime. There is intense interest in developing interventions to diminish mosquito attraction to humans, thus limiting the spread of mosquito-borne disease.
Mosquitoes use multimodal sensory cues to locate human hosts in their environment, including heat, CO2, and human odor. Differences in skin odor alone can modulate mosquito attraction, when temperature and CO2 are held constant. Physiological factors that contribute to odors emanating from human skin are unclear, but may include: genetic factors, diet, immunity, blood metabolites, and the composition of skin microbiome. I will investigate the contribution of physiological factors to human odor and mosquito attraction using mice as model vertebrate hosts. These studies aim to identify mechanisms of mosquito host preference.
A Taste of Blood – Veronica Jové
When a female mosquito takes a blood meal from a human host, she uses the dedicated blood-feeding appendage, the stylet, to pierce skin and pump blood. The needle-like stylet contains female-specific cells and neuronal processess that may be used to detect blood
A female mosquito must take a blood meal from a vertebrate host to produce eggs, and in doing so she transmits diseases such as Zika. The mechanism by which a female detects blood and initiates this robust behavioral program is unknown. Early studies have demonstrated that protein is not sufficient or required to initiate blood-feeding, although it is essential for egg production. Surprisingly, ATP in saline is sufficient to initiate blood-feeding in the absence of blood components and chemosensory cues from skin. We hypothesize that the decision to engorge on blood is mediated by the rapid sensory detection of ATP as a proxy for blood. To elucidate how the detection of ATP leads to the initiation of blood-feeding behavior, we are focusing on the dedicated blood-feeding appendage, the stylet, which is the only innervated appendage that directly contacts blood. We are using behavior, genomics, and calcium imaging to identify the cells and receptors that detect ATP. We will use this information to map the circuitry that detects blood and regulates a behavior responsible for transmission of vector-borne diseases to millions of people across the globe.
Genes and Neural Circuits underlying Sexual Dimorphism in Mosquito Host-Seeking Behavior – Nipun Basrur
Sex-specific splicing of a representative gene and its expression pattern in male and female mosquito brains
A female mosquito is expertly adapted to find a vertebrate host to take a blood-meal, which she requires to develop her eggs. Only females carry out this specialized innate behavior. Since host-seeking and blood-feeding are sexually dimorphic behaviors, the underlying genes and neural circuits controlling them are likely also sexually dimorphic. I hypothesize that sex-specific splicing of key genes controls sexual dimorphism in host-seeking behavior. To test this, I have identified genes that are sex-specifically spliced in mosquito brains, and I am generating mutants that disrupt the sex-specific isoforms of each gene, and developing transgenic reagents to visualize the cells expressing these genes.
Encoding and modulation of Aedes aegypti mosquito host-seeking behavior by internal state – Margaret Herre
(A) A female Ae. aegypti mosquito engorges on a blood-meal from a human host. (B) The QF2-QUAS binary expression system drives expression of dTomato and GCaMP6s in olfactory sensory neurons in one of the mosquito olfactory organs, the antenna.
For my main thesis research, I am studying the role of the steroid hormone 20-hydroxyecdysone (20E) in regulation of mosquito host-seeking behavior. I have established that 20E suppresses host-seeking drive without affecting other feeding behaviors and have shown that receptor for 20E, the ecdysone receptor (EcR) is expressed in olfactory sensory neurons. I hypothesize that 20E is acting directly at the level of the sensory neuron to affect how female mosquitoes perceive human odor. EcR is a nuclear hormone receptor that is required for development. Since we currently are unable to generate a conditional EcR knockout mosquito, I am taking orthogonal approaches to determine the role of EcR and 20E signaling in sensory neurons. These experiments include determining the transcriptional signature of 20E signaling in olfactory organs with RNA-seq and labeling and manipulating EcR chemosensory neurons using the split QF2-QUAS binary expression system.
In collaboration with Meg Younger, a postdoc in our lab, I seek to understand how the mosquito olfactory system is organized. A fundamental molecular feature of olfactory systems is that individual neurons express only one olfactory receptor in each olfactory sensory neuron. In both mice and Drosophila, neurons that express the same olfactory receptor then converge in the same regions in the primary olfactory processing centers in the brain. This organization enables olfactory systems remarkable specificity. We made the surprising discovery that in Aedes aegypti, olfactory sensory neurons express multiple classes of olfactory receptors in each neuron. Our ongoing experiments are determining the functional significance at the level of the sensory neuron, as well as behavioral consequences for discriminating attractive and aversive odorants.
Sustained motivation during mosquito host seeking – Trevor Sorrells PhD
Chemosensory coding of DEET in Aedes aegypti tarsi – Olivia Goldman
An orco mutant female mosquito avoiding DEET-treated skin.
The insect repellent DEET is a synthetic compound, discovered in 1946 by the USDA as part of a large chemical screen. Since its discovery, DEET has become the most broadly used and effective arthropod repellent available, but the details of how DEET works remain elusive. We discovered that, in addition to being able to smell DEET, Aedes aegypti can detect DEET upon contact via their legs (Dennis et al, 2019). Using a combination of imaging techniques, molecular profiling, and genetic manipulation, we are further investigating the molecular mechanisms of DEET contact detection in the mosquito leg.
Mechanisms of a Lifetime of Behavior in Aedes aegypti Mosquito Females – Leah Houri-Ze’evi PhD
A three step process to study the epigenetic basis of the refractory state.
Female Aedes aegypti mosquitoes mate only once during their lifetime, after which they become refractory to any additional insemination attempts. This shift in behavior is robustly maintained throughout the lifetime of the female (up to 6 weeks) by an unknown mechanism. Although crucial to the understanding of mosquito reproduction and dispersal, little is known about the behavioral or the molecular processes by which females reject males for a lifetime after a single mating event. We would like to mechanistically test the hypothesis that distinct transcriptional and epigenetic changes create the different refractory components and maintain it for a lifetime. Such mechanisms have been linked in the past to social behavior and learning in multiple species and are compelling candidates for sustaining this life-long memory. Refractoriness in female mosquitoes provides a unique system for decoding neuronal and transcriptional changes that modify behavior permanently. Furthermore, understanding of the refractory state in female mosquitoes, and ideally manipulating it, could contribute to the success of controlling the spread of the deadliest animal on the planet.