Surprise findings suggest mosquito odor sensors are sensitive to
molecular regulation to avoid insect repellents
Date:
March 16, 2022
Source:
Johns Hopkins Medicine
Summary:
In what they call surprise findings, scientists report that --
unlike fruit flies -- mosquitoes' odor sensing nerve cells shut
down when those cells are forced to produce odor-related proteins,
or receptors, on the surface of the cell. This 'expression' process
apparently makes the bugs able to ignore common insect repellents.
FULL STORY ==========================================================================
In what they call surprise findings, Johns Hopkins Medicine scientists
report that -- unlike fruit flies -- mosquitoes' odor sensing nerve
cells shut down when those cells are forced to produce odor-related
proteins, or receptors, on the surface of the cell. This "expression"
process apparently makes the bugs able to ignore common insect repellents.
==========================================================================
In contrast, when odor sensors in fruit flies are forced to express odor receptors, it prompts flight from some smelly situations.
The findings, published Mar. 8 in Cell Reports, reveal the variation in
insect olfactory systems, say the researchers, and add to the growing
body of research aimed at improving methods to repel mosquitoes from
human skin.
Mosquito bites not only create irritating swelling and itching, but,
worldwide, they play a role in spreading rampant and often lethal diseases
such as malaria and dengue fever, as well as Zika virus infections.
"When experiments don't go as predicted, there's often something new
to be discovered," says Christopher Potter, Ph.D., associate professor
of neuroscience at the Johns Hopkins University School of Medicine,
describing the new study. It turns out, he says, that, "Mosquitoes are so
much trickier than we thought." Potter and former postdoctoral fellow
Sarah Maguire, Ph.D., designed their research project suspecting they'd
find that mosquitoes have the same reaction as fruit flies when their
new odor sensors are forced to be expressed.
========================================================================== Other research showed that when odor receptors in fly olfactory neurons
are abnormally expressed, a new signal, based on the expressed odor
receptor, is delivered to the brain, and the bugs move away from an
offending odor.
The researchers then tested this same scenario on female Anopheles
mosquitoes, whose bite transmits parasites that cause malaria in
humans. The idea was that if researchers could push mosquito odor neurons
into a similar expression state, triggered by odorants already on the
skin, the mosquitoes would avoid the scent and fly off.
In the mosquito experiments, the researchers used mosquitoes genetically modified to overexpress an odor receptor called AgOR2, which responds
to animal odorants found on humans.
By measuring the neuron activity generated by mosquitoes' odor receptors,
the scientists found that the mosquitoes with overexpressed AgOR2
receptors had very little response to common animal scents, benzaldehyde
and indole, as well as chemical odorants in general.
"AgOR2 overexpression threw a wrench in the whole system by inactivating olfactory receptors in these mosquitoes," says Potter.
========================================================================== Next, working with Johns Hopkins scientist Loyal Goff, Ph.D.,
the researchers did additional experiments to determine the level of
messenger RNA output in olfactory neurons forced to express the AgOR2
gene, an indicator of the health of olfactory neurons.
They determined this by using a technique called RNA sequencing which
measures the amount of RNA, an intermediary between DNA and its protein
output, in neurons found in the antennae of normal and the genetically
modified mosquitoes.
They found that mosquitoes genetically modified to overexpress AgOR2
had up to 95% less expression in their natural olfactory receptors as
compared with unmodified mosquitoes.
Finally, in the current study, the researchers tested how mosquitoes
modified to overexpress AgOR2 responded to odorants in common insect repellents, such as lemongrass. They found that the genetically modified mosquitoes were able to ignore insect repellents.
The researchers suspect that the odor receptor shutdown may be a kind of failsafe in mosquitoes, ensuring that only one type of odorant receptor
is expressed at a single time.
Since Anopheles mosquito olfactory systems continue to develop into
adulthood, about eight days after hatching, the researchers speculate that
the insects' olfactory neurons might be susceptible to which olfactory receptors to express, based on their surrounding environment. This type
of flexibility in a mosquito's olfactory neurons may allow the mosquito to adapt to its odor environment. The researchers are conducting experiments
to test this theory.
Potter hopes that the current findings may advance the search for methods
that can trick the mosquito olfactory system into no longer preferring
the smell of humans.
The study was supported by the National Institutes of Health (NIAID R01Al137078), the Department of Defense, a Johns Hopkins Malaria Research Institute Postdoctoral Fellowship, the Johns Hopkins Malaria Research
Institute and Bloomberg Philanthropies.
========================================================================== Story Source: Materials provided by Johns_Hopkins_Medicine. Note:
Content may be edited for style and length.
========================================================================== Related Multimedia:
* Olfactory_neurons_in_mosquito_antennae ========================================================================== Journal Reference:
1. Sarah E. Maguire, Ali Afify, Loyal A. Goff, Christopher J. Potter.
Odorant-receptor-mediated regulation of chemosensory gene expression
in the malaria mosquito Anopheles gambiae. Cell Reports, 2022; 38
(10): 110494 DOI: 10.1016/j.celrep.2022.110494 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/03/220316132711.htm
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