• Surprise findings suggest mosquito odor

    From ScienceDaily@1:317/3 to All on Wed Mar 16 22:30:42 2022
    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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