It is known that all living organisms adapt their behaviour in response to infection, however, the mechanisms behind this are less understood. Recent studies in fruit flies have begun to unravel these behaviours, showing, for example, that flies can lay fewer eggs in response to bacterial infection. Now, a study led by researchers at Aix-Marseille Université shows an example of manual body regulation where neurons modulate egg production in response to bacterial infection in fruit flies. The team state that their findings represent a case of ‘behavioural immunity’ in response to bacterial infection, and that in addition to triggering conventional antibacterial weaponry, fruit flies use nerve cell signalling pathways to reduce the impact of infection on their offspring and their environment. The opensource study is published in the journal eLife.
Previous studies show that in addition to developing strategies to reduce infection, animals can engage in behaviours which lower the impact of the infection. Earlier studies from the group showed that following bacterial infection in fruit flies, there was a temporary reduction in their egg-laying activity. It is known that peptidoglycan, a component of the bacterial cell wall, activates the NF-kB pathway, which controls the immune response in the fruit fly. The lab found that injection of purified peptidoglycan into the flies also affects egg-laying, suggesting that the same bacterial component regulates both immune and behavioural responses to bacteria. The current study investigates exactly how egg-laying in fruit flies is altered based on the discovery that peptidoglycan also activates the NF-kB pathway to control egg-laying.
The current study shows that flies with infections had three times as many mature eggs in the ovary as uninfected flies. Results show that as egg-laying resumes after 24 hours, the infection temporarily blocks the release of the eggs into the oviduct. Data findings show that peptidoglycan is sensed by neurons, which carefully controls the process, to ensure that normal egg-laying resumes once the threat of infection has passed.
Results show that the neurons which produce octopamine, a key neurotransmitter involved in ovulation, are the ones that sense peptidoglycan to regulate egg-laying. Data findings show the peptidoglycan dependent NF−κB pathway activation in octopaminergic neurons is the molecular signal which triggers the decrease of egg-laying post infection.
The team surmise that their findings show that bacterial infection regulates ovulation by affecting the octopaminergic signalling pathway in neurons, via activation of the NF-kB pathway. For the future, the researchers state that they plan to test whether this neuronal response to peptidoglycan following infection also occurs in the neurons of higher organisms.
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