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https://univ-cotedazur.zoom.us/j/86224312671?pwd=b1BZcHcrQ3BLQXNjZnRFQWhiNnZ5UT09

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Abstract :

In nature, metazoans co-habit with micro-organisms and have evolved tight relationships with them. The exposure to microbes not only impacts the physiology of animals but also their behavior. Indeed, exposure to harmful microbes can lead to the canonical immune response as well as to behavioral response which function could be to reduce the exposure to the pathogen or avoid its spread. We studied the molecular and cellular mechanisms underlying behavioral responses to bacterial exposure and in particular to bacterial peptidoglycan. The latter is a component of the bacterial cell wall and the main elicitor of the NF-kB immune pathway in Drosophila melanogaster. Detection of peptidoglycan was previously associated with a decrease in egg-laying in infected flies. This decrease depends on the activation of the NF-kB immune pathway in neurons (Kurz, C.L., Charroux, B. et al.,2017). We identified the neurons responsible for this behavioral response. In particular, we identified a couple of octopaminergic neurons in the fly brain that modulate egg-laying upon peptidoglycan exposure via the NF-kB immune pathway. Moreover, the identified neurons directly sense the bacterial peptidoglycan and this sensing leads to their decreased activity (Masuzzo, A. et al.,2019).

 Additionally, we showed that bacterial peptidoglycan is also detected by two classes of taste sensory neurons. In in vivo calcium imaging, taste neurons for the detection of bitter compounds respond to bacterial peptidoglycan and this response is dependent on some elements of the NF-κB cascade. Furthermore, taste neurons for the detection of sweet compounds also respond to peptidoglycan. However, in this case, the response is independent of the NF-κB pathway. Thus, the integration of signals coming from these two neuronal classes might be necessary for the fly to make feeding decisions.

Taken together, our current model is that the same bacterial elicitor (peptidoglycan) dually induces the NF-kB signaling pathway in immune-competent cells and neurons, and thus triggers both canonical and behavioral immunity. However, some neurons, i.e. taste sweet neurons, respond to peptidoglycan in an NF-kB independent way, suggesting that other mechanisms are required for the peptidoglycan detection in these neurons.

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