Insecte

Résumé

Les Insectes () sont une classe d'animaux invertébrés de l'embranchement des Arthropodes et du sous-embranchement des Hexapodes. Ils sont caractérisés par un corps segmenté en trois tagmes (tête possédant des pièces buccales externes, une paire d'antennes et au moins une paire d'yeux composés ; thorax pourvu de trois paires de pattes articulées et deux paires d'ailes plus ou moins modifiées ; abdomen dépourvu d'appendices) contenant au maximum 11 segments protégés par une cuticule formant un exosquelette composé de chitine et pourvu de trachées respiratoires. Avec près de d'espèces décrites existant encore (et près de espèces inventoriées par an), les Insectes constituent 55 % de la biodiversité des espèces et 85 % de la biodiversité animale (définie par le nombre d'espèces). On estime entre 5 et d'espèces possibles. (10 milliards de milliards) d'individus seraient vivants en même temps à un instant donné selon des estimations. Leur biomasse totale serait 300 fois plus important

Source officielle

https://fr.wikipedia.org/wiki/Insecte

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Many insect species are associated with endosymbiotic bacteria which have the particularity of living within host tissues. Endosymbionts benefit from this stable and nutritious environment, while providing ecological advantages to their host, such as protection against parasites or thermal tolerance. Spiroplasma poulsonii is an endosymbiotic bacterium that infects natural populations of Drosophila melanogaster. Spiroplasma poulsonii lacks a cell wall, a fact that renders it invisible to the host immune system and allows it to thrive in the host hemolymph. It invades the female germline by co-opting the hostâs yolk transport and uptake machinery, which ensures its vertical transmission. Its efficient transmission is associated with a phenotype called male-killing, whereby infected male embryos die during their early development while infected females survive. The mechanisms that ensure the stability of Drosophila-Spiroplasma symbiosis are increasingly well understood, but the bacterial genes involved remain poorly known because of the intractability of Spiroplasma. This project aims at better characterizing the Drosophila-Spiroplasma interaction, with particular focus on the bacterial side. In the first part, I developed a method to cultivate Spiroplasma poulsonii in vitro by optimizing a commercially available medium. This culture method allowed comparing the transcriptome of in vitro grown versus host-grown Spiroplasma, enabling us to identify putative genes involved in the interaction with the host. Interestingly, inside its insect host, S. poulsonii up-regulates genes coding for toxins of the Ribosomal Inactivating Protein (RIP) family. RIPs were previously known for their role in host protection against macro-parasites, such as wasps and nematodes. Their up-regulation in unparasitized hosts compared to culture was thus peculiar, raising the question what effect these RIPs have on host biology. Thus, in the second part, I studied the function of S. poulsonii RIPs in the absence of parasites. I showed that two of them are constantly expressed within the host and provide evidence that these toxins shorten host life span and increase embryonic mortality. Interestingly, the expression of RIPs was more toxic to male embryos than females, suggesting that RIPs contribute to S. poulsonii-induced male-killing. Last, I studied the D. melanogaster response to RIPs, and how the host mitigates the deleterious effects of these toxins by up-regulating the cytosolic chaperone Heat-Shock-Protein 70B (HSP70B). This protein carries out essential functions in protein homeostasis under normal and stressful conditions such as folding, refolding, or increasing the half-life of proteins. Interestingly, up-regulation of Hsp70B in the presence of RIPs results in an increased lifespan and in a better tolerance to heat stress, which may be ecologically advantageous. Altogether, this work illustrates how Spiroplasma-derived RIP toxins can differentially affect Drosophila depending on the ecological context, ranging from beneficial upon parasite infection or heat shock to detrimental in the absence of such environmental pressures.

EPFL2018

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Trypanosomatid parasites are significant causes of human disease and are ubiquitous in insects. Despite the importance of Drosophila melanogaster as a model of infection and immunity and a long awareness that trypanosomatid infection is common in the genus, no trypanosomatid parasites naturally infecting Drosophila have been characterized. Here, we establish a new model of trypanosomatid infection in Drosophila-Jaenimonas drosophilae, gen. et sp. nov. As far as we are aware, this is the first Drosophila-parasitic trypanosomatid to be cultured and characterized. Through experimental infections, we find that Drosophila falleni, the natural host, is highly susceptible to infection, leading to a substantial decrease in host fecundity. J. drosophilae has a broad host range, readily infecting a number of Drosophila species, including D. melanogaster, with oral infection of D. melanogaster larvae resulting in the induction of numerous immune genes. When injected into adult hemolymph, J. drosophilae kills D. melanogaster, although interestingly, neither the Imd nor the Toll pathway is induced and Imd mutants do not show increased susceptibility to infection. In contrast, mutants deficient in drosocrystallin, a major component of the peritrophic matrix, are more severely infected during oral infection, suggesting that the peritrophic matrix plays an important role in mediating trypanosomatid infection in Drosophila. This work demonstrates that the J. drosophilae-Drosophila system can be a powerful model to uncover the effects of trypanosomatids in their insect hosts. IMPORTANCE Trypanosomatid parasites are ubiquitous in insects and are significant causes of disease when vectored to humans by blood-feeding insects. In recent decades, Drosophila has emerged as the predominant insect model of infection and immunity and is also known to be infected by trypanosomatids at high rates in the wild. Despite this, there has been almost no work on their trypanosomatid parasites, in part because Drosophila-specific trypanosomatids have been resistant to culturing. Here, we present the first isolation and detailed characterization of a trypanosomatid from Drosophila, finding that it represents a new genus and species, Jaenimonas drosophilae. Using this parasite, we conducted a series of experiments that revealed many of the unknown aspects of trypanosomatid infection in Drosophila, including host range, transmission biology, dynamics of infection, and host immune response. Taken together, this work establishes J. drosophilae as a powerful new opportunity to study trypanosomatid infections in insects.

American Society for Microbiology2015

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Methods for acute and long-term imaging of the ventral nerve cord in behaving adult Drosophila

Laura Joan Hermans

Understanding how neural circuits remodel and adapt to animal behavior is a central theme in the field of Neuroscience. One strategy to reach this goal is to repeatedly record the same animal's neural circuits and observe how they adapt when facing different challenges. Research has primarily focused on identifying neural circuits and connectivity maps within the brains of model organisms. Nevertheless, it has become evident that functional recordings are essential to have a complete understanding of how neural circuits generate behaviors. Numerous techniques have been introduced to record activity from brain circuits in model animals spanning from monkeys to insects. However, imaging the spinal cord in mammals or the ventral nerve cord in insects remains an open challenge due to the complexity of obtaining optical access without impacting the animal's behavior and damaging neural tissues. As a result, we have very limited information on how neural circuits in the spinal cord generate behaviors and how they adapt to different experiences such as injury or aging. Drosophila is a perfect model organism for carrying out this line of research thanks to its small size, genetically tractable nervous system, and behavioral diversity. The results are relevant to human physiology and behavior as many mechanisms have homologs in mammals. What is missing is a technological advancement that allows recording of behavior, structural changes in the circuits, and spatiotemporal dynamics of neural activity on the same animal.This thesis addresses this gap and introduces two novel methods for in vivo functional recordings of the fly's ventral nerve cord (VNC). The first one gains short-term access to the fly's VNC using a novel dissection preparation. The second one enables long-term functional recordings of the fly's VNC thanks to a toolkit combining four microengineered devices: a surgical arm, a V-shape implant, an optically transparent and numbered window and a remounting stage. The toolkit is suitable for both male and female flies and provides optical access to the VNC for at least one month. Additionally, the long-term toolkit does not impact flies' behaviors compared to intact flies and can be used to image both sparse and large populations of neural activity in flies' cervical connective and VNC. The toolkit was tested in two proof-of-concept (POC) applications. In the first POC, the toolkit monitored the degradation of sensory neurons in the VNC over weeks following limb amputation. In the second POC, the toolkit monitored global changes in neural dynamics following ingestion of a high-concentration caffeine solution. In conclusion, this thesis introduces new techniques for functional recordings of the fly's cervical connective and VNC over short and long time scales. They enable optical access to the fly's cervical connective that can be leveraged to study the content of information transmitted between the brain and the VNC while the fly is behaving. The two POCs demonstrate that the novel technology is ideally suited for long-term experiments and could be applied to a wide range of studies. For instance, the toolkit could be used to investigate how behaviors are encoded in the fly's VNC and how they adapt over time to experiences such as disease, aging, drug intake and learning.

EPFL2022

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Methods for acute and long-term imaging of the ventral nerve cord in behaving adult Drosophila

Laura Joan Hermans

EPFL2022

American Society for Microbiology2015

EPFL2018