In vertebrate and invertebrate brains, neurons establish regionally distinct circuit architectures. Astrocytes are crucial elements in this environment, displaying remarkably elaborate, yet specific branching patterns. However, how astrocytes acquire their diverse morphologies in interaction with neurons and how these shape neuronal morphologies and function remains poorly understood. Our study will use the Drosophila visual system as an in vivo model, focusing on the interactions of neurons and astrocyte-like glia in the medulla. The latter establish stereotypic columnar and layer-specific branching patterns during development. Previously, we have shown that the glial-specific transmembrane Leucine-rich repeat protein Lapsyn is required for astrocyte branch extension into the synaptic neuropil. Using label-free mass spectrometry, we isolated a member of the Innexin family as one potential binding partner of Lapsyn. Based on our genetic analysis, we hypothesize that neuron subtypes engage in a dialog with astrocytes through gap junctions, that are stabilized by Lapsyn, to establish correct local glial morphologies. These in turn could refine neuronal development and function. In this integrative project from development to function, we will employ tailored genetic tools to achieve cell-type specific labeling and gene manipulations, as well as high-resolution and functional imaging. Specifically, our aims are (1) to characterize the developing neuron-astrocyte interface in the context of gap junction communication with specific neuron subtypes, (2) to assess the dynamic behavior of astrocyte branches during development, and (3) to examine how astrocyte branches shape synaptic connectivity and functional neuronal properties such as neurotransmitter recycling and axon initial segment proteins.

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Gas-phase chemical reactions are important in a wide variety of environments such as combustion, Earth’s atmosphere, and dense interstellar clouds. Modelling such environments requires a detailed understanding of the mechanisms and rate coefficients of key reactions that define the system. In the atmosphere, the oxidation mechanism of volatile organic compounds (VOC) influences on a regional scale the air quality and hence human health. On a global scale it affects the oxidizing capacity of the atmosphere and with this the global climate by controlling the lifetime of greenhouse gases such as methane and formation of tropospheric ozone. Peroxy radicals are key intermediates in all oxidation reactions, however their reactivity is still not well understood. The current project aims at investigating this chemistry using different experimental approaches. Both PIs have set-up worldwide unique techniques dedicated to the sensitive and selective detection of these radicals: Laser photolysis coupled to time-resolved cavity ring down technique in Lille and laser photolysis coupled to time-resolved double frequency comb spectroscopy. In the frame of this project we want to further improve the experimental techniques to even better study key reactions: in Lille we will develop a new double-walled photolysis reactor which can be (a) thermostated to temperatures of atmospheric interest (the current reactor can only be heated) and (b) add a detection path based on broadband UV absorption spectroscopy. In Taiwan, 2 new laser sources will be added to extend the accesible wavelength range for the already existing frequency comb spectroscopy.

To construct complicated neural networks, glial cells migrate to their final destination to interact with neurons, either solitarily or in a group. Group or collective migration demands cell-cell communication as well as several intracellular mechanisms for reiterative processes during cell migration. In addition, collective behaviors imply dynamic and fine-tuning control of specific molecular pathways. Protein degradation by the ubiquitin proteasome system regulates key biological processes including cell cycle progression and signaling pathways. In a collaborative study between the two groups, we demonstrated that cullin-RING ubiquitin ligases (CRLs) regulate the protein levels of the glial fate determinant Gcm during Drosophila glial differentiation. We also made a preliminary observation that the protein degradation machinery impacts on glial migration. In addition, we have recently found that the levels of Gcm directly affect glial migration in a linear manner, that is, the more Gcm the more efficient the migration. Building upon these results, we propose to study the role of protein ubiquitination in collective migration using an in vivo model that is suitable for genetic analyses: the glial cell chain present in the Drosophila wing. The fast and precise control of protein levels/activity indeed makes the ubiquitination pathway an ideal candidate for the regulation of collective migration. On one side, the role of Gcm dosage in collective migration will be established by a live-imaging system. On the other side, the role of the ubiquitin proteasome system in collective glial migration will be studied to determine the involvement of specific degradation pathways. Genetic and biochemical studies will further elucidate how Gcm ubiquitination and degradation control collective glial migration. Finally, particular E3 ligases involved in collective glial migration will be identified. This collaborative proposal will be performed in both laboratories with the French group focusing on the live imaging and phenotypical analysis of the migration behaviors and the Taiwanese group on genetic and biochemical study of protein ubiquitination and degradation by E3 ligases. Videoconferences and bilateral lab meetings will be held regularly to monitor the progress and ensure the success of the collaboration. At the end of the collaborative grant, we will organize a symposium to promote interaction and collaboration for scientists from France and Taiwan. The project represents a revised application (BLI ANR 2011) that was very well perceived. The reviewers acknowledged the quality, the novelty and the originality of the proposed work. They also recognized the complementarity of the two teams and the fact that the proposed project stems form previous, collaborative work ("the two groups have completely complementary expertise so that neither the French nor the Taiwanese group could perform the proposed analysis on their own despite their excellent track records. The project therefore generates true added value. The consortium is unique in its expertise. Moreover, the consortium has already proven its effectiveness in the past as shown by their collaborative paper in PNAS in 2009"). The revised application complies with the request of a balanced effort and more exchanges between the two laboratories. In addition, a student Pei-Yi Chen, who is currently a master thesis student in National Yang Ming University, will work on this project. She will apply to PhD programs in both Taiwan and France and mentored by both PIs. Finally, a postdoc from the French group will stay in Taiwan for one year.