Featured image with Julien Rességuier

Our featured image, acquired by Julien Rességuier, shows the branchial cavity lymphoid architecture of an adult zebrafish. It is a 2D projection of a 3D multi-field of view acquisition of a transversal cryosection (30 μm) that has been stained with fluorescent phalloidin (inverted LUT – grey/copper) and DAPI (blue) to reveal tissue structures and labelled with an anti-ZAP70 antibody to reveal T / natural killer (NK) cells (cyan). The pharynx (top left) is connected to the branchial cavity (middle) in which a gill arch is visible. The tree-like structures are the filaments and lamellae of the gills, where gas exchange occurs. Below the pharynx (left), the sub-pharyngeal isthmus separates the two branchial cavities located on each side of the fish head. Recently characterized (https://www.science.org/doi/10.1126/sciadv.adj0101), the branchial cavity lymphoid architecture includes the Nemausean Lymphoid organ (NELO) along the sub-pharyngeal isthmus, Amphibranchial Lymphoid Tissues (ALT) on each side of gills arches, and Interbranchial Lymphoid tissues (ILT) located in-between opposite filaments. The acquisition has been deconvolved using an iterative algorithm (14 iterations). An inverted LUT has been applied to display the signal associated with phalloidin to facilitate the distinction between the numerous tissue structures.

Find out more about Julien’s research below:

Research career so far: I completed my PhD in 2017 at the University of Lyon 1 using the zebrafish model to study therapeutic nanoparticles.  I then did a postdoc at the University of Oslo with Professor Gareth Griffiths studying the cell biology aspect of nanomedicines using fish models of human diseases. On the side of my postdoc, I also worked on characterizing the spatial organization of the fish immune system. It is at this time that I further developed my skills in microscopy and sample preparation, for which I received several awards from the Nikon Small World Competitions in 2022. After my postdoc, I worked for 6 months as researcher with Professor Finn-Eirik Johansen and Professor Shuo-Wang Qiao at the University of Oslo, working on the cod immune system. Both professors then hosted me as guest researcher for 1.5 years, which allowed me to advance my own projects leading to a publication in Science Advances presenting the discovery of a lymphoid organ in fish that is reminiscent of mammalian tonsils (https://www.science.org/doi/10.1126/sciadv.adj0101).  

Current research: I am now a group leader at the University of Oslo, department of Biosciences, thanks to the Research Council of Norway which recently awarded me with a highly competitive Young Research talent grant. My research interests are on the spatial dynamics of immune responses & regulation, with a particular emphasis on the branchial cavity lymphoid architecture of fish and nanomedicines. An important research axis is the characterization of the newly discovered Nemausean Lymphoid organ. In addition, I am also continuing my research on how therapeutic nanoparticles reach diseased area using fish models of human diseases.

Favourite imaging technique/microscope: I am a heavy user of spinning-disk confocal microscopes (Andor Dragonfly 500 and Olympus IXplore), which in my opinion provide an advantageous balance between efficiency and practicality. I can extract as much data  as I can from my samples in a small amount of time. I mostly use them for 3D multi-field of view imaging of thick cryosections and for live-imaging of zebrafish larvae at high spatial and temporal resolution. I am adept at using non-conventional LUT to find the perfect balance between displaying scientific information and beauty. Currently, I am combining imaging skills with wholemount imaging and clearing techniques in order to study the immune system in all its spatial complexity.

What are you most excited about in microscopy? I am particularly excited by the advances in light-sheet microscopy for imaging large samples at high spatial and temporal resolution. Although sample preparation might be more challenging, with better imaging quality, faster acquisitions, increased field of investigation, what is not to like! Doing a lot of 3D imaging, I am particularly excited about the development of virtual reality to analyse 3D images. I believe this will provide major advances for image analysis in the years to come.

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