Control of cell migration in the development of the posterior lateral line: antagonistic interactions between the chemokine receptors CXCR4 and CXCR7/RDC1

BACKGROUND: The formation of the posterior lateral line of teleosts depends on the migration of a primordium that originates near the otic vesicle and moves to the tip of the tail. Groups of cells at the trailing edge of the primordium slow down at regular intervals and eventually settle to differentiate as sense organs. The migration of the primordium is driven by the chemokine SDF1 and by its receptor CXCR4, encoded respectively by the genes sdf1a and cxcr4b. cxcr4b is expressed in the migrating cells and is down-regulated in the trailing cells of the primordium. sdf1a is expressed along the path of migration. There is no evidence for a gradient of sdf1a expression, however, and the origin of the directionality of migration is not known. RESULTS: Here we document the expression of a second chemokine receptor gene, cxcr7, in the migrating primordium. We show that cxcr7 is highly expressed in the trailing cells of the primordium but not at all in the leading cells, a pattern that is complementary to that of cxcr4b. Even though cxcr7 is not expressed in the cells that lead primordium migration, its inactivation results in impaired migration. The phenotypes of cxcr4b, cxcr7 double morphant embryos suggest, however, that CXCR7 does not contribute to the migratory capabilities of primordium cells. We also show that, in the absence of cxcr4b, expression of cxcr7 becomes ubiquitous in the stalled primordium. CONCLUSION: Our observations suggest that CXCR7 is required to provide directionality to the migration. We propose that directionality is imposed on the primordium as soon as it comes in contact with the stripe of SDF1, and is maintained throughout migration by a negative interaction between the two receptors

4D compressive sensing holographic imaging of small moving objects with multiple illuminations

International audienceIn previous work [Opt. Lett. 44, 2827 (2019)], we presented a method based on digital holography and orthogonal matching pursuit, which is able to determine the 3D positions of small objects moving within a larger motionless object. Indeed, if the scattering density is sparse in direct 3D space, compressive sensing algorithms can be used. The method was validated by imaging red blood cell trajectories in the trunk vascular system of a zebrafish (Danio rerio) larva. We give here further details on the reconstruction technique and present a more robust version of the algorithm based on multiple illuminations

Zebrafish Models to Study New Pathways in Tauopathies

International audienceTauopathies represent a vast family of neurodegenerative diseases, the most well-known of which is Alzheimer’s disease. The symptoms observed in patients include cognitive deficits and locomotor problems and can lead ultimately to dementia. The common point found in all these pathologies is the accumulation in neural and/or glial cells of abnormal forms of Tau protein, leading to its aggregation and neurofibrillary tangles. Zebrafish transgenic models have been generated with different overexpression strategies of human Tau protein. These transgenic lines have made it possible to highlight Tau interacting factors or factors which may limit the neurotoxicity induced by mutations and hyperphosphorylation of the Tau protein in neurons. Several studies have tested neuroprotective pharmacological approaches. On few-days-old larvae, modulation of various signaling or degradation pathways reversed the deleterious effects of Tau mutations, mainly hTauP301L and hTauA152T. Live imaging and live tracking techniques as well as behavioral follow-up enable the analysis of the wide range of Tau-related phenotypes from synaptic loss to cognitive functional consequences

Improvement of Cell Penetrating Peptide for Efficient siRNA Targeting of Tumor Xenografts in Zebrafish Embryos

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Imagerie 4D de la circulation sanguine chez la larve du poisson-zèbre par holographie numérique en illumination multiple

International audienceUne configuration de microscopie holographique qui utilise trois faisceaux d'illumination est proposée. Elle permet d'imager en 3D la positions des globules rouges en mouvement à partir d'un hologramme, ainsi que la structure 3D des vaisseaux sanguins perfusé à partir d'une séquence d'hologrammes

4D compressive sensing holographic microscopy imaging of small moving objects

International audienceWe show that compressive sensing (CS) calculations are very ecient to reconstruct in 3D sparse objects whose 2D hologram has been recorded by digital holographic microscopy. The method is well adapted to image small scattering objects moving within a larger motionless object. This situation corresponds to red blood cells (RBCs) circulating in the vascular system of a zebrash (Danio rerio) larva. RBCs positions are imaged in 3D from a single hologram, while the RBCs trajectories, i.e. the perfused blood vessels, are imaged from a sequence of holograms. With respect to previous work (Donnarumma et al., Opt. express, 24, 26887, 2016), we get a gain of ∼ 500 in calculation speed

Neuroprotective brain-derived neurotrophic factor signaling in the TAU-P301L tauopathy zebrafish model

International audienceBrain-derived neurotrophic factor (BDNF) dysregulations contribute to the neurotoxicity in neurodegenerative pathologies and could be efficiently targeted by therapies. In Alzheimer's disease (AD), although the relationship between BDNF and amyloid load has been extensively studied, how Tau pathology affects BDNF signaling remains unclear. Using the TAU-P301L transgenic zebrafish line, we investigated how early Tau-induced neuro-toxicity modifies BDNF signaling. Alterations in BDNF expression levels were observed as early as 48 h post fertilization in TAU-P301L zebrafish embryos while TrkB receptor expression was not affected. Decreasing BDNF expression, using a knockdown strategy in wild-type embryos to mimic Tau-associated decrease, did not modify TrkB expression but promoted neurotoxicity as demonstrated by axonal outgrowth shortening and neuronal cell death. Moreover, the TrkB antagonist ANA-12 reduced the length of axonal projections. Rescue experiments with exogenous BDNF partially corrected neuronal alterations in TAU-P301L by counteracting primary axonal growth impairment but without effect on apoptosis. Importantly, the axonal rescue was proved functionally effective in a behavioral test, at a similar level as obtained with the GSK3β inhibitor LiCl, known to decrease TAU phos-phorylation. Finally, treatment with a TrkB agonist, 7,8-dihydroxyflavone, led to comparable results and allowed full rescue of locomotor response. We provided here strong evidence that Tau neurotoxicity provoked alterations in BDNF system and that BDNF pathway might represent an efficient therapeutic target

Periodic mesoporous ionosilica nanoparticles for dual cancer therapy: Two-photon excitation siRNA gene silencing in cells and photodynamic therapy in zebrafish embryos

International audiencePhotodynamic therapy (PDT) and photochemical internalization (PCI) are two methods that use light to provoke cell death or disturbance of cellular membranes, respectively, via excitation of a photosensitizer and the formation of reactive oxygen species (ROS). In this context, two-photon excitation (TPE) is of high interest for PCI and/or PDT due to spatiotemporal resolution of two-photon light and deeper penetration of near-infrared light in biological tissues. Here, we report that Periodic Mesoporous Ionosilica Nanoparticles (PMINPs) containing porphyrin groups allow the complexation of pro-apoptotic siRNA. These nano-objects were incubated with MDA-MB-231 breast cancer cells, and TPE-PDT led to significant cell death. Finally, MDA-MB-231 breast cancer cells were pre-incubated with the nanoparticles and then injected in the pericardial cavity of zebrafish embryos. After 24 h, the xenografts were irradiated with femtosecond pulsed laser and the size monitoring by imaging showed a decrease 24 h after irradiation. Pro-apoptotic siRNA was complexed with the nanoparticles and incubation with MDA-MB-231 cells did not lead to cancer cell death in dark conditions, but with two-photon irradiation, TPE-PCI was observed and a synergic effect between pro-apoptotic siRNA and TPE-PDT was noticed, leading to 90% of cancer cell death. Therefore, PMINPs represent an interesting system for nanomedicine applications

Sigma-1 Receptor Is Critical for Mitochondrial Activity and Unfolded Protein Response in Larval Zebrafish

International audienceThe sigma-1 receptor (S1R) is a highly conserved transmembrane protein highly enriched in mitochondria-associated endoplasmic reticulum (ER) membranes, where it interacts with several partners involved in ER-mitochondria Ca2+ transfer, activation of the ER stress pathways, and mitochondria function. We characterized a new S1R deficient zebrafish line and analyzed the impact of S1R deficiency on visual, auditory and locomotor functions. The s1r+25/+25 mutant line showed impairments in visual and locomotor functions compared to s1rWT. The locomotion of the s1r+25/+25 larvae, at 5 days post fertilization, was increased in the light and dark phases of the visual motor response. No deficit was observed in acoustic startle response. A critical role of S1R was shown in ER stress pathways and mitochondrial activity. Using qPCR to analyze the unfolded protein response genes, we observed that loss of S1R led to decreased levels of IRE1 and PERK-related effectors and increased over-expression of most of the effectors after a tunicamycin challenge. Finally, S1R deficiency led to alterations in mitochondria bioenergetics with decreased in basal, ATP-linked and non-mitochondrial respiration and following tunicamycin challenge. In conclusion, this new zebrafish model confirmed the importance of S1R activity on ER-mitochondria communication. It will be a useful tool to further analyze the physiopathological roles of S1R