Identification and in vivo functional investigation of a HOMER2 nonstop variant causing hearing loss

DFNA68 is a rare subtype of autosomal dominant nonsyndromic hearing impairment caused by heterozygous alterations in the HOMER2 gene. To date, only 5 pathogenic or likely pathogenic coding variants, including two missense substitutions (c.188 C > T and c.587 G > C), a single base pair duplication (c.840dupC) and two short deletions (c.592_597delACCACA and c.832_836delCCTCA) have been described in 5 families. In this study, we report a novel HOMER2 variation, identified by massively parallel sequencing, in a Sicilian family suffering from progressive dominant hearing loss over 3 generations. This novel alteration is a nonstop substitution (c.1064 A > G) that converts the translational termination codon (TAG) of the gene into a tryptophan codon (TGG) and is predicted to extend the HOMER2 protein by 10 amino acids. RNA analyses from the proband suggested that HOMER2 transcripts carrying the nonstop variant escaped the non-stop decay pathway. Finally, in vivo studies using a zebrafish animal model and behavioral tests clearly established the deleterious impact of this novel HOMER2 alteration on hearing function. This study identifies the fourth causal variation responsible for DFNA68 and describes a simple in vivo approach to assess the pathogenicity of candidate HOMER2 variants.

Periodic Mesoporous Ionosilica Nanoparticles for Dual Cancer Therapy: Two-Photon Excitation siRNA Gene Silencing in Cells and Photodynamic Therapy in Zebrafish Embryos

Photodynamic 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 hours, 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.

Developmental exposure to the A6-pesticide causes changes in tyrosine hydroxylase gene expression, neurochemistry, and locomotors behavior in larval zebrafish

In recent years, the increase in the synthesis of biopesticides for alternative agricultural uses has necessitated the study of their impacts. Among these compounds, several of them are known to exert endocrine-disrupting effects causing deregulation of a variety of physiological functions affecting cell signaling pathways involved in neural cell differentiation leading to developmental neurotoxicity. In this current paper, we thus determined the impact of the biopesticide A6 on zebrafish larvae, which is structurally linked to estrogenic endocrine disruptors. The objective of this study was to define the toxicity of A6, the mechanisms responsible, and to evaluate its effects on the locomotors activity at nanomolar concentrations (0, 0.5, 5, and 50 nM). We show through its blue fluorescence properties that A6 accumulates in different parts of the body as intestine, adipose tissue, muscle, yolk sac and head. We display also that A6 disrupt the development and affects the function of the central nervous system, especially the expression of tyrosine hydroxylase (TH) in dopaminergic neurons. We studied whether A6 disturbs the target genes expression and recorded that it downregulated genes embroiled in TH expression, suggesting that A6's neurotoxic effect may be the result of its binding propinquity to the estrogen receptor.

Activation of the sigma-1 receptor chaperone alleviates symptoms of Wolfram syndrome in preclinical models

The Wolfram syndrome is a rare autosomal recessive disease affecting many organs with life-threatening consequences; currently, no treatment is available. The disease is caused by mutations in the WSF1 gene, coding for the protein wolframin, an endoplasmic reticulum (ER) transmembrane protein involved in contacts between ER and mitochondria termed as mitochondria-associated ER membranes (MAMs). Inherited mutations usually reduce the protein's stability, altering its homeostasis and ultimately reducing ER to mitochondria calcium ion transfer, leading to mitochondrial dysfunction and cell death. In this study, we found that activation of the sigma-1 receptor (S1R), an ER-resident protein involved in calcium ion transfer, could counteract the functional alterations of MAMs due to wolframin deficiency. The S1R agonist PRE-084 restored calcium ion transfer and mitochondrial respiration in vitro, corrected the associated increased autophagy and mitophagy, and was able to alleviate the behavioral symptoms observed in zebrafish and mouse models of the disease. Our findings provide a potential therapeutic strategy for treating Wolfram syndrome by efficiently boosting MAM function using the ligand-operated S1R chaperone. Moreover, such strategy might also be relevant for other degenerative and mitochondrial diseases involving MAM dysfunction.

OUP accepted manuscript

Wolfram syndrome (WS) is a rare genetic disease characterized by diabetes, optic atrophy and deafness. Patients die at 35 years of age, mainly from respiratory failure or dysphagia. Unfortunately, there is no treatment to block the progression of symptoms and there is an urgent need for adequate research models. Here, we report on the phenotypical characterization of two loss-of-function zebrafish mutant lines: wfs1a^C825X and wfs1b^W493X. We observed that wfs1a deficiency altered the size of the ear and the retina of the fish. We also documented a decrease in the expression level of unfolded protein response (UPR) genes in basal condition and in stress condition, i.e. after tunicamycin treatment. Interestingly, both mutants lead to a decrease in their visual function measured behaviorally. These deficits were associated with a decrease in the expression level of UPR genes in basal and stress conditions. Interestingly, basal, ATP-linked and maximal mitochondrial respirations were transiently decreased in the wfs1b mutant. Taken together, these zebrafish lines highlight the critical role of wfs1a and wfs1b in UPR, mitochondrial function and visual physiology. These models will be useful tools to better understand the cellular function of Wfs1 and to develop novel therapeutic approaches for WS.

A rational study of the influence of Mn2+-insertion in Prussian blue nanoparticles on their photothermal properties

We investigated a series of Mn²⁺-Prussian blue (PB) nanoparticles Na_zMn_xFe_1-x[Fe(CN)₆]_1-y□y·nH₂O of similar size, surface state and cubic morphology with various amounts of Mn²⁺ synthesized through a one step self-assembly reaction. We demonstrated by a combined experimental-theoretical approach that during the synthesis, Mn²⁺ substituted Fe³⁺ up to a Mn/Na-Mn-Fe ratio of 32 at% in the PB structure, while for higher amounts, the Mn₂[Fe(CN)₆] analogue is obtained. For comparison, the post-synthetic insertion of Mn2+ in PB nanoparticles was also investigated and completed with Monte-Carlo simulations to probe the plausible adsorption sites. The photothermal conversion efficiency (η) of selected samples was determined and showed a clear dependence on the Mn²⁺amount with a maximum efficiency for a Mn/Na-Mn-Fe ratio of 10 at% associated with a dependence on the nanoparticle concentration. Evaluation of the in vitro photothermal properties of these nanoparticles performed on triple negative human breast adenocarcinoma (MDA-MB-231) cells by using continuous and pulsed laser irradiation confirm their excellent PTT efficiency permitting low dose use.

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

The 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.

Loss of Pde6a Induces Rod Outer Segment Shrinkage and Visual Alterations in pde6aQ70X Mutant Zebrafish, a Relevant Model of Retinal Dystrophy

Retinitis pigmentosa (RP) is one of the most common forms of inherited retinal degeneration with 1/4,000 people being affected. The vision alteration primarily begins with rod photoreceptor degeneration, then the degenerative process continues with cone photoreceptor death. Variants in 71 genes have been linked to RP. One of these genes, PDE6a is responsible for RP43. To date no treatment is available and patients suffer from pronounced visual impairment in early childhood. We used the novel zebrafish pde6a^Q70X mutant, generated by N-ethyl-N-nitrosourea at the European Zebrafish Resource Centre, to better understand how PDE6a loss of function leads to photoreceptor alteration. Interestingly, zebrafish pde6a^Q70X mutants exhibited impaired visual function at 5 dpf as evidenced by the decrease in their visual motor response (VMR) compared to pde6a^WT larvae. This impaired visual function progressed with time and was more severe at 21 dpf. These modifications were associated with an alteration of rod outer segment length at 5 and 21 dpf. In summary, these findings suggest that rod outer segment shrinkage due to Pde6a deficiency begins very early in zebrafish, progresses with time. The zebrafish pde6a^Q70X mutant represents an ideal model of RP to screen relevant active small molecules that will block the progression of the disease.

Ethinylestradiol (EE2) residues from birth control pills impair nervous system development and swimming behavior of zebrafish larvae

The ubiquitous use of ethinylestradiol (EE2), an active constituent of birth control preparations, results in continuous release of this synthetic estrogen to surface waters. Many studies document the untoward effects of EE2 on the endocrine system of aquatic organisms. Effects of environmental EE2 on the nervous system are still poorly documented. We studied effects of pico- to nanomolar concentrations of EE2 on early nervous system development of zebrafish larvae. EE2 disrupted axonal nerve regeneration and hair cell regeneration up to 50%. Gene expression in larval brain tissues showed significantly upregulated expression of target genes, such as estrogen and progesterone receptors, and aromatase B. In contrast, downregulation of the tyrosine hydroxylase, involved in the synthesis of neurotransmitters, occurred concomitant with diminution of proliferating cells. Overall, the size of exposed fish larvae decreased by 25% and their swimming behavior was modified compared to non-treated larvae. EE2 interferes with nervous system development, both centrally and peripherally, with negative effects on regeneration and swimming behavior. Survival of fish and other aquatic species may be at risk in chronically EE2-contaminated environments.

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

Brain-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 neurotoxicity 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 phosphorylation. 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.

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

In previous work [Opt. Lett.44, 2827 (2019)OPLEDP0146-959210.1364/OL.44.002827], 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.

Regenerating islet-derived 1α (REG-1α) protein increases tau phosphorylation in cell and animal models of tauopathies

REG-1α, a secreted protein containing a C-type lectin domain, is expressed in various organs and plays different roles in digestive system cells in physiological and pathological conditions. Like other members of the Reg family, REG-1α is expressed also in the brain where it has different functions. For instance, we previously reported that REG-1α regulates neurite outgrowth and is overexpressed during the very early stages of Alzheimer's disease (AD). However, REG-1α function in neural cells during neural degeneration remains unknown. First, REG-1α and phosphorylated tau expression were assessed in tissue sections from the hippocampus, representing neurofibrillary tangles (NFTs), from patients with AD, and from basal ganglia, representing subcortical NFTs, from patients with progressive supranuclear palsy (PSP). We found an association between REG-1α expression, tau hyperphosphorylation and NFTs in human brain samples from patients with these neurodegenerative diseases. Then, the effects of REG-1α overexpression on tau phosphorylation and axonal morphology were investigated i) in primary cultures of rat neurons that express human tau P301L and ii) in a transgenic zebrafish model of tauopathy that expresses human tau P301L. In the tau P301L cell model, REG-1α overexpression increased tau phosphorylation at the S202/T205 and S396 residues (early and late stages of abnormal phosphorylation, respectively) through the AKT/GSK3-β pathway. This effect was associated with axonal defects both in tau P301L-expressing rat neurons and zebrafish embryos. Our findings suggest a functional role for REG-1α during tauopathy development and progression and, specifically, its involvement in the modification of tau phosphorylation temporal sequence.

Lef1 controls patterning and proliferation in the posterior lateral line system of zebrafish

The embryonic development of the posterior lateral line of zebrafish involves the migration from head to tail of a primordium comprising approximately 100 cells, and the deposition at regular intervals of presumptive mechanosensory organs (neuromasts). Migration depends on the presence of chemokine SDF1 along the pathway, and on the asymmetrical distribution of chemokine receptors CXCR4 and CXCR7 in the primordium. Primordium polarization depends on Wnt signaling in the leading region. Here, we examine the role of a major effector of Wnt signaling, lef1, in this system. We show that, although its inactivation has no overt effect on the expression of cxcr4b and cxcr7b, lef1 contributes to their control. We also show that cell proliferation, which ensures constant primordium size despite successive rounds of cell deposition, is reduced upon lef1 inactivation. Because of this defect, the primordium runs short of cells and vanishes before the line has been completed. We conclude that lef1-mediated Wnt signaling is involved in various aspects of primordium migration, although part of this implication is masked by a high level of developmental redundancy.

CXCR4 and CXCR7 cooperate during tangential migration of facial motoneurons

Migration of facial motoneurons in the zebrafish hindbrain depends on SDF1/CXCL12 signaling. Recent studies demonstrated that SDF1 can bind two chemokine receptors, CXCR4 and CXCR7. Here we explore the expression and function of the cxcr7b gene in zebrafish hindbrain development. By the time cxcr4b-expressing motoneurons migrate from rhombomere (r) r4 to r6, expression of cxcr7b is rapidly restricted to the ventral part of r5. Inactivation of either cxcr7b or cxcr4b impairs motoneuron migration, with however different phenotypes. Facial motoneurons preferentially accumulate in r5 in cxcr7b morphant embryos, while they are distributed between r4, r5 and r6 in cxcr4b morphants. Simultaneous inactivation of both receptors leads to yet a third phenotype, with motoneurons mostly distributed between r4 and r5. The latter phenotype resembles that of sdf1a morphant embryos. Double inactivation of sdf1a and cxcr7b indeed did not lead to a complete arrest of migration but rather to a partial rescue of r5 arrest of motoneuron migration. This result is in accordance with the functional hypothesis that SDF1 might interact with CXCR7 and that they have an antagonistic effect within r5. The ectopic expression of a truncated CXCR7 receptor leads to a motoneuron migration defect. Altogether, we show that CXCR7 is required, for proper tangential migration of facial motoneurons, by determining a permissive migration pathway through r5.

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.

Pattern formation in the lateral line of zebrafish

The lateral line of fish and amphibians is a sensory system that comprises a number of individual sense organs, the neuromasts, arranged in a defined pattern on the surface of the body. A conspicuous part of the system is a line of organs that extends along each flank (and which gave the system its name). At the end of zebrafish embryogenesis, this line comprises 7-8 neuromasts regularly spaced between the ear and the tip of the tail. The neuromasts are deposited by a migrating primordium that originates from the otic region. Here, we follow the development of this pattern and show that heterogeneities within the migrating primordium prefigure neuromast formation.