Neurogenesis in zebrafish - from embryo to adult

Telencephalic stab wound injury induces regenerative angiogenesis and neurogenesis in zebrafish: unveiling the role of vascular endothelial growth factor signaling and microglia

JOURNAL/nrgr/04.03/01300535-202510000-00025/figure1/v/2024-11-26T163120Z/r/image-tiff After brain damage, regenerative angiogenesis and neurogenesis have been shown to occur simultaneously in mammals, suggesting a close link between these processes. However, the mechanisms by which these processes interact are not well understood. In this work, we aimed to study the correlation between angiogenesis and neurogenesis after a telencephalic stab wound injury. To this end, we used zebrafish as a relevant model of neuroplasticity and brain repair mechanisms. First, using the Tg( fli1:EGFP × mpeg1.1:mCherry ) zebrafish line, which enables visualization of blood vessels and microglia respectively, we analyzed regenerative angiogenesis from 1 to 21 days post-lesion. In parallel, we monitored brain cell proliferation in neurogenic niches localized in the ventricular zone by using immunohistochemistry. We found that after brain damage, the blood vessel area and width as well as expression of the fli1 transgene and vascular endothelial growth factor ( vegfaa and vegfbb ) were increased. At the same time, neural stem cell proliferation was also increased, peaking between 3 and 5 days post-lesion in a manner similar to angiogenesis, along with the recruitment of microglia. Then, through pharmacological manipulation by injecting an anti-angiogenic drug (Tivozanib) or Vegf at the lesion site, we demonstrated that blocking or activating Vegf signaling modulated both angiogenic and neurogenic processes, as well as microglial recruitment. Finally, we showed that inhibition of microglia by clodronate-containing liposome injection or dexamethasone treatment impairs regenerative neurogenesis, as previously described, as well as injury-induced angiogenesis. In conclusion, we have described regenerative angiogenesis in zebrafish for the first time and have highlighted the role of inflammation in this process. In addition, we have shown that both angiogenesis and neurogenesis are involved in brain repair and that microglia and inflammation-dependent mechanisms activated by Vegf signaling are important contributors to these processes. This study paves the way for a better understanding of the effect of Vegf on microglia and for studies aimed at promoting angiogenesis to improve brain plasticity after brain injury.

Lipidomics Atlas Tracks Alterations Associated with Deltamethrin-Induced Developmental Neurotoxicity in Embryonic Zebrafish

Deltamethrin (DM) is a widely used pyrethroid pesticide associated with childhood neurodevelopmental disorders. However, the specific impact of DM exposure during distinct early life stages remains unclear. Here, zebrafish embryos were exposed to DM at different stages: before (10-16 hpf), at the onset of (16-24 hpf), at the peak of (24-36 hpf) hypothalamic neurogenesis, and continuously from 10 to 120 hpf (subchronic exposure), using different dosages (1, 100, and 250 nM). Exposure to middle/high-dose DM at 24-36 and 10-120 hpf significantly reduced zebrafish locomotor activities and increased apoptotic cells in the spinal cord. As a pivotal factor in central nervous system disorder progression, altered lipid metabolism was investigated using nontargeted lipidomic analysis. DM exposure at 10-16 and 24-36 hpf led to the most significant lipidome reprogramming. Despite exhibiting a dose-dependent trend, even low-dose DM changed the lipidome. Cer 40:2;2 and PG 44:12 showed potential in identifying DM exposure effects. Significant changes in sphingolipid, cardiolipin, phosphatidylglycerol, and glycerolipid pathways were linked to DM-induced developmental neurotoxicity, indicating impaired membrane function, mitochondrial damage, and disrupted energy metabolism. Our study sheds new light on assessing early neurodevelopmental disturbances and identifying intervention targets, emphasizing sensitivity to DM during the critical early phase of neurodevelopment.

CFTR acts as a potential therapeutic target for attention deficit-hyperactivity disorder

The prevalence of attention deficit-hyperactivity disorder (ADHD) symptoms among individuals with cystic fibrosis (CF) is significantly elevated compared to the general population. Given that the cystic fibrosis transmembrane conductance regulator (CFTR) is the causative gene for cystic fibrosis, this raises the possibility of CFTR playing a crucial role in ADHD. In our study, three heterozygous missense variants (p.E217G, p.F316L, and p.T1220I) were detected in the CFTR gene, which co-segregate with ADHD in two consanguineous families, impacting a total of six family members. Through the utilization of a zebrafish model, it was observed that the cftr knockout line exhibited behaviors akin to hyperactivity, impulsivity, and attention deficits, mirroring the symptoms seen in human ADHD patients. Single-cell RNA sequencing performed on 7 dpf larvae revealed clusters of neuron cells that exhibited sensitivity to cftr, particularly noting a reduction in the number of dopaminergic neuron cells within the cftr mutant fish. Additionally, bulk RNA sequencing and proteomic analysis conducted during the early gastrulation stage demonstrated abnormal expression levels of nervous system genes. Notably, we attempted to employ CFTR modulators Lumacaftor (VX-809) and Ivacaftor (VX-770) to ameliorate the ADHD zebrafish model (generated via per1b mutant), and it was found that enhanced CFTR activity could mitigate ADHD-like behaviors. In summary, our findings shed light on the potential involvement of CFTR in the pathogenesis of ADHD and pave the way for exploring novel diagnostic approaches and therapeutic strategies for ADHD by targeting CFTR.

Life History-Dependent Brain Transcriptomic Signatures in Nothobranchids: Insights into Aging, Neurogenesis, and Life History Evolution

The African turquoise killifish Nothobranchius furzeri is a powerful model organism in aging research. Within the family Nothobranchiidae, a wide range of lifespan is observed in annual, semi-annual, and non-annual life histories. In this study, we examined the brain transcriptomic signatures of adult nothobranchids across life history variations. Our results show that the brain gene expression profiles exhibit strong life history signatures compared to the liver tissue. Semi-annual Fundulopanchax species shows upregulation in cell division and mitosis compared to non-annual Aphyosemion species. We identified genes related to neurogenesis such as DNMT3A, SOX2, and FGF10 that show downregulation in the short-lived annual species compared to other life histories. The Notch signaling pathway is enriched in the non-annual species suggesting the importance of this pathway in longer-lived killifish. Our study demonstrates that other non-model nothobranchids can be used as comparative species to N .  furzeri in the study of aging, neurogenesis, and life history.

Definition of the characteristic neurogenesis pattern in the neural plate by the Hes1 orthologue gene, her6, during early zebrafish development

During vertebrate embryonic development, a distinctive, spotty neurogenesis pattern emerges in the early neural plate, which represents proneural clusters. The determination of this pattern depends on the interaction between proneural genes and bHLH-O-type transcription factor (TF) genes, Hes/her, which suppress neurogenesis. In this study, we focused on the mouse Hes1 orthologue, her6, to understand the mechanism that controls neurodevelopmental patterns in the developing brain in zebrafish (Danio rerio). We first assessed the expression pattern of her6 in the neural plate, observing that it is consistently expressed in the entire forebrain throughout somitogenesis, including her9 expression within it. Meanwhile, the expression patterns of her6 changed dynamically in the hindbrain, in contrast to the Notch-independent her genes. The expression pattern was not significantly affected by forced NICD expression and DAPT treatment at the bud stage, showing that her6 expression is Notch-independent in the neural plate at this stage. To analyze the roles of her6, we disrupted her6 using the CRISPR/Cas9 method. The mutants thus obtained showed a deformed midbrain-hindbrain region and failed to grow to adulthood. At the bud stage, ectopic expression of neurogenesis-related genes was observed in her6 mutants in specific regions of the neural plate, where neurogenesis does not occur and which are considered neural progenitor pools (NPPs) in wild-type embryos. Of note, no other Notch-independent her genes are known to be expressed in these NPP regions. In contrast, the expression of regionalization genes in the forebrain and hindbrain was not affected in her6 mutants. These findings suggest that her6 defines the primary neurogenesis pattern in the neural plate, together with other Notch-independent her genes.

A multi-omics approach reveals impaired lipid metabolism and oxidative stress in a zebrafish model of Alexander disease

Alexander disease (AxD) is a rare leukodystrophy caused by heterozygous mutations in the GFAP gene. To date, several in vitro and in vivo models have been generated in an attempt to unravel the main mechanisms underlying this complex disease. However, none of these models is suitable for investigating the global dysregulation caused by AxD. To address this shortcoming, we have generated a stable transgenic zebrafish line (zAxD) carrying the human GFAP p.R239C mutation, which is associated with severe phenotypes of AxD type I patients. We then performed transcriptomics and proteomics analyses on the whole larvae of our zAxD model, confirming the involvement of several pathways such as the immune system response and inflammation, oxidative stress, extracellular matrix, lipoxidation and lipid metabolism, which were previously reported in more limited omic studies. Interestingly, new pathways emerged as well, including tyrosine and butanoate metabolic processes. Biochemical assays confirmed alterations in cell respiration and lipid metabolism as well as elevated oxidative stress. These findings confirm the reliability of the zAxD model to apply a whole-organism approach to investigate the molecular basis of the disease.

Chronic Exposure of Zebrafish to Iron and Aluminum: Evaluation of Reversal and Generational Transposition of Behavioral, Histopathological, and Genotoxic Changes

This study aimed to report the effects of chronic exposure of zebrafish exposed to environmentally relevant concentrations of 0.5, 2.4, and 5.0 mg L-1 iron (Fe) and 0.2, 0.4, and 2.0 mg L-1 aluminum (Al). We also evaluated the reversal and generational transposition (F1) of possible histopathological, behavioral, and genotoxic changes in the species. Locomotion changes that may have been caused by the increase in the number of apoptotic cells and in the telencephalic mitochondrial activity were observed especially after the 30 days exposure to Al and persisted after recovery (30 days). We also observed histopathological changes, such as an increase in the number of intestinal goblet cells, even after the recovery period in these animals. Our results also showed that the Fe concentrations used were insufficient to cause genotoxicity, behavioral and intestinal epithelium changes. The adult offspring (F1) of animals exposed to Al showed changes in locomotion and in the amount of goblet cells, demonstrating that even in low concentrations this pollutant can harm subsequent generations in the aquatic biota. Animals demonstrate, in general, greater tolerance to Fe which may be related to the physiological demand of this metal by the body. Even so, all concentrations of both metals that caused some change in the species represent Brazilian environmental occurrences or Brazilian legislation. It highlights the need for updating the guidelines and constant monitoring of aquatic environments, since even in the face of a hypothetical decontamination of the environment, some changes could persist and affect different trophic levels.

tubg1 Somatic Mutants Show Tubulinopathy-Associated Neurodevelopmental Phenotypes in a Zebrafish Model

Development of the multilayered cerebral cortex relies on precise orchestration of neurogenesis, neuronal migration, and differentiation, processes tightly regulated by microtubule dynamics. Mutations in tubulin superfamily genes have been associated with tubulinopathies, encompassing a spectrum of cortical malformations including microcephaly and lissencephaly. Here, we focus on γ-tubulin, a pivotal regulator of microtubule nucleation encoded by TUBG1. We investigate its role in brain development using a zebrafish model with somatic tubg1 mutation, recapitulating features of TUBG1-associated tubulinopathies in patients and mouse disease models. We demonstrate that γ-tubulin deficiency disrupts neurogenesis and brain development, mirroring microcephaly phenotypes. Furthermore, we uncover a novel potential regulatory link between γ-tubulin and canonical Wnt/β-catenin signaling, with γ-tubulin deficiency impairing Wnt activity. Our findings provide insights into the pathogenesis of cortical defects and suggest that γ-tubulin could be a potential target for further research in neurodevelopmental disorders, although challenges such as mode of action, specificity, and potential side effects must be addressed.

Developmental and neurotoxic effects of dimethyl phthalate on zebrafish embryos and larvae

Dimethyl phthalate (DMP) has been extensively utilized as a plasticizer on a global scale for many years. Its presence in the environment and its harmful effects on living organisms have raised concerns. This study aimed to examine its potential developmental neurotoxicity by utilizing zebrafish as a model. Zebrafish embryos were exposed to different concentrations of DMP (5-100 mg/L) from 4 to 120 h post-fertilization (hpf). The survival, hatching, and malformation rates were recorded for each group. Behavioral analysis was conducted on zebrafish larvae, and transgenic zebrafish Tg(elavl3:EGFP) were used to assess the impact of DMP on neuronal cells. The mRNA levels of key neurological marker genes were evaluated at 96 hpf of DMP exposure. The study revealed that exposure to DMP resulted in decreased survival and hatching rates in zebrafish. Embryos treated with 50 mg/L of DMP exhibited lower average survival rates (72.78-78.33%) between 24-96 hpf, while treatment with 25-50 mg/L of DMP resulted in reduced hatching rates (39.44% and 2.22%, respectively) at 48 hpf compared to the control group. Moreover, exposure to 25-50 mg/L of DMP caused an increase in malformations, such as tail curvature, spinal curvature, yolk sac edema and pericardial edema. Interestingly, at 24 hpf, DMP also resulted in an increase in spontaneous tail coiling in zebrafish embryos, as well as a decrease in their swimming distance at 120 hpf. Furthermore, treatment with 50 mg/L of DMP led to a decrease in the fluorescence intensity of transgenic zebrafish Tg(elavl3: EGFP). RT-qPCR analysis showed a significant down-regulation of marker genes (gap43, mbp, α1-tubulin, syn2a) associated with nervous system function in DMP-treated zebrafish. Overall, these findings offer a thorough understanding of the mechanisms underlying the neurotoxicity caused by DMP, highlighting the risk of DMP on developmental and neurotoxic effects in zebrafish. Therefore, strict supervision of DMP use and release is essential to safeguard ecological and aquatic organisms.

Small Fish, Big Answers: Zebrafish and the Molecular Drivers of Metastasis

Cancer metastasis is a leading cause of cancer-related deaths and represents one of the most challenging processes to study due to its complexity and dynamic nature. Zebrafish (Danio rerio) have become an invaluable model in metastasis research, offering unique advantages such as optical transparency, rapid development, and the ability to visualize tumor interactions with the microenvironment in real time. This review explores how zebrafish models have elucidated the critical steps of metastasis, including tumor invasion, vascular remodeling, and immune evasion, while also serving as platforms for drug testing and personalized medicine. Advances such as patient-derived xenografts and innovative genetic tools have further established zebrafish as a cornerstone in cancer research, particularly in understanding the molecular drivers of metastasis and identifying therapeutic targets. By bridging the experimental findings with clinical relevance, zebrafish continue transforming our understanding of cancer biology and therapy.

Barcoding Notch signaling in the developing brain

Developmental signaling inputs are fundamental for shaping cell fates and behavior. However, traditional fluorescent-based signaling reporters have limitations in scalability and molecular resolution of cell types. We present SABER-seq, a CRISPR-Cas molecular recorder that stores transient developmental signaling cues as permanent mutations in cellular genomes for deconstruction at later stages via single-cell transcriptomics. We applied SABER-seq to record Notch signaling in developing zebrafish brains. SABER-seq has two components: a signaling sensor and a barcode recorder. The sensor activates Cas9 in a Notch-dependent manner with inducible control, while the recorder obtains mutations in ancestral cells where Notch is active. We combine SABER-seq with an expanded juvenile brain atlas to identify cell types derived from Notch-active founders. Our data reveal rare examples where differential Notch activities in ancestral progenitors are detected in terminally differentiated neuronal subtypes. SABER-seq is a novel platform for rapid, scalable and high-resolution mapping of signaling activity during development.

A zebrafish-based in vivo model of Zika virus infection unveils alterations of the glutamatergic neuronal development and NS4A as a key viral determinant of neuropathogenesis

Infection of pregnant women by Zika virus (ZIKV) is associated with severe neurodevelopmental defects in newborns through poorly defined mechanisms. Here, we established a zebrafish in vivo model of ZIKV infection to circumvent limitations of existing mammalian models. Leveraging the unique tractability of this system, we gained unprecedented access to the ZIKV-infected brain at early developmental stages. The infection of zebrafish larvae with ZIKV phenocopied the disease in mammals including a reduced head area and neural progenitor cells (NPC) infection and depletion. Moreover, transcriptomic analyses of NPCs isolated from ZIKV-infected embryos revealed a distinct dysregulation of genes involved in survival and neuronal differentiation, including downregulation of the expression of the glutamate transporter vglut1, resulting in an altered glutamatergic network in the brain. Mechanistically, ectopic expression of ZIKV protein NS4A in the larvae recapitulated the morphological defects observed in infected animals, identifying NS4A as a key determinant of neurovirulence and a promising antiviral target for developing therapies.

Developmental exposure of zebrafish to saxitoxin causes altered expression of genes associated with axonal growth

Saxitoxin (STX) is a potent neurotoxin naturally produced by dinoflagellates and cyanobacteria. STX inhibits voltage-gated sodium channels (VGSCs), affecting the propagation of action potentials. Consumption of seafood contaminated with STX is responsible for paralytic shellfish poisoning (PSP). Humans are among the species most sensitive to PSP; neurological symptoms of exposure range from tingling of the extremities to severe paralysis. The objective of this study was to determine the effects of STX exposure on developmental processes during early embryogenesis. This study was designed to test the hypothesis that early developmental exposure to STX would disrupt key processes, particularly those related to neural development. Zebrafish embryos were exposed to STX (24 or 48 pg) or vehicle (0.3 mM HCl) at 6 h post fertilization (hpf) via microinjection. There was no overt toxicity but starting at 36 hpf there was a temporary lack of pigmentation in STX-injected embryos, which resolved by 72 hpf. Using high performance liquid chromatography, we found that STX was retained in embryos up to 72 hpf in a dose-dependent manner. Temporal transcriptional profiling of embryos exposed to 48 pg STX per embryo revealed no differentially expressed genes (DEGs) at 24 hpf, but at 36 and 48 hpf, there were 3547 and 3356 DEGs, respectively. KEGG pathway analysis revealed significant enrichment of genes related to focal adhesion, adherens junction and regulation of actin cytoskeleton, suggesting that cell-cell and cell-extracellular matrix interactions were affected by STX. Genes affected are critical for axonal growth and the development of functional neural networks. We confirmed these findings by visualizing axonal defects in transgenic zebrafish with fluorescently labeled sensory neurons. In addition, our gene expression results suggest that STX exposure affects both canonical and noncanonical functions of VGSCs. Given the fundamental role of VGSCs in both physiology and development, these findings offer valuable insights into effects of exposure to neurotoxins.

Socially induced plasticity of the posterior tuberculum and motor behavior in zebrafish (Danio rerio)

Social dominance is prevalent throughout the animal kingdom. It facilitates the stabilization of social relationships and allows animals to divide resources according to social rank. Zebrafish form stable dominance relationships that consist of dominants and subordinates. Although social status-dependent differences in behavior must arise as a result of neural plasticity, mechanisms by which neural circuits are reconfigured to cope with social dominance are poorly described. Here, we describe how the posterior tuberculum nucleus (PTN), which integrates sensory social information to modulate spinal motor circuits, is morphologically and functionally influenced by social status. We combined non-invasive behavioral monitoring of motor activity (startle escape and swim) and histological approaches to investigate how social dominance affects the morphological structure, axosomatic synaptic connectivity and functional activity of the PTN in relation to changes in motor behavior. We show that dopaminergic cell number significantly increases in dominants compared with subordinates, while PTN synaptic interconnectivity, demonstrated with PSD-95 expression, is higher in subordinates than in dominants. Secondly, these socially induced morphological differences emerge after 1 week of dominance formation and correlate with differences in cellular activities illustrated with higher phosphor-S6 ribosomal protein expression in dominants compared with subordinates. Thirdly, these morphological differences are reversible as the social environment evolves and correlate with adaptations in startle escape and swim behaviors. Our results provide new insights into the neural bases of social behavior that may be applicable to other social species with similar structural and functional organization.

Concussion leads to opposing sensorimotor effects of habituation deficit and fatigue in zebrafish larvae

Concussion, or mild traumatic brain injury, is caused by sudden mechanical forces impacting the brain either directly or through inertial loading. This can lead to physical, behavioural and cognitive impairments. Despite concussion being a significant health issue, our understanding of the relationship between initial impact force and the subsequent neurological consequences is not well understood. Previously, we established a model of concussion in zebrafish larvae. Here, we further investigate concussions of varying severities in zebrafish larvae using linear deceleration. Using an acoustic assay to monitor the larval sensorimotor behaviour, we found that different parameters of the resulting escape behaviour are modulated by the impact force of the preceding concussive insult. To investigate the relative contributions of habituation performance and fatigue on the escape response behaviour, we constructed a neurocomputational model. Our findings suggest that a concussive impact initially affects habituation performance at first and, as the impact force increases, fatigue is induced. Fatigue then alters the escape response behaviour in an opposing manner.

Generating neurons in the embryonic and adult brain: compared principles and mechanisms

Neurogenesis is a lifelong process, generating neurons in the right amount, time and place and with the correct identity to permit the growth, function, plasticity and repair of the nervous system, notably the brain. Neurogenesis originates from neural progenitor cells (NPs), endowed with the capacity to divide, renew to maintain the progenitor population, or commit to engage in the neurogenesis process. In the adult brain, these progenitors are classically called neural stem cells (NSCs). We review here the commonalities and differences between NPs and NSCs, in their cellular and molecular attributes but also in their potential, regulators and lineage, in the embryonic and adult brains. Our comparison is based on the two most studied model systems, namely the telencephalon of the zebrafish and mouse. We also discuss how the population of embryonic NPs gives rise to adult NSCs, and outstanding questions pertaining to this transition.

Neural Stem Cell Regulation in Zebrafish

Neural stem cells (NSCs) are progenitor cell populations generating glial cells and neurons and endowed with long-lasting self-renewal and differentiation potential. While some neural progenitors (NPs) in the embryonic nervous system are also long-lived and match this definition, the term NSC classically refers to such progenitor types in the adult. With the discovery of extensive NSC populations in the adult brain of Danio rerio (zebrafish) and of their high neurogenic activity, including for neuronal regeneration, this model organism has become a powerful tool to characterize and mechanistically dissect NSC properties. On these bases, this article will consider NSCs in the adult zebrafish brain, with a focus on its most extensively characterized domain, the telencephalon (notably its dorsal part, the pallium). Whenever necessary, we will also refer to other brain subdivisions, embryonic processes, and the mouse adult brain, whether for comparative purposes or because more information is available in these other systems.

A reproducible method to study traumatic injury-induced zebrafish brain regeneration

Traumatic brain injury (TBI) can be caused by a sudden blow or jolt to the head, causing irreversible brain damage leading to cellular and functional loss. Mammals cannot repair such damage, which may increase the risk of progressive neurodegeneration. Unlike mammals, lower vertebrates such as zebrafish have the astounding capability to regenerate their brains. A model system would be of great value to study zebrafish brain regeneration. Here, we describe a physical method to induce traumatic injury in the zebrafish brain and outline a pipeline to utilize this model system to explore various aspects of brain regeneration. This will significantly advance the fields of regenerative biology and neuroscience. The method includes inducing TBI and validating this through histological assays, immunohistochemistry, and gene expression analysis. By using this model system, researchers will be able to gain valuable insights into the cellular and molecular mechanisms underlying brain regeneration. Understanding these mechanisms could lead to the identification of potential strategies to address neurodegenerative conditions in higher vertebrates.

Embryonic Zebrafish as a Model for Investigating the Interaction between Environmental Pollutants and Neurodegenerative Disorders

Environmental pollutants have been linked to neurotoxicity and are proposed to contribute to neurodegenerative disorders. The zebrafish model provides a high-throughput platform for large-scale chemical screening and toxicity assessment and is widely accepted as an important animal model for the investigation of neurodegenerative disorders. Although recent studies explore the roles of environmental pollutants in neurodegenerative disorders in zebrafish models, current knowledge of the mechanisms of environmentally induced neurodegenerative disorders is relatively complex and overlapping. This review primarily discusses utilizing embryonic zebrafish as the model to investigate environmental pollutants-related neurodegenerative disease. We also review current applicable approaches and important biomarkers to unravel the underlying mechanism of environmentally related neurodegenerative disorders. We found embryonic zebrafish to be a powerful tool that provides a platform for evaluating neurotoxicity triggered by environmentally relevant concentrations of neurotoxic compounds. Additionally, using variable approaches to assess neurotoxicity in the embryonic zebrafish allows researchers to have insights into the complex interaction between environmental pollutants and neurodegenerative disorders and, ultimately, an understanding of the underlying mechanisms related to environmental toxicants.

Diving deep: zebrafish models in motor neuron degeneration research

In the dynamic landscape of biomedical science, the pursuit of effective treatments for motor neuron disorders like hereditary spastic paraplegia (HSP), amyotrophic lateral sclerosis (ALS), and spinal muscular atrophy (SMA) remains a key priority. Central to this endeavor is the development of robust animal models, with the zebrafish emerging as a prime candidate. Exhibiting embryonic transparency, a swift life cycle, and significant genetic and neuroanatomical congruencies with humans, zebrafish offer substantial potential for research. Despite the difference in locomotion-zebrafish undulate while humans use limbs, the zebrafish presents relevant phenotypic parallels to human motor control disorders, providing valuable insights into neurodegenerative diseases. This review explores the zebrafish's inherent traits and how they facilitate profound insights into the complex behavioral and cellular phenotypes associated with these disorders. Furthermore, we examine recent advancements in high-throughput drug screening using the zebrafish model, a promising avenue for identifying therapeutically potent compounds.

Altered Morpho-Functional Features of Neurogenesis in Zebrafish Embryos Exposed to Non-Combustion-Derived Magnetite

Neurogenesis is the process by which new brain cells are formed. This crucial event emerges during embryonic life and proceeds in adulthood, and it could be influenced by environmental pollution. Non-combustion-derived magnetite represents a portion of the coarse particulate matter (PM) contributing to air and water pollution in urban settings. Studies on humans have reported that magnetite and other iron oxides have significant damaging effects at a central level, where these particles accumulate and promote oxidative stress. Similarly, magnetite nanoparticles can cross the placenta and damage the embryo brain during development, but the impact on neurogenesis is still unknown. Furthermore, an abnormal Fe cation concentration in cells and tissues might promote reactive oxygen species (ROS) generation and has been associated with multiple neurodegenerative conditions. In the present study, we used zebrafish as an in vivo system to analyze the specific effects of magnetite on embryonic neurogenesis. First, we characterized magnetite using mineralogical and spectroscopic analyses. Embryos treated with magnetite at sub-lethal concentrations showed a dose-response increase in ROS in the brain, which was accompanied by a massive decrease in antioxidant genes (sod2, cat, gsr, and nrf2). In addition, a higher number of apoptotic cells was observed in embryos treated with magnetite. Next, interestingly, embryos exposed to magnetite displayed a decrease in neural staminal progenitors (nestin, sox2, and pcna markers) and a neuronal marker (elavl3). Finally, we observed significative increases in apoeb (specific microglia marker) and interleukin-1b (il1b), confirming a status of inflammation in the brain embryos treated with magnetite. Our study represents the very first in vivo evidence concerning the effects of magnetite on brain development.

Cell coupling compensates for changes in single-cell Her6 dynamics and provides phenotypic robustness

This paper investigates the effect of altering the protein expression dynamics of the bHLH transcription factor Her6 at the single-cell level in the embryonic zebrafish telencephalon. Using a homozygote endogenous Her6:Venus reporter and 4D single-cell tracking, we show that Her6 oscillates in neural telencephalic progenitors and that the fusion of protein destabilisation (PEST) domain alters its expression dynamics, causing most cells to downregulate Her6 prematurely. However, counterintuitively, oscillatory cells increase, with some expressing Her6 at high levels, resulting in increased heterogeneity of Her6 expression in the population. These tissue-level changes appear to be an emergent property of coupling between single-cells, as revealed by experimentally disrupting Notch signalling and by computationally modelling alterations in Her6 protein stability. Despite the profound differences in the single-cell Her6 dynamics, the size of the telencephalon is only transiently altered and differentiation markers do not exhibit significant differences early on; however, a small increase is observed at later developmental stages. Our study suggests that cell coupling provides a compensation strategy, whereby an almost normal phenotype is maintained even though single-cell gene expression dynamics are abnormal, granting phenotypic robustness.

Barcoding Notch signaling in the developing brain

Developmental signaling inputs are fundamental for shaping cell fates and behavior. However, traditional fluorescent-based signaling reporters have limitations in scalability and molecular resolution of cell types. We present SABER-seq, a CRISPR-Cas molecular recorder that stores transient developmental signaling cues as permanent mutations in cellular genomes for deconstruction at later stages via single-cell transcriptomics. We applied SABER-seq to record Notch signaling in developing zebrafish brains. SABER-seq has two components: a signaling sensor and a barcode recorder. The sensor activates Cas9 in a Notch-dependent manner with inducible control while the recorder accumulates mutations that represent Notch activity in founder cells. We combine SABER-seq with an expanded juvenile brain atlas to define cell types whose fates are determined downstream of Notch signaling. We identified examples wherein Notch signaling may have differential impact on terminal cell fates. SABER-seq is a novel platform for rapid, scalable and high-resolution mapping of signaling activity during development.

New approach methods to assess developmental and adult neurotoxicity for regulatory use: a PARC work package 5 project

In the European regulatory context, rodent in vivo studies are the predominant source of neurotoxicity information. Although they form a cornerstone of neurotoxicological assessments, they are costly and the topic of ethical debate. While the public expects chemicals and products to be safe for the developing and mature nervous systems, considerable numbers of chemicals in commerce have not, or only to a limited extent, been assessed for their potential to cause neurotoxicity. As such, there is a societal push toward the replacement of animal models with in vitro or alternative methods. New approach methods (NAMs) can contribute to the regulatory knowledge base, increase chemical safety, and modernize chemical hazard and risk assessment. Provided they reach an acceptable level of regulatory relevance and reliability, NAMs may be considered as replacements for specific in vivo studies. The European Partnership for the Assessment of Risks from Chemicals (PARC) addresses challenges to the development and implementation of NAMs in chemical risk assessment. In collaboration with regulatory agencies, Project 5.2.1e (Neurotoxicity) aims to develop and evaluate NAMs for developmental neurotoxicity (DNT) and adult neurotoxicity (ANT) and to understand the applicability domain of specific NAMs for the detection of endocrine disruption and epigenetic perturbation. To speed up assay time and reduce costs, we identify early indicators of later-onset effects. Ultimately, we will assemble second-generation developmental neurotoxicity and first-generation adult neurotoxicity test batteries, both of which aim to provide regulatory hazard and risk assessors and industry stakeholders with robust, speedy, lower-cost, and informative next-generation hazard and risk assessment tools.

Dolutegravir and Folic Acid Interaction during Neural System Development in Zebrafish Embryos

Dolutegravir (DTG) is one of the most prescribed antiretroviral drugs for treating people with HIV infection, including women of child-bearing potential or pregnant. Nonetheless, neuropsychiatric symptoms are frequently reported. Early reports suggested that, probably in relation to folic acid (FA) shortage, DTG may induce neural tube defects in infants born to women taking the drug during pregnancy. Subsequent reports did not definitively confirm these findings. Recent studies in animal models have highlighted the association between DTG exposure in utero and congenital anomalies, and an increased risk of neurologic abnormalities in children exposed during in utero life has been reported. Underlying mechanisms for DTG-related neurologic symptoms and congenital anomalies are not fully understood. We aimed to deepen our knowledge on the neurodevelopmental effects of DTG exposure and further explore the protective role of FA by the use of zebrafish embryos. We treated embryos at 4 and up to 144 h post fertilization (hpf) with a subtherapeutic DTG concentration (1 μM) and observed the disruption of the anterior-posterior axis and several morphological malformations in the developing brain that were both prevented by pre-exposure (2 hpf) and rescued by post-exposure (10 hpf) with FA. By whole-mount in situ hybridization with riboprobes for genes that are crucial during the early phases of neurodevelopment (ntl, pax2a, ngn1, neurod1) and by in vivo visualization of the transgenic Tg(ngn1:EGFP) zebrafish line, we found that DTG induced severe neurodevelopmental defects over time in most regions of the nervous system (notochord, midbrain-hindbrain boundary, eye, forebrain, midbrain, hindbrain, spinal cord) that were mostly but not completely rescued by FA supplementation. Of note, we observed the disruption of ngn1 expression in the dopaminergic regions of the developing forebrain, spinal cord neurons and spinal motor neuron projections, with the depletion of the tyrosine hydroxylase (TH)+ dopaminergic neurons of the dorsal diencephalon and the strong reduction in larvae locomotion. Our study further supports previous evidence that DTG can interfere with FA pathways in the developing brain but also provides new insights regarding the mechanisms involved in the increased risk of DTG-associated fetal neurodevelopmental defects and adverse neurologic outcomes in in utero exposed children, suggesting the impairment of dopaminergic pathways.

Shedding a Light on Dark Genes: A Comparative Expression Study of PRR12 Orthologues during Zebrafish Development

Haploinsufficiency of the PRR12 gene is implicated in a human neuro-ocular syndrome. Although identified as a nuclear protein highly expressed in the embryonic mouse brain, PRR12 molecular function remains elusive. This study explores the spatio-temporal expression of zebrafish PRR12 co-orthologs, prr12a and prr12b, as a first step to elucidate their function. In silico analysis reveals high evolutionary conservation in the DNA-interacting domains for both orthologs, with significant syntenic conservation observed for the prr12b locus. In situ hybridization and RT-qPCR analyses on zebrafish embryos and larvae reveal distinct expression patterns: prr12a is expressed early in zygotic development, mainly in the central nervous system, while prr12b expression initiates during gastrulation, localizing later to dopaminergic telencephalic and diencephalic cell clusters. Both transcripts are enriched in the ganglion cell and inner neural layers of the 72 hpf retina, with prr12b widely distributed in the ciliary marginal zone. In the adult brain, prr12a and prr12b are found in the cerebellum, amygdala and ventral telencephalon, which represent the main areas affected in autistic patients. Overall, this study suggests PRR12's potential involvement in eye and brain development, laying the groundwork for further investigations into PRR12-related neurobehavioral disorders.

Elongation of the developing spinal cord is driven by Oct4-type transcription factor-mediated regulation of retinoic acid signaling in zebrafish embryos

BACKGROUND

Elongation of the spinal cord is dependent on neural development from neuromesodermal progenitors in the tail bud. We previously showed the involvement of the Oct4-type gene, pou5f3, in this process in zebrafish mainly by dominant-interference gene induction, but, to compensate for the limitation of this transgene approach, mutant analysis was indispensable. pou5f3 involvement in the signaling pathways was another unsolved question.

RESULTS

We examined the phenotypes of pou5f3 mutants and the effects of Pou5f3 activation by the tamoxifen-ERT2 system in the posterior neural tube, together confirming the involvement of pou5f3. The reporter assays using P19 cells implicated tail bud-related transcription factors in pou5f3 expression. Regulation of tail bud development by retinoic acid (RA) signaling was confirmed by treatment of embryos with RA and the synthesis inhibitor, and in vitro reporter assays further showed that RA signaling regulated pou5f3 expression. Importantly, the expression of the RA degradation enzyme gene, cyp26a1, was down-regulated in embryos with disrupted pou5f3 activity.

CONCLUSIONS

The involvement of pou5f3 in spinal cord extension was supported by using mutants and the gain-of-function approach. Our findings further suggest that pou5f3 regulates the RA level, contributing to neurogenesis in the posterior neural tube.

Adult Neurogenesis of Teleost Fish Determines High Neuronal Plasticity and Regeneration

Studying the properties of neural stem progenitor cells (NSPCs) in a fish model will provide new information about the organization of neurogenic niches containing embryonic and adult neural stem cells, reflecting their development, origin cell lines and proliferative dynamics. Currently, the molecular signatures of these populations in homeostasis and repair in the vertebrate forebrain are being intensively studied. Outside the telencephalon, the regenerative plasticity of NSPCs and their biological significance have not yet been practically studied. The impressive capacity of juvenile salmon to regenerate brain suggests that most NSPCs are likely multipotent, as they are capable of replacing virtually all cell lineages lost during injury, including neuroepithelial cells, radial glia, oligodendrocytes, and neurons. However, the unique regenerative profile of individual cell phenotypes in the diverse niches of brain stem cells remains unclear. Various types of neuronal precursors, as previously shown, are contained in sufficient numbers in different parts of the brain in juvenile Pacific salmon. This review article aims to provide an update on NSPCs in the brain of common models of zebrafish and other fish species, including Pacific salmon, and the involvement of these cells in homeostatic brain growth as well as reparative processes during the postraumatic period. Additionally, new data are presented on the participation of astrocytic glia in the functioning of neural circuits and animal behavior. Thus, from a molecular aspect, zebrafish radial glia cells are seen to be similar to mammalian astrocytes, and can therefore also be referred to as astroglia. However, a question exists as to if zebrafish astroglia cells interact functionally with neurons, in a similar way to their mammalian counterparts. Future studies of this fish will complement those on rodents and provide important information about the cellular and physiological processes underlying astroglial function that modulate neural activity and behavior in animals.

Molecular interactions of paraben family of pollutants with embryonic neuronal proteins of Danio rerio: A step ahead in computational toxicity towards adverse outcome pathway

The paraben family of endocrine disruptors exhibit persistent behaviours in aquatic matrices, having bio-accumulative effects and necessitating toxicity analysis and safe use, as well as prevention of food web penetration. In this study, the toxicity effects of 9 different parabens (Methyl, Ethyl, Propyl, Butyl, Heptyl, Isopropyl, Isobutyl, benzyl parabens and p-hydroxybenzoic acid) were studied against 17 neuronal proteins (Neurog1, Ascl1a, DLA, Syn2a, Ntn1a, Pitx2, and SoxB1, Her/Hes, Zic family) expressed during the early embryonic developmental stage of Danio rerio. The neuronal genes were selected as a biomarker to study the inhibitory effects on the cascade of genes expressed in the early developmental stage. The study uses trRossetta software to predict protein structures of neuronal genes, followed by structural refinement, energy minimisation, and active site prediction, evaluated using energy value, RC plot and ERRAT scores of PROCHECK and ERRAT programs. Compared to raw structures, highly confident predicted structures and quality scores were observed for refined protein with few exceptions. Based on the polarity and charge of the aminoacids, the probable pockets were identified using active site prediction, which were then used for molecular docking analysis. Further, the ADMET analysis, ligand likeliness and toxicological test revealed the paraben family of compounds as one of the most susceptible toxic and mutagenic compounds. The molecular docking results showed an interesting pattern of increasing binding affinity with increase in the carbon chains of paraben molecules. Benzyl Paraben showed higher binding affinities across all 17 neuronal proteins. Finally, gene co-occurrence/co-expression and protein-protein interaction studies using the STRING database depict that all proteins are functionally related and play essential roles in standard biological processes or pathways, conserved and expressed in diverse organisms. The interaction between paraben compounds and neuronal genes indicates high risks of inhibiting reactions in embryonic stages, emphasising the need for effective treatment measures and strict regulations.

The Phylotypic Brain of Vertebrates, from Neural Tube Closure to Brain Diversification

BACKGROUND

The phylotypic or intermediate stages are thought to be the most evolutionary conserved stages throughout embryonic development. The contrast with divergent early and later stages derived from the concept of the evo-devo hourglass model. Nonetheless, this developmental constraint has been studied as a whole embryo process, not at organ level. In this review, we explore brain development to assess the existence of an equivalent brain developmental hourglass. In the specific case of vertebrates, we propose to split the brain developmental stages into: (1) Early: Neurulation, when the neural tube arises after gastrulation. (2) Intermediate: Brain patterning and segmentation, when the neuromere identities are established. (3) Late: Neurogenesis and maturation, the stages when the neurons acquire their functionality. Moreover, we extend this analysis to other chordates brain development to unravel the evolutionary origin of this evo-devo constraint.

SUMMARY

Based on the existing literature, we hypothesise that a major conservation of the phylotypic brain might be due to the pleiotropy of the inductive regulatory networks, which are predominantly expressed at this stage. In turn, earlier stages such as neurulation are rather mechanical processes, whose regulatory networks seem to adapt to environment or maternal geometries. The later stages are also controlled by inductive regulatory networks, but their effector genes are mostly tissue-specific and functional, allowing diverse developmental programs to generate current brain diversity. Nonetheless, all stages of the hourglass are highly interconnected: divergent neurulation must have a vertebrate shared end product to reproduce the vertebrate phylotypic brain, and the boundaries and transcription factor code established during the highly conserved patterning will set the bauplan for the specialised and diversified adult brain.

KEY MESSAGES

The vertebrate brain is conserved at phylotypic stages, but the highly conserved mechanisms that occur during these brain mid-development stages (Inducing Regulatory Networks) are also present during other stages. Oppositely, other processes as cell interactions and functional neuronal genes are more diverse and majoritarian in early and late stages of development, respectively. These phenomena create an hourglass of transcriptomic diversity during embryonic development and evolution, with a really conserved bottleneck that set the bauplan for the adult brain around the phylotypic stage.

Angiopoietin 1 and integrin beta 1b are vital for zebrafish brain development

Introduction

Angiopoietin 1 (angpt1) is essential for angiogenesis. However, its role in neurogenesis is largely undiscovered. This study aimed to identify the role of angpt1 in brain development, the mode of action of angpt1, and its prime targets in the zebrafish brain.

Methods

We investigated the effects of embryonic brain angiogenesis and neural development using qPCR, in situ hybridization, microangiography, retrograde labeling, and immunostaining in the angpt1sa14264, itgb1bmi371, tekhu1667 mutant fish and transgenic overexpression of angpt1 in the zebrafish larval brains.

Results

We showed the co-localization of angpt1 with notch, delta, and nestin in the proliferation zone in the larval brain. Additionally, lack of angpt1 was associated with downregulation of TEK tyrosine kinase, endothelial (tek), and several neurogenic factors despite upregulation of integrin beta 1b (itgb1b), angpt2a, vascular endothelial growth factor aa (vegfaa), and glial markers. We further demonstrated that the targeted angpt1sa14264 and itgb1bmi371 mutant fish showed severely irregular cerebrovascular development, aberrant hindbrain patterning, expansion of the radial glial progenitors, downregulation of cell proliferation, deficiencies of dopaminergic, histaminergic, and GABAergic populations in the caudal hypothalamus. In contrast to angpt1sa14264 and itgb1bmi371 mutants, the tekhu1667 mutant fish regularly grew with no apparent phenotypes. Notably, the neural-specific angpt1 overexpression driven by the elavl3 (HuC) promoter significantly increased cell proliferation and neuronal progenitor cells but decreased GABAergic neurons, and this neurogenic activity was independent of its typical receptor tek.

Discussion

Our results prove that angpt1 and itgb1b, besides regulating vascular development, act as a neurogenic factor via notch and wnt signaling pathways in the neural proliferation zone in the developing brain, indicating a novel role of dual regulation of angpt1 in embryonic neurogenesis that supports the concept of angiopoietin-based therapeutics in neurological disorders.

PLASTAMINATION: Outcomes on the Central Nervous System and Reproduction

BACKGROUND

Environmental exposures to non-biodegradable and biodegradable plastics are unavoidable. Microplastics (MPs) and nanoplastics (NPs) from the manufacturing of plastics (primary sources) and the degradation of plastic waste (secondary sources) can enter the food chain directly or indirectly and, passing biological barriers, could target both the brain and the gonads. Hence, the worldwide diffusion of environmental plastic contamination (PLASTAMINATION) in daily life may represent a possible and potentially serious risk to human health.

OBJECTIVE

This review provides an overview of the effects of non-biodegradable and the more recently introduced biodegradable MPs and NPs on the brain and brain-dependent reproductive functions, summarizing the molecular mechanisms and outcomes on nervous and reproductive organs. Data from in vitro, ex vivo, non-mammalian and mammalian animal models and epidemiological studies have been reviewed and discussed.

RESULTS

MPs and NPs from non-biodegradable plastics affect organs, tissues and cells from sensitive systems such as the brain and reproductive organs. Both MPs and NPs induce oxidative stress, chronic inflammation, energy metabolism disorders, mitochondrial dysfunction and cytotoxicity, which in turn are responsible for neuroinflammation, dysregulation of synaptic functions, metabolic dysbiosis, poor gamete quality, and neuronal and reproductive toxicity. In spite of this mechanistic knowledge gained from studies of non-biodegradable plastics, relatively little is known about the adverse effects or molecular mechanisms of MPs and NPs from biodegradable plastics.

CONCLUSION

The neurological and reproductive health risks of MPs/NPs exposure warrant serious consideration, and further studies on biodegradable plastics are recommended.

Common and divergent gene regulatory networks control injury-induced and developmental neurogenesis in zebrafish retina

Following acute retinal damage, zebrafish possess the ability to regenerate all neuronal subtypes through Müller glia (MG) reprogramming and asymmetric cell division that produces a multipotent Müller glia-derived neuronal progenitor cell (MGPC). This raises three key questions. First, do MG reprogram to a developmental retinal progenitor cell (RPC) state? Second, to what extent does regeneration recapitulate retinal development? And finally, does loss of different retinal cell subtypes induce unique MG regeneration responses? We examined these questions by performing single-nuclear and single-cell RNA-Seq and ATAC-Seq in both developing and regenerating retinas. Here we show that injury induces MG to reprogram to a state similar to late-stage RPCs. However, there are major transcriptional differences between MGPCs and RPCs, as well as major transcriptional differences between activated MG and MGPCs when different retinal cell subtypes are damaged. Validation of candidate genes confirmed that loss of different subtypes induces differences in transcription factor gene expression and regeneration outcomes.

Homemade: building the structure of the neurogenic niche

Neural stem/progenitor cells live in an intricate cellular environment, the neurogenic niche, which supports their function and enables neurogenesis. The niche is made of a diversity of cell types, including neurons, glia and the vasculature, which are able to signal to and are structurally organised around neural stem/progenitor cells. While the focus has been on how individual cell types signal to and influence the behaviour of neural stem/progenitor cells, very little is actually known on how the niche is assembled during development from multiple cellular origins, and on the role of the resulting topology on these cells. This review proposes to draw a state-of-the art picture of this emerging field of research, with the aim to expose our knowledge on niche architecture and formation from different animal models (mouse, zebrafish and fruit fly). We will span its multiple aspects, from the existence and importance of local, adhesive interactions to the potential emergence of larger-scale topological properties through the careful assembly of diverse cellular and acellular components.

Embryonic exposure to decitabine induces multiple neural tube defects in developing zebrafish

Neural tube defects are severe congenital disorders of the central nervous system that originate during embryonic development when the neural tube fails to close completely. It affects one to two infants per 1000 births. The aetiology is multifactorial with contributions from both genetic and environmental factors. Dysregulated epigenetic mechanisms, in particular the abnormal genome-wide methylation during embryogenesis, have been linked to developmental abnormalities including neural tube defects. The current study investigated the influence of decitabine (DCT), a DNA methylation inhibitor, on embryonic development in zebrafish, with a focus on neural tube formation. The developing zebrafish embryos were exposed to graded concentrations of decitabine (from 13.69 μM to 1 mM) before the onset of neurulation. The developmental process was monitored at regular time intervals post fertilization. At 120 h post fertilization, the developing embryos were inspected individually to determine the incidence and severity of neural tube defects. Using alizarin red staining, the cranial and caudal neural tube morphology was examined in formaldehyde fixed larvae. Anomalies in neural tube and somite development, as well as a delay in hatching, were discovered at an early stage of development. As development continued, neural tube defects became increasingly evident, and there was a concentration-dependent rise in the prevalence and severity of various neural tube defects. 90% of growing embryos in the group exposed to decitabine 1 mM had multiple neural tube malformations, and 10% had isolated neural tube defects. With several abnormalities, the caudal region of the neural tube was seriously compromised. The histopathological studies supported the malformations in neural tube. Our study revealed the harmful impact of decitabine on the development of the neural tube in growing zebrafish. Moreover, these findings support the hypothesis that the hypomethylation during embryonic development causes neural tube defects.

Imaging the radioprotective effect of amifostine in the developing brain using an apoptosis-reporting transgenic zebrafish

PURPOSE

Normal tissue radioprotectants alleviate radiation-induced damages and preserve critical organ functions. Investigating their efficacy in vivo remains challenging, especially in enclosed organs like the brain. An animal model that enables direct visualization of radiation-induced apoptosis while possessing the structural complexity of a vertebrate brain facilitates these studies in a precise and effective manner.

MATERIALS AND METHODS

We employed a secA5 transgenic zebrafish expressing secreted Annexin V fused with a yellow fluorescent protein to visualize radiation-induced apoptosis in vivo. We developed a semi-automated imaging method for standardized acquisition of apoptosis signals in batches of zebrafish larvae. Using these approaches, we studied the protective effect of amifostine (WR-2721) in the irradiated zebrafish larval brain.

RESULTS

Upon 2 Gy total-body 137Cs irradiation, increased apoptosis could be visualized at high resolution in the secA5 brain at 2, 24, and 48 hour post irradiation (hpi). Amifostine treatment (4 mM) during irradiation reduced apoptosis significantly at 24 hpi and preserved Wnt active cells in the larval brain. When the 2 Gy irradiation was delivered in combination with cisplatin treatment (0.1 mM), the radioprotective effect of amifostine was also observed.

CONCLUSIONS

Our study reveals the radioprotective effect of amifostine in the developing zebrafish larval brain, and highlights the utility of secA5 transgenic zebrafish as a novel system for investigating normal tissue radioprotectants in vivo.

Toxic effects of benfluralin on zebrafish embryogenesis via the accumulation of reactive oxygen species and apoptosis

The dinitroaniline herbicide benfluralin is used weed control in conventional systems and poses a high risk of accumulation in aquatic systems. Previous studies have shown the toxic effects of benfluralin on non-target organisms; however, its developmental toxicity in vertebrates has not yet been reported. This study demonstrated the developmental toxicity of benfluralin and its mechanism of action, using zebrafish as an aquatic vertebrate model. Benfluralin induces morphological and physiological alterations in body length, yolk sac, and heart edema. We also demonstrated a reactive oxygen species (ROS) increase of approximately 325.53 % compared with the control group after 20 μM benfluralin-treatment. In addition, the malformation of the heart and vascular structures was identified using transgenic flk1:eGFP zebrafish models at 20 μM concentration benfluralin exposure. Moreover, benfluralin induced small livers, approximately 59.81 % of normal liver size, via abnormal development of the liver as observed in the transgenic L-fabp:dsRed zebrafish. Benfluralin also inhibits normal growth via abnormal expression of cell cycle regulatory genes and increases oxidative stress, inflammation, and apoptosis. Collectively, we elucidated the mechanisms associated with benfluralin toxicity, which lead to various abnormalities and developmental toxicities in zebrafish. Therefore, this study provides information on the parameters used to assess developmental toxicity in other aquatic organisms, such as herbicides, pesticides, and environmental contaminants.

Assessing Drug Administration Techniques in Zebrafish Models of Neurological Disease

Neurological diseases, including neurodegenerative and neurodevelopmental disorders, affect nearly one in six of the world's population. The burden of the resulting deaths and disability is set to rise during the next few decades as a consequence of an aging population. To address this, zebrafish have become increasingly prominent as a model for studying human neurological diseases and exploring potential therapies. Zebrafish offer numerous benefits, such as genetic homology and brain similarities, complementing traditional mammalian models and serving as a valuable tool for genetic screening and drug discovery. In this comprehensive review, we highlight various drug delivery techniques and systems employed for therapeutic interventions of neurological diseases in zebrafish, and evaluate their suitability. We also discuss the challenges encountered during this process and present potential advancements in innovative techniques.

Developmental Exposure to Kynurenine Affects Zebrafish and Rat Behavior

Proper nutrition and supplementation during pregnancy and breastfeeding are crucial for the development of offspring. Kynurenine (KYN) is the central metabolite of the kynurenine pathway and a direct precursor of other metabolites that possess immunoprotective or neuroactive properties, with the ultimate effect on fetal neurodevelopment. To date, no studies have evaluated the effects of KYN on early embryonic development. Thus, the aim of our study was to determine the effect of incubation of larvae with KYN in different developmental periods on the behavior of 5-day-old zebrafish. Additionally, the effects exerted by KYN administered on embryonic days 1-7 (ED 1-7) on the behavior of adult offspring of rats were elucidated. Our study revealed that the incubation with KYN induced changes in zebrafish behavior, especially when zebrafish embryos or larvae were incubated with KYN from 1 to 72 h post-fertilization (hpf) and from 49 to 72 hpf. KYN administered early during pregnancy induced subtle differences in the neurobehavioral development of adult offspring. Further research is required to understand the mechanism of these changes. The larval zebrafish model can be useful for studying disturbances in early brain development processes and their late behavioral consequences. The zebrafish-medium system may be applicable in monitoring drug metabolism in zebrafish.

Directed Neural Stem Cells Differentiation via Signal Communication with Ni-Zn Micromotors

Neural stem cells (NSCs), with the capability of self-renewal, differentiation, and environment modulation, are considered promising for stroke, brain injury therapy, and neuron regeneration. Activation of endogenous NSCs, is attracting increasing research enthusiasm, which avoids immune rejection and ethical issues of exogenous cell transplantation. Yet, how to induce directed growth and differentiation in situ remain a major challenge. In this study, a pure water-driven Ni-Zn micromotor via a self-established electric-chemical field is proposed. The micromotors can be magnetically guided and precisely approach target NSCs. Through the electric-chemical field, bioelectrical signal exchange and communication with endogenous NSCs are allowed, thus allowing for regulated proliferation and directed neuron differentiation in vivo. Therefore, the Ni-Zn micromotor provides a platform for controlling cell fate via a self-established electrochemical field and targeted activation of endogenous NSCs.

Zebrafish as an emerging model to study estrogen receptors in neural development

Estrogens induce several regulatory signals in the nervous system that are mainly mediated through estrogen receptors (ERs). ERs are largely expressed in the nervous system, yet the importance of ERs to neural development has only been elucidated over the last decades. Accumulating evidence shows a fundamental role for estrogens in the development of the central and peripheral nervous systems, hence, the contribution of ERs to neural function is now a growing area of research. The conservation of the structure of the ERs and their response to estrogens make the zebrafish an interesting model to dissect the role of estrogens in the nervous system. In this review, we highlight major findings of ER signaling in embryonic zebrafish neural development and compare the similarities and differences to research in rodents. We also discuss how the recent generation of zebrafish ER mutants, coupled with the availability of several transgenic reporter lines, its amenability to pharmacological studies and in vivo live imaging, could help us explore ER function in embryonic neural development.

A CRISPR-Cas9 mutation in sox9b long intergenic noncoding RNA (slincR) affects zebrafish development, behavior, and regeneration

The role of long noncoding RNAs (lncRNAs) regulators of toxicological responses to environmental chemicals is gaining prominence. Previously, our laboratory discovered an lncRNA, sox9b long intergenic noncoding RNA (slincR), that is activated by multiple ligands of aryl hydrocarbon receptor (AHR). Within this study, we designed a CRISPR-Cas9-mediated slincR zebrafish mutant line to better understand its biological function in presence or absence of a model AHR ligand, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The slincRosu3 line contains an 18 bp insertion within the slincR sequence that changes its predicted mRNA secondary structure. Toxicological profiling showed that slincRosu3 is equally or more sensitive to TCDD for morphological and behavioral phenotypes. Embryonic mRNA-sequencing showed differential responses of 499 or 908 genes in slincRosu3 in absence or presence of TCDD Specifically, unexposed slincRosu3 embryos showed disruptions in metabolic pathways, suggesting an endogenous role for slincR. slincRosu3 embryos also had repressed mRNA levels of sox9b-a transcription factor that slincR is known to negatively regulate. Hence, we studied cartilage development and regenerative capacity-both processes partially regulated by sox9b. Cartilage development was disrupted in slincRosu3 embryos both in presence and absence of TCDD. slincRosu3 embryos also displayed a lack of regenerative capacity of amputated tail fins, accompanied by a lack of cell proliferation. In summary, using a novel slincR mutant line, we show that a mutation in slincR can have widespread impacts on gene expression and structural development endogenously and limited, but significant impacts in presence of AHR induction that further highlights its importance in the developmental process.

Longitudinal effects of ketamine on cell proliferation and death in the CNS of zebrafish

Zebrafish is known for its widespread neurogenesis and regenerative capacity, as well as several biological advantages, which turned it into a relevant animal model in several areas of research, namely in toxicological studies. Ketamine is a well-known anesthetic used both in human as well as veterinary medicine, due to its safety, short duration and unique mode of action. However, ketamine administration is associated with neurotoxic effects and neuronal death, which renders its use on pediatric medicine problematic. Thus, the evaluation of ketamine effects administration at early stages of neurogenesis is of pivotal importance. The 1-4 somites stage of zebrafish embryo development corresponds to the beginning of segmentation and formation of neural tube. In this species, as well as in other vertebrates, longitudinal studies are scarce, and the evaluation of ketamine long-term effects in adults is poorly understood. This study aimed to assess the effects of ketamine administration at the 1-4 somites stage, both in subanesthetic and anesthetic concentrations, in brain cellular proliferation, pluripotency and death mechanisms in place during early and adult neurogenesis. For that purpose, embryos at the 1-4 somites stage (10,5hours post fertilization - hpf) were distributed into study groups and exposed for 20minutes to ketamine concentrations at 0.2/0.8mg/mL. Animals were grown until defined check points, namely 50 hpf, 144 hpf and 7 months adults. The assessment of the expression and distribution patterns of proliferating cell nuclear antigen (PCNA), of sex-determining region Y-box 2 (Sox 2), apoptosis-inducing factor (AIF) and microtubule-associated protein 1 light chain 3 (LC3) was performed by Western-blot and immunohistochemistry. The results evidenced the main alterations in 144 hpf larvae, namely in autophagy and in cellular proliferation at the highest concentration of ketamine (0.8mg/mL). Nonetheless, in adults no significant alterations were seen, pointing to a return to a homeostatic stage. This study allowed clarifying some of the aspects pertaining the longitudinal effects of ketamine administration regarding the CNS capacity to proliferate and activate the appropriate cell death and repair mechanisms leading to homeostasis in zebrafish. Moreover, the results indicate that ketamine administration at 1-4 somites stage in the subanesthetic and anesthetic concentrations despite some transitory detrimental effects at 144 hpf, is long-term safe for CNS, which are newly and promising results in this research field.

In a zebrafish biomedical model of human Allan-Herndon-Dudley syndrome impaired MTH signaling leads to decreased neural cell diversity

Background

Maternally derived thyroid hormone (T3) is a fundamental factor for vertebrate neurodevelopment. In humans, mutations on the thyroid hormones (TH) exclusive transporter monocarboxylic acid transporter 8 (MCT8) lead to the Allan-Herndon-Dudley syndrome (AHDS). Patients with AHDS present severe underdevelopment of the central nervous system, with profound cognitive and locomotor consequences. Functional impairment of zebrafish T3 exclusive membrane transporter Mct8 phenocopies many symptoms observed in patients with AHDS, thus providing an outstanding animal model to study this human condition. In addition, it was previously shown in the zebrafish mct8 KD model that maternal T3 (MTH) acts as an integrator of different key developmental pathways during zebrafish development.

Methods

Using a zebrafish Mct8 knockdown model, with consequent inhibition of maternal thyroid hormones (MTH) uptake to the target cells, we analyzed genes modulated by MTH by qPCR in a temporal series from the start of segmentation through hatching. Survival (TUNEL) and proliferation (PH3) of neural progenitor cells (dla, her2) were determined, and the cellular distribution of neural MTH-target genes in the spinal cord during development was characterized. In addition, in-vivo live imaging was performed to access NOTCH overexpression action on cell division in this AHDS model. We determined the developmental time window when MTH is required for appropriate CNS development in the zebrafish; MTH is not involved in neuroectoderm specification but is fundamental in the early stages of neurogenesis by promoting the maintenance of specific neural progenitor populations. MTH signaling is required for developing different neural cell types and maintaining spinal cord cytoarchitecture, and modulation of NOTCH signaling in a non-autonomous cell manner is involved in this process.

Discussion

The findings show that MTH allows the enrichment of neural progenitor pools, regulating the cell diversity output observed by the end of embryogenesis and that Mct8 impairment restricts CNS development. This work contributes to the understanding of the cellular mechanisms underlying human AHDS.

Exposure to Tetrabutylammonium Bromide Impairs Cranial Neural Crest Specification, Neurogenic Program, and Brain Morphogenesis

Tetrabutylammonium bromide (TBAB) is a widely used industrial reagent and is commonly found in our aquatic ecosystem as an industrial byproduct. In humans, the ingestion of TBAB causes severe neurological impairments and disorders such as vertigo, hallucinations, and delirium. Yet, the extent of environmental risk and TBAB toxicity to human health is poorly understood. In this study, we aim to determine the developmental toxicity of TBAB using zebrafish embryos as a model and provide novel insights into the mechanism of action of such chemicals on neurodevelopment and the overall embryonic program. Our results show that exposure to TBAB results in impaired development of the brain, inner ear, and pharyngeal skeletal elements in the zebrafish embryo. TBAB treatment resulted in aberrations in the specification of the neural crest precursors, hindbrain segmentation, and otic neurogenesis. TBAB treatment also induced a surge in apoptosis in the head, tail, and trunk regions of the developing embryo. Long-term TBAB exposure resulted in cardiac edema and craniofacial defects. Further, in silico molecular docking analysis indicated that TBAB binds to AMPA receptors and modulates neural developmental genes such as olfactomedin and acetylcholinesterase in the embryonic brain. To summarize, our study highlights the novel effects of TBAB on embryonic brain formation and segmentation, ear morphogenesis, and craniofacial skeletal development.

Smuggling on the Nanoscale-Fusogenic Liposomes Enable Efficient RNA-Transfer with Negligible Immune Response In Vitro and In Vivo

The efficient and biocompatible transfer of nucleic acids into mammalian cells for research applications or medical purposes is a long-standing, challenging task. Viral transduction is the most efficient transfer system, but often entails high safety levels for research and potential health impairments for patients in medical applications. Lipo- or polyplexes are commonly used transfer systems but result in comparably low transfer efficiencies. Moreover, inflammatory responses caused by cytotoxic side effects were reported for these transfer methods. Often accountable for these effects are various recognition mechanisms for transferred nucleic acids. Using commercially available fusogenic liposomes (Fuse-It-mRNA), we established highly efficient and fully biocompatible transfer of RNA molecules for in vitro as well as in vivo applications. We demonstrated bypassing of endosomal uptake routes and, therefore, of pattern recognition receptors that recognize nucleic acids with high efficiency. This may underlie the observed almost complete abolishment of inflammatory cytokine responses. RNA transfer experiments into zebrafish embryos and adult animals fully confirmed the functional mechanism and the wide range of applications from single cells to organisms.

The importance of thyroid hormone signaling during early development: Lessons from the zebrafish model

The zebrafish is an optimal experimental model to study thyroid hormone (TH) involvement in vertebrate development. The use of state-of-the-art zebrafish genetic tools available for the study of the effect of gene silencing, cell fate decisions and cell lineage differentiation have contributed to a more insightful comprehension of molecular, cellular, and tissue-specific TH actions. In contrast to intrauterine development, extrauterine embryogenesis observed in zebrafish has facilitated a more detailed study of the development of the hypothalamic-pituitary-thyroid axis. This model has also enabled a more insightful analysis of TH molecular actions upon the organization and function of the brain, the retina, the heart, and the immune system. Consequently, zebrafish has become a trendy model to address paradigms of TH-related functional and biomedical importance. We here compilate the available knowledge regarding zebrafish developmental events for which specific components of TH signaling are essential.

Olfactory detection of viruses shapes brain immunity and behavior in zebrafish

Olfactory sensory neurons (OSNs) are constantly exposed to pathogens, including viruses. However, serious brain infection via the olfactory route rarely occurs. When OSNs detect a virus, they coordinate local antiviral immune responses to stop virus progression to the brain. Despite effective immune control in the olfactory periphery, pathogen-triggered neuronal signals reach the CNS via the olfactory bulb (OB). We hypothesized that neuronal detection of a virus by OSNs initiates neuroimmune responses in the OB that prevent pathogen invasion. Using zebrafish ( Danio rerio ) as a model, we demonstrate viral-specific neuronal activation of OSNs projecting into the OB, indicating that OSNs are electrically activated by viruses. Further, behavioral changes are seen in both adult and larval zebrafish after viral exposure. By profiling the transcription of single cells in the OB after OSNs are exposed to virus, we found that both microglia and neurons enter a protective state. Microglia and macrophage populations in the OB respond within minutes of nasal viral delivery followed decreased expression of neuronal differentiation factors and enrichment of genes in the neuropeptide signaling pathway in neuronal clusters. Pituitary adenylate-cyclase-activating polypeptide ( pacap ), a known antimicrobial, was especially enriched in a neuronal cluster. We confirm that PACAP is antiviral in vitro and that PACAP expression increases in the OB 1 day post-viral treatment. Our work reveals how encounters with viruses in the olfactory periphery shape the vertebrate brain by inducing antimicrobial programs in neurons and by altering host behavior.

High-throughput functional analysis of autism genes in zebrafish identifies convergence in dopaminergic and neuroimmune pathways

Advancing from gene discovery in autism spectrum disorders (ASDs) to the identification of biologically relevant mechanisms remains a central challenge. Here, we perform parallel in vivo functional analysis of 10 ASD genes at the behavioral, structural, and circuit levels in zebrafish mutants, revealing both unique and overlapping effects of gene loss of function. Whole-brain mapping identifies the forebrain and cerebellum as the most significant contributors to brain size differences, while regions involved in sensory-motor control, particularly dopaminergic regions, are associated with altered baseline brain activity. Finally, we show a global increase in microglia resulting from ASD gene loss of function in select mutants, implicating neuroimmune dysfunction as a key pathway relevant to ASD biology.

Different developmental insecticide exposure windows trigger distinct locomotor phenotypes in the early life stages of zebrafish

Due to their extensive use and high biological activity, insecticides largely contribute to loss of biodiversity and environmental pollution. The regulation of insecticides by authorities is mainly focused on lethal concentrations. However, sub-lethal effects such as alterations in behavior and neurodevelopment can significantly affect the fitness of individual fish and their population dynamics and therefore deserve consideration. Moreover, it is important to understand the impact of exposure timing during development, about which there is currently a lack of relevant knowledge. Here, we investigated whether there are periods during neurodevelopment of fish, which are particularly vulnerable to insecticide exposure. Therefore, we exposed zebrafish embryos to six different insecticides with cholinergic mode of action for 24 h during different periods of neurodevelopment and measured locomotor output using an age-matched behavior assay. We used the organophosphates diazinon and dimethoate, the carbamates pirimicarb and methomyl as well as the neonicotinoids thiacloprid and imidacloprid because they are abundant in the environment and cholinergic signaling plays a major role during key processes of neurodevelopment. We found that early embryonic motor behaviors, as measured by spontaneous tail coiling, increased upon exposure to most insecticides, while later movements, measured through touch-evoked response and a light-dark transition assay, rather decreased for the same insecticides and exposure duration. Moreover, the observed effects were more pronounced when exposure windows were temporally closer to the performing of the respective behavioral assay. However, the measured behavioral effects recovered after a short period, indicating that none of the exposure windows chosen here are particularly critical, but rather that insecticides acutely interfere with neuronal function at all stages as long as they are present. Overall, our results contribute to a better understanding of risks posed by cholinergic insecticides to fish and provide an important basis for the development of safe regulations to improve environmental health.