Zebrafish lacking Alzheimer presenilin enhancer 2 (Pen-2) demonstrate excessive p53-dependent apoptosis and neuronal loss

Zebrafish models for studying cognitive enhancers

Cognitive decline is commonly seen both in normal aging and in neurodegenerative and neuropsychiatric diseases. Various experimental animal models represent a valuable tool to study brain cognitive processes and their deficits. Equally important is the search for novel drugs to treat cognitive deficits and improve cognitions. Complementing rodent and clinical findings, studies utilizing zebrafish (Danio rerio) are rapidly gaining popularity in translational cognitive research and neuroactive drug screening. Here, we discuss the value of zebrafish models and assays for screening nootropic (cognitive enhancer) drugs and the discovery of novel nootropics. We also discuss the existing challenges, and outline future directions of research in this field.

Alzheimer's Disease: Models and Molecular Mechanisms Informing Disease and Treatments

Alzheimer's Disease (AD) is a complex neurodegenerative disease resulting in progressive loss of memory, language and motor abilities caused by cortical and hippocampal degeneration. This review captures the landscape of understanding of AD pathology, diagnostics, and current therapies. Two major mechanisms direct AD pathology: (1) accumulation of amyloid β (Aβ) plaque and (2) tau-derived neurofibrillary tangles (NFT). The most common variants in the Aβ pathway in APP, PSEN1, and PSEN2 are largely responsible for early-onset AD (EOAD), while MAPT, APOE, TREM2 and ABCA7 have a modifying effect on late-onset AD (LOAD). More recent studies implicate chaperone proteins and Aβ degrading proteins in AD. Several tests, such as cognitive function, brain imaging, and cerebral spinal fluid (CSF) and blood tests, are used for AD diagnosis. Additionally, several biomarkers seem to have a unique AD specific combination of expression and could potentially be used in improved, less invasive diagnostics. In addition to genetic perturbations, environmental influences, such as altered gut microbiome signatures, affect AD. Effective AD treatments have been challenging to develop. Currently, there are several FDA approved drugs (cholinesterase inhibitors, Aß-targeting antibodies and an NMDA antagonist) that could mitigate AD rate of decline and symptoms of distress.

Zebrafish Experimental Animal Models for AD: A Comprehensive Review

AD disease (AD) is a multifaceted and intricate neurodegenerative disorder characterized by intracellular neurofibrillary tangle (NFT) formation and the excessive production and deposition of Aβ senile plaques. While transgenic AD models have been found instrumental in unravelling AD pathogenesis, they involve cost and time constraints during the preclinical phase. Zebrafish, owing to their simplicity, well-defined behavioural patterns, and relevance to neurodegenerative research, have emerged as a promising complementary model. Zebrafish possess glutaminergic and cholinergic pathways implicated in learning and memory, actively contributing to our understanding of neural transmission processes. This review sheds light on the molecular mechanisms by which various neurotoxic agents, including okadaic acid (OKA), cigarette smoke extract, metals, and transgenic zebrafish models with genetic similarities to AD patients, induce cognitive impairments and neuronal degeneration in mammalian systems. These insights may facilitate the identification of effective neurotoxic agents for replicating AD pathogenesis in the zebrafish brain. In this comprehensive review, the pivotal role of zebrafish models in advancing our comprehension of AD is emphasized. These models hold immense potential for shaping future research directions and clinical interventions, ultimately contributing to the development of novel AD therapies.

SAMPL is a high-throughput solution to study unconstrained vertical behavior in small animals

Balance and movement are impaired in many neurological disorders. Recent advances in behavioral monitoring provide unprecedented access to posture and locomotor kinematics but without the throughput and scalability necessary to screen candidate genes/potential therapeutics. Here, we present a scalable apparatus to measure posture and locomotion (SAMPL). SAMPL includes extensible hardware and open-source software with real-time processing and can acquire data from D. melanogaster, C. elegans, and D. rerio as they move vertically. Using SAMPL, we define how zebrafish balance as they navigate vertically and discover small but systematic variations among kinematic parameters between genetic backgrounds. We demonstrate SAMPL's ability to resolve differences in posture and navigation as a function of effect size and data gathered, providing key data for screens. SAMPL is therefore both a tool to model balance and locomotor disorders and an exemplar of how to scale apparatus to support screens.

Notch pathway is required for protection against heat stress in spermatogonial stem cells in medaka

Gamete production is a fundamental process for reproduction; however, exposure to stress, such as increased environmental temperature, can decrease or even interrupt this process, affecting fertility. Thus, the survival of spermatogonial stem cells (SSCs) is crucial for the recovery of spermatogenesis upon stressful situations. Here, we show that the Notch pathway is implicated in such survival, by protecting the SSCs against thermal stress. First, we corroborated the impairment of spermatogenesis under heat stress in medaka, observing an arrest in metaphase I at 10 days of heat treatment, an increase in the number of spermatocytes, and downregulation of ndrg1b and sycp3. In addition, at 30 days of treatment, an interruption of spermatogenesis was observed with a strong loss of spermatocytes and spermatids. Then, the exposure of adult males to thermal stress condition induced apoptosis mainly in spermatogenic and supporting somatic cells, with the exception of the germinal region, where SSCs are located. Concomitantly, the Notch pathway-related genes were upregulated, including the ligands (dll4, jag1-2) and receptors (notch1a-3). Moreover, during thermal stress presenilin enhancer-2 (pen-2), the catalytic subunit of γ-secretase complex of the Notch pathway was restricted to the germinal region of the medaka testis, observed in somatic cells surrounding type A spermatogonia (SGa). The importance of Notch pathway was further supported by an ex vivo approach, in which the inhibition of this pathway activity induced a loss of SSCs. Overall, this study supports the importance of Notch pathways for the protection of SSCs under chronic thermal stress.

Zebrafish as a Model Organism for Studying Pathologic Mechanisms of Neurodegenerative Diseases and other Neural Disorders

Zebrafish are widely considered an excellent vertebrate model for studying the pathogenesis of human diseases because of their transparency of embryonic development, easy breeding, high similarity with human genes, and easy gene manipulation. Previous studies have shown that zebrafish as a model organism provides an ideal operating platform for clarifying the pathological and molecular mechanisms of neurodegenerative diseases and related human diseases. This review mainly summarizes the achievements and prospects of zebrafish used as model organisms in the research of neurodegenerative diseases and other human diseases related to the nervous system in recent years. In the future study of human disease mechanisms, the application of the zebrafish model will continue to provide a valuable operating platform and technical support for investigating and finding better prevention and treatment of these diseases, which has broad application prospects and practical significance. Zebrafish models used in neurodegenerative diseases and other diseases related to the nervous system.

Scalable Apparatus to Measure Posture and Locomotion (SAMPL): a high-throughput solution to study unconstrained vertical behavior in small animals

Balance and movement are impaired in a wide variety of neurological disorders. Recent advances in behavioral monitoring provide unprecedented access to posture and locomotor kinematics, but without the throughput and scalability necessary to screen candidate genes / potential therapeutics. We present a powerful solution: a Scalable Apparatus to Measure Posture and Locomotion (SAMPL). SAMPL includes extensible imaging hardware and low-cost open-source acquisition software with real-time processing. We first demonstrate that SAMPL's hardware and acquisition software can acquire data from from D. melanogaster, C. elegans, and D. rerio as they move vertically. Next, we leverage SAMPL's throughput to rapidly (two weeks) gather a new zebrafish dataset. We use SAMPL's analysis and visualization tools to replicate and extend our current understanding of how zebrafish balance as they navigate through a vertical environment. Next, we discover (1) that key kinematic parameters vary systematically with genetic background, and (2) that such background variation is small relative to the changes that accompany early development. Finally, we simulate SAMPL's ability to resolve differences in posture or vertical navigation as a function of affect size and data gathered -- key data for screens. Taken together, our apparatus, data, and analysis provide a powerful solution for labs using small animals to investigate balance and locomotor disorders at scale. More broadly, SAMPL is both an adaptable resource for labs looking process videographic measures of behavior in real-time, and an exemplar of how to scale hardware to enable the throughput necessary for screening.

Unraveling Presenilin 2 Functions in a Knockout Zebrafish Line to Shed Light into Alzheimer's Disease Pathogenesis

Mutations in presenilin 2 (PS2) have been causally linked to the development of inherited Alzheimer's disease (AD). Besides its role as part of the γ-secretase complex, mammalian PS2 is also involved, as an individual protein, in a growing number of cell processes, which result altered in AD. To gain more insight into PS2 (dys)functions, we have generated a presenilin2 (psen2) knockout zebrafish line. We found that the absence of the protein does not markedly influence Notch signaling at early developmental stages, suggesting a Psen2 dispensable role in the γ-secretase-mediated Notch processing. Instead, loss of Psen2 induces an exaggerated locomotor response to stimulation in fish larvae, a reduced number of ER-mitochondria contacts in zebrafish neurons, and an increased basal autophagy. Moreover, the protein is involved in mitochondrial axonal transport, since its acute downregulation reduces in vivo organelle flux in zebrafish sensory neurons. Importantly, the expression of a human AD-linked mutant of the protein increases this vital process. Overall, our results confirm zebrafish as a good model organism for investigating PS2 functions in vivo, representing an alternative tool for the characterization of new AD-linked defective cell pathways and the testing of possible correcting drugs.

Zebrafish: A Model Deciphering the Impact of Flavonoids on Neurodegenerative Disorders

Over the past century, advances in biotechnology, biochemistry, and pharmacognosy have spotlighted flavonoids, polyphenolic secondary metabolites that have the ability to modulate many pathways involved in various biological mechanisms, including those involved in neuronal plasticity, learning, and memory. Moreover, flavonoids are known to impact the biological processes involved in developing neurodegenerative diseases, namely oxidative stress, neuroinflammation, and mitochondrial dysfunction. Thus, several flavonoids could be used as adjuvants to prevent and counteract neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Zebrafish is an interesting model organism that can offer new opportunities to study the beneficial effects of flavonoids on neurodegenerative diseases. Indeed, the high genome homology of 70% to humans, the brain organization largely similar to the human brain as well as the similar neuroanatomical and neurochemical processes, and the high neurogenic activity maintained in the adult brain makes zebrafish a valuable model for the study of human neurodegenerative diseases and deciphering the impact of flavonoids on those disorders.

Methylation differences in Alzheimer's disease neuropathologic change in the aged human brain

Alzheimer's disease (AD) is the most common cause of dementia with advancing age as its strongest risk factor. AD neuropathologic change (ADNC) is known to be associated with numerous DNA methylation changes in the human brain, but the oldest old (> 90 years) have so far been underrepresented in epigenetic studies of ADNC. Our study participants were individuals aged over 90 years (n = 47) from The 90+ Study. We analyzed DNA methylation from bulk samples in eight precisely dissected regions of the human brain: middle frontal gyrus, cingulate gyrus, entorhinal cortex, dentate gyrus, CA1, substantia nigra, locus coeruleus and cerebellar cortex. We deconvolved our bulk data into cell-type-specific (CTS) signals using computational methods. CTS methylation differences were analyzed across different levels of ADNC. The highest amount of ADNC related methylation differences was found in the dentate gyrus, a region that has so far been underrepresented in large scale multi-omic studies. In neurons of the dentate gyrus, DNA methylation significantly differed with increased burden of amyloid beta (Aβ) plaques at 5897 promoter regions of protein-coding genes. Amongst these, higher Aβ plaque burden was associated with promoter hypomethylation of the Presenilin enhancer 2 (PEN-2) gene, one of the rate limiting genes in the formation of gamma-secretase, a multicomponent complex that is responsible in part for the endoproteolytic cleavage of amyloid precursor protein into Aβ peptides. In addition to novel ADNC related DNA methylation changes, we present the most detailed array-based methylation survey of the old aged human brain to date. Our open-sourced dataset can serve as a brain region reference panel for future studies and help advance research in aging and neurodegenerative diseases.

Loxhd1b inhibits the hair cell development in zebrafish: Possible relation to the BDNF/TrkB/ERK pathway

Background

Mutations in lipoxygenase homology domain 1 (LOXHD1) cause autosomal recessive inheritance, leading to high-frequency and intermediate-frequency hearing losses in patients. To date, studies on the localization of LOXHD1 gene expression are limited. In this study, we aimed to observe the expressions of Loxhd1b in zebrafish, C57BL/6 murine cochlea, and HEI-OC1 cells.

Methods

The expression of Loxhd1b in the auditory system of zebrafish was explored by in situ hybridization experiments of zebrafish embryos. The expression of Loxhd1b in cochlear and HEI-OC1 cells of C57BL/6 mice was analyzed by immunofluorescence staining. Confocal microscopic in vivo imaging was used to detect the number and morphological characteristics of lateral line neuromasts and inner ear hair cells in zebrafish that knocked down Loxhd1b gene. The effect of knockdown Loxhd1b gene on the development of zebrafish otolith and semicircular canal was observed using microscopic. Transcriptome sequencing was used to identify downstream molecules and associated signaling pathways and validated by western blotting, immunostaining, and rescue experiments.

Results

Results of the in situ hybridization with zebrafish embryos at different time points showed that Loxhd1b was expressed in zebrafish at the inner ear and olfactory pores, while the immunostaining showed that Loxhd1 was expressed in both C57BL/6 mouse cochlea and HEI-OC1 cells. Loxhd1b knockdown causes a decrease in the number of spinal and lateral line neuromasts in the inner ear of zebrafish, accompanied by weakened hearing function, and also leads to developmental defects of otoliths and ear follicles. The results of transcriptomics analysis revealed the downstream molecule brain-derived neurotrophic factor (BDNF) and verified that Loxhd1b and BDNF regulate the formation of zebrafish hair cells by synergistic regulation of BDNF/TrkB/ERK pathway based on western blotting, immunostaining, and rescue experiments.

Conclusion

This was the first time that the BDNF/TrkB/ERK pathway was identified to play a critical role in the molecular regulation of the development of zebrafish hair cells and the auditory development by Loxhd1b.

Zebrafish as a model organism for neurodegenerative disease

The zebrafish is increasingly recognized as a model organism for translational research into human neuropathology. The zebrafish brain exhibits fundamental resemblance with human neuroanatomical and neurochemical pathways, and hallmarks of human brain pathology such as protein aggregation, neuronal degeneration and activation of glial cells, for example, can be modeled and recapitulated in the fish central nervous system. Genetic manipulation, imaging, and drug screening are areas where zebrafish excel with the ease of introducing mutations and transgenes, the expression of fluorescent markers that can be detected in vivo in the transparent larval stages overtime, and simple treatment of large numbers of fish larvae at once followed by automated screening and imaging. In this review, we summarize how zebrafish have successfully been employed to model human neurodegenerative diseases such as Parkinson’s disease, Alzheimer’s disease, amyotrophic lateral sclerosis, and Huntington’s disease. We discuss advantages and disadvantages of choosing zebrafish as a model for these neurodegenerative conditions.

Modeling neurodegenerative disorders in zebrafish

Neurodegeneration is a major cause of Alzheimer's, Parkinson's, Huntington's, multiple and amyotrophic lateral sclerosis, pontocerebellar hypoplasia, dementia and other related brain disorders. Their complex pathogenesis commonly includes genetic and neurochemical deficits, misfolded protein toxicity, demyelination, apoptosis and mitochondrial dysfunctions. Albeit differing in specific underlying mechanisms, neurodegenerative disorders typically display evolutionarily conserved mechanisms across taxa. Here, we review the role of zebrafish models in recapitulating major human and rodent neurodegenerative conditions, demonstrating this species as a highly relevant experimental model for research on neurodegenerative diseases, and discussing how these fish models can further clarify the underlying genetic, neurochemical, neuroanatomical and behavioral pathogenic mechanisms.

Physiology and pharmacology of amyloid precursor protein

Amyloid precursor protein (APP) is an evolutionarily conserved transmembrane protein and a well-characterized precursor protein of amyloid-beta (Aβ) peptides, which accumulate in the brains of individuals with Alzheimer's disease (AD)-related pathologies. Aβ has been extensively investigated since the amyloid hypothesis in AD was proposed. Besides Aβ, previous studies on APP and its proteolytic cleavage products have suggested their diverse pathological and physiological functions. However, their roles still have not been thoroughly understood. In this review, we extensively discuss the evolutionarily-conserved biology of APP, including its structure and processing pathway, as well as recent findings on the physiological roles of APP and its fragments in the central nervous system and peripheral nervous system. We have also elaborated upon the current status of APP-targeted therapeutic approaches for AD treatment by discussing inhibitors of several proteases participating in APP processing, including α-, β-, and γ-secretases. Finally, we have highlighted the future perspectives pertaining to further research and the potential clinical role of APP.

The Brilliance of the Zebrafish Model: Perception on Behavior and Alzheimer's Disease

Alzheimer's disease (AD) has become increasingly prevalent in the elderly population across the world. It's pathophysiological markers such as overproduction along with the accumulation of amyloid beta (Aβ) plaques and neurofibrillary tangles (NFT) are posing a serious challenge to novel drug development processes. A model which simulates the human neurodegenerative mechanism will be beneficial for rapid screening of potential drug candidates. Due to the comparable neurological network with humans, zebrafish has emerged as a promising AD model. This model has been thoroughly validated through research in aspects of neuronal pathways analogous to the human brain. The cholinergic, glutamatergic, and GABAergic pathways, which play a role in the manifested behavior of the zebrafish, are well defined. There are several behavioral models in both adult zebrafish and larvae to establish various aspects of cognitive impairment including spatial memory, associative memory, anxiety, and other such features that are manifested in AD. The zebrafish model eliminates the shortcomings of previously recognized mammalian models, in terms of expense, extensive assessment durations, and the complexity of imaging the brain to test the efficacy of therapeutic interventions. This review highlights the various models that analyze the changes in the normal behavioral patterns of the zebrafish when exposed to AD inducing agents. The mechanistic pathway adopted by drugs and novel therapeutic strategies can be explored via these behavioral models and their efficacy to slow the progression of AD can be evaluated.

Presenilin enhancer 2 is crucial for the transition of apical progenitors into neurons but into not basal progenitors in the developing hippocampus

Recent evidence has shown that presenilin enhancer 2 (Pen2; Psenen) plays an essential role in corticogenesis by regulating the switch of apical progenitors (APs) to basal progenitors (BPs). The hippocampus is a brain structure required for advanced functions, including spatial navigation, learning and memory. However, it remains unknown whether Pen2 is important for hippocampal morphogenesis. To address this question, we generated Pen2 conditional knockout (cKO) mice, in which Pen2 is inactivated in neural progenitor cells (NPCs) in the hippocampal primordium. We showed that Pen2 cKO mice exhibited hippocampal malformation and decreased population of NPCs in the neuroepithelium of the hippocampus. We found that deletion of Pen2 neither affected the proliferative capability of APs nor the switch of APs to BPs in the hippocampus, and that it caused enhanced transition of APs to neurons. We demonstrated that expression of the Notch1 intracellular domain (N1ICD) significantly increased the population of NPCs in the Pen2 cKO hippocampus. Collectively, this study uncovers a crucial role for Pen2 in the maintenance of NPCs during hippocampal development.

γ-Secretase in Alzheimer's disease

Alzheimer's disease (AD) is caused by synaptic and neuronal loss in the brain. One of the characteristic hallmarks of AD is senile plaques containing amyloid β-peptide (Aβ). Aβ is produced from amyloid precursor protein (APP) by sequential proteolytic cleavages by β-secretase and γ-secretase, and the polymerization of Aβ into amyloid plaques is thought to be a key pathogenic event in AD. Since γ-secretase mediates the final cleavage that liberates Aβ, γ-secretase has been widely studied as a potential drug target for the treatment of AD. γ-Secretase is a transmembrane protein complex containing presenilin, nicastrin, Aph-1, and Pen-2, which are sufficient for γ-secretase activity. γ-Secretase cleaves >140 substrates, including APP and Notch. Previously, γ-secretase inhibitors (GSIs) were shown to cause side effects in clinical trials due to the inhibition of Notch signaling. Therefore, more specific regulation or modulation of γ-secretase is needed. In recent years, γ-secretase modulators (GSMs) have been developed. To modulate γ-secretase and to understand its complex biology, finding the binding sites of GSIs and GSMs on γ-secretase as well as identifying transiently binding γ-secretase modulatory proteins have been of great interest. In this review, decades of findings on γ-secretase in AD are discussed.

Evolutionary distinct roles of γ-secretase subunit nicastrin in zebrafish and humans

BACKGROUND

Mutations in the genes that encode the human γ-secretase subunits Presenilin-1, Presenilin Enhancer Protein 2, and Nicastrin (NCSTN) are associated with familial hidradenitis suppurativa (HS); and, regarding Presenilin Enhancer Protein 2, also with comorbidity for the hereditary pigmentation disorder Dowling-Degos disease.

OBJECTIVE

Here, the consequences of targeted inactivation of ncstn, the zebrafish homologue of human NCSTN, were studied.

METHODS

After morpholino (MO)-mediated ncstn-knockdown, the possibilities of phenotype rescue through co-injection of ncstn-MO with wildtype zebrafish ncstn or human NCSTN mRNA were investigated. Further, the effects of the co-injection of a human missense, nonsense, splice-site, and frameshift mutation were studied.

RESULTS

MO-mediated ncstn-knockdown resulted in a significant reduction in melanophore morphology, size and number; and alterations in their patterns of migration and distribution. This phenotype was rescued by co-injection of zebrafish ncstn RNA, human NCSTN RNA, or a construct encoding the human NCSTN missense mutation p.P211R.

CONCLUSION

Human NCSTN mutations encoding null alleles confer loss-of-function regarding pigmentation homeostasis in zebrafisch. In contrast, the human missense mutation p.P211R was less harmful, asserting sufficient residual ncstn activity to maintain pigmentation in zebrafish. Since fish lack the anatomical structures affected by HS, our data suggest that the zebrafish ncstn gene and the human NCSTN gene have probably acquired different functions during evolution. In fish, one major role of ncstn is the maintenance of pigmentation homeostasis. In contrast, one of the roles of NCSTN in humans is the prevention of inflammatory processes in the adnexal structures of the skin, as seen in familial HS.

Application and advantages of zebrafish model in the study of neurovascular unit

The concept of "Neurovascular Unit" (NVU) was put forward, so that the research goal of Central Nervous System (CNS) diseases gradually transitioned from a single neuron to the structural and functional integrity of the NVU. Zebrafish has the advantages of high homology with human genes, strong reproductive capacity and visualization of neural circuits, so it has become an emerging model organism for NVU research and has been applied to a variety of CNS diseases. Based on CNKI (https://www.cnki.net/) and PubMed (https://pubmed.ncbi.nlm.nih.gov/about/) databases, the author of this article sorted out the relevant literature, analyzed the construction of a zebrafish model of various CNS diseases，and the use of diagrams showed the application of zebrafish in the NVU, revealed its relationship, which would provide new methods and references for the treatment and research of CNS diseases.

The role of auditory and vibration stimuli in zebrafish neurobehavioral models

Strongly affecting human and animal physiology, sounds and vibration are critical environmental factors whose complex role in behavioral and brain functions necessitates further clinical and experimental studies. Zebrafish are a promising model organism for neuroscience research, including probing the contribution of auditory and vibration stimuli to neurobehavioral processes. Here, we summarize mounting evidence on the role of sound and vibration in zebrafish behavior and brain function, and outline future directions of translational research in this field. With the growing environmental exposure to noise and vibration, we call for more active use of zebrafish models for probing neurobehavioral and bioenvironmental consequences of acute and long-term exposure to sounds and vibration in complex biological systems.

Use of Zebrafish Genetic Models to Study Etiology of the Amyloid-Beta and Neurofibrillary Tangle Pathways in Alzheimer's Disease

The prevalence of neurodegenerative diseases is increasing globally, with an imperative need to identify and expand the availability of pharmaceutical treatment strategies. Alzheimer's disease is the most common neurodegenerative disease for which there is no cure or has limited treatments. Rodent models are primarily used in Alzheimer's disease research to investigate causes, pathology, molecular mechanisms, and pharmaceutical therapies. However, there is a lack of a comprehensive understanding of Alzheimer's disease causes, pathogenesis, and optimal treatments due in part to some limitations of using rodents, including higher economic cost, which can influence sample size and ultimately statistical power. It is necessary to expand our animal model toolbox to provide alternative strategies in Alzheimer's disease research. The zebrafish application in neurodegenerative disease research and neuropharmacology is greatly expanding due to several vital strengths spanning lower economic costs, the smaller size of the organism, a sequenced characterized genome, and well described anatomical structures. These characteristics are coupled to the conserved molecular function and disease pathways in humans. The existence of orthologs for genes associated with Alzheimer's disease in zebrafish is also confirmed. While wild-type zebrafish appear to lack some of the neuropathological features of Alzheimer's disease, the advent of genetic editing technologies has expanded evaluation of the amyloid and neurofibrillary tangle hypotheses using the zebrafish and exploration of pharmaceutical molecular targets. An overview of how genetic editing technologies are being used with the zebrafish to create models to investigate the causes, pathology, molecular mechanisms, and pharmaceutical targets of Alzheimer's disease is detailed.

Auditory environmental enrichment prevents anxiety-like behavior, but not cortisol responses, evoked by 24-h social isolation in zebrafish

The zebrafish (Danio rerio) is widely used as a promising translational model organism for studying various brain disorders. Zebrafish are also commonly used in behavioral and drug screening assays utilizing individually tested (socially isolated) fish. Various sounds represent important exogenous factors that may affect fish behavior. Mounting evidence shows that musical/auditory environmental enrichment can improve welfare of laboratory animals, including fishes. Here, we show that auditory environmental enrichment mitigates anxiogenic-like effects caused by acute 24-h social isolation in adult zebrafish. Thus, auditory environmental enrichment may offer an inexpensive, feasible and simple tool to improve welfare of zebrafish stocks in laboratory facilities, reduce unwanted procedural stress, lower non-specific behavioral variance and, hence, collectively improve zebrafish data reliability and reproducibility.

Using zebrafish (Danio rerio) models to understand the critical role of social interactions in mental health and wellbeing

Social behavior represents a beneficial interaction between conspecifics that is critical for maintaining health and wellbeing. Dysfunctional or poor social interaction are associated with increased risk of physical (e.g., vascular) and psychiatric disorders (e.g., anxiety, depression, and substance abuse). Although the impact of negative and positive social interactions is well-studied, their underlying mechanisms remain poorly understood. Zebrafish have well-characterized social behavior phenotypes, high genetic homology with humans, relative experimental simplicity and the potential for high-throughput screens. Here, we discuss the use of zebrafish as a candidate model organism for studying the fundamental mechanisms underlying social interactions, as well as potential impacts of social isolation on human health and wellbeing. Overall, the growing utility of zebrafish models may improve our understanding of how the presence and absence of social interactions can differentially modulate various molecular and physiological biomarkers, as well as a wide range of other behaviors.

Caenorhabditis elegans Models to Investigate the Mechanisms Underlying Tau Toxicity in Tauopathies

The understanding of the genetic, biochemical, and structural determinants underlying tau aggregation is pivotal in the elucidation of the pathogenic process driving tauopathies and the design of effective therapies. Relevant information on the molecular basis of human neurodegeneration in vivo can be obtained using the nematode Caenorhabditis elegans (C. elegans). To this end, two main approaches can be applied: the overexpression of genes/proteins leading to neuronal dysfunction and death, and studies in which proteins prone to misfolding are exogenously administered to induce a neurotoxic phenotype. Thanks to the easy generation of transgenic strains expressing human disease genes, C. elegans allows the identification of genes and/or proteins specifically associated with pathology and the specific disruptions of cellular processes involved in disease. Several transgenic strains expressing human wild-type or mutated tau have been developed and offer significant information concerning whether transgene expression regulates protein production and aggregation in soluble or insoluble form, onset of the disease, and the degenerative process. C. elegans is able to specifically react to the toxic assemblies of tau, thus developing a neurodegenerative phenotype that, even when exogenously administered, opens up the use of this assay to investigate in vivo the relationship between the tau sequence, its folding, and its proteotoxicity. These approaches can be employed to screen drugs and small molecules that can interact with the biogenesis and dynamics of formation of tau aggregates and to analyze their interactions with other cellular proteins.

Neuron-specific deletion of presenilin enhancer2 causes progressive astrogliosis and age-related neurodegeneration in the cortex independent of the Notch signaling

Introduction

Presenilin enhancer2 (Pen‐2) is an essential subunit of γ‐secretase, which is a key protease responsible for the cleavage of amyloid precursor protein (APP) and Notch. Mutations on Pen‐2 cause familial Alzheimer disease (AD). However, it remains unknown whether Pen‐2 regulates neuronal survival and neuroinflammation in the adult brain.

Methods

Forebrain neuron‐specific Pen‐2 conditional knockout (Pen‐2 cKO) mice were generated for this study. Pen‐2 cKO mice expressing Notch1 intracellular domain (NICD) conditionally in cortical neurons were also generated.

Results

Loss of Pen‐2 causes astrogliosis followed by age‐dependent cortical atrophy and neuronal loss. Loss of Pen‐2 results in microgliosis and enhanced inflammatory responses in the cortex. Expression of NICD in Pen‐2 cKO cortices ameliorates neither neurodegeneration nor neuroinflammation.

Conclusions

Pen‐2 is required for neuronal survival in the adult cerebral cortex. The Notch signaling may not be involved in neurodegeneration caused by loss of Pen‐2.

Neuroinflammation: An overview of neurodegenerative and metabolic diseases and of biotechnological studies

Neuroinflammation is an important factor contributing to cognitive impairment and neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic lateral sclerosis (ALS), ischemic injury, and multiple sclerosis (MS). These diseases are characterized by inexorable progressive injury of neuron cells, and loss of motor or cognitive functions. Microglia, which are the resident macrophages in the brain, play an important role in both physiological and pathological conditions. In this review, we provide an updated discussion on the role of ROS and metabolic disease in the pathological mechanisms of activation of the microglial cells and release of cytotoxins, leading to the neurodegenerative process. In addition, we also discuss in vivo models, such as zebrafish and Caenorhabditis elegans, and provide new insights into therapeutics bioinspired by neuropeptides from venomous animals, supporting high throughput drug screening in the near future, searching for a complementary approach to elucidating crucial mechanisms associated with neurodegenerative disorders.

Swimming in Deep Water: Zebrafish Modeling of Complicated Forms of Hereditary Spastic Paraplegia and Spastic Ataxia

Hereditary spastic paraplegia (HSP) and hereditary ataxia (HA) are two groups of disorders characterized, respectively, by progressive dysfunction or degeneration of the pyramidal tracts (HSP) and of the Purkinje cells and spinocerebellar tracts (HA). Although HSP and HA are generally shown to have distinct clinical-genetic profiles, in several cases the clinical presentation, the causative genes, and the cellular pathways and mechanisms involved overlap between the two forms. Genetic analyses in humans in combination with in vitro and in vivo studies using model systems have greatly expanded our knowledge of spinocerebellar degenerative disorders. In this review, we focus on the zebrafish (Danio rerio), a vertebrate model widely used in biomedical research since its overall nervous system organization is similar to that of humans. A critical analysis of the literature suggests that zebrafish could serve as a powerful experimental tool for molecular and genetic dissection of both HA and HSP. The zebrafish, found to be very useful for demonstrating the causal relationship between defect and mutation, also offers a useful platform to exploit for the development of therapies.

Zebrafish as an Emerging Model for Bioassay-Guided Natural Product Drug Discovery for Neurological Disorders

Most neurodegenerative diseases are currently incurable, with large social and economic impacts. Recently, there has been renewed interest in investigating natural products in the modern drug discovery paradigm as novel, bioactive small molecules. Moreover, the discovery of potential therapies for neurological disorders is challenging and involves developing optimized animal models for drug screening. In contemporary biomedicine, the growing need to develop experimental models to obtain a detailed understanding of malady conditions and to portray pioneering treatments has resulted in the application of zebrafish to close the gap between in vitro and in vivo assays. Zebrafish in pharmacogenetics and neuropharmacology are rapidly becoming a widely used organism. Brain function, dysfunction, genetic, and pharmacological modulation considerations are enhanced by both larval and adult zebrafish. Bioassay-guided identification of natural products using zebrafish presents as an attractive strategy for generating new lead compounds. Here, we see evidence that the zebrafish's central nervous system is suitable for modeling human neurological disease and we review and evaluate natural product research using zebrafish as a vertebrate model platform to systematically identify bioactive natural products. Finally, we review recently developed zebrafish models of neurological disorders that have the potential to be applied in this field of research.

γ-Secretase and its modulators: Twenty years and beyond

Twenty years ago, Wolfe, Xia, and Selkoe identified two aspartate residues in Alzheimer's presenilin protein that constitute the active site of the γ-secretase complex. Mutations in the genes encoding amyloid precursor protein (APP) or presenilin (PS) cause early onset familial Alzheimer's disease (AD), and sequential cleavages of the APP by β-secretase and γ-secretase/presenilin generate amyloid β protein (Aβ), the major component of pathological hallmark, neuritic plaques, in brains of AD patients. Therapeutic strategies centered on targeting γ-secretase/presenilin to reduce amyloid were implemented and led to several high profile clinical trials. This review article focuses on the studies of γ-secretase and its inhibitors/modulators since the discovery of presenilin as the γ-secretase. While a lack of complete understanding of presenilin biology renders failure of clinical trials, the lessons learned from some γ-secretase modulators, while premature for human testing, provide new directions to develop potential therapeutics. Imbalanced Aβ homeostasis is an upstream event of neurodegenerative processes. Exploration of γ-secretase modulators for their roles in these processes is highly significant, e.g., decreasing neuroinflammation and levels of phosphorylated tau, the component of the other AD pathological hallmark, neurofibrillary tangles. Agents with excellent human pharmacology hold great promise in suppressing neurodegeneration in pre-symptomatic or early stage AD patients.

Zebrafish: an emerging real-time model system to study Alzheimer's disease and neurospecific drug discovery

Zebrafish (Danio rerio) is emerging as an increasingly successful model for translational research on human neurological disorders. In this review, we appraise the high degree of neurological and behavioural resemblance of zebrafish with humans. It is highly validated as a powerful vertebrate model for investigating human neurodegenerative diseases. The neuroanatomic and neurochemical pathways of zebrafish brain exhibit a profound resemblance with the human brain. Physiological, emotional and social behavioural pattern similarities between them have also been well established. Interestingly, zebrafish models have been used successfully to simulate the pathology of Alzheimer’s disease (AD) as well as Tauopathy. Their relatively simple nervous system and the optical transparency of the embryos permit real-time neurological imaging. Here, we further elaborate on the use of recent real-time imaging techniques to obtain vital insights into the neurodegeneration that occurs in AD. Zebrafish is adeptly suitable for Ca²⁺ imaging, which provides a better understanding of neuronal activity and axonal dystrophy in a non-invasive manner. Three-dimensional imaging in zebrafish is a rapidly evolving technique, which allows the visualisation of the whole organism for an elaborate in vivo functional and neurophysiological analysis in disease condition. Suitability to high-throughput screening and similarity with humans makes zebrafish an excellent model for screening neurospecific compounds. Thus, the zebrafish model can be pivotal in bridging the gap from the bench to the bedside. This fish is becoming an increasingly successful model to understand AD with further scope for investigation in neurodevelopment and neurodegeneration, which promises exciting research opportunities in the future.

Lower vertebrate and invertebrate models of Alzheimer's disease - A review

Alzheimer's disease is a common neurodegenerative disorder which is characterized by the presence of beta- amyloid protein and neurofibrillary tangles (NFTs) in the brain. Till now, various higher vertebrate models have been in use to study the pathophysiology of this disease. But, these models possess some limitations like ethical restrictions, high cost, difficult maintenance of large quantity and lesser reproducibility. Besides, various lower chordate animals like Danio rerio, Drosophila melanogaster, Caenorhabditis elegans and Ciona intestinalis have been proved to be an important model for the in vivo determination of targets of drugs with least limitations. In this article, we reviewed different studies conducted on theses models for the better understanding of the pathophysiology of AD and their subsequent application as a potential tool in the preclinical evaluation of new drugs.

Understanding taurine CNS activity using alternative zebrafish models

Taurine is a highly abundant "amino acid" in the brain. Despite the potential neuroactive role of taurine in vertebrates has long been recognized, the underlying molecular mechanisms related to its pleiotropic effects in the brain remain poorly understood. Due to the genetic tractability, rich behavioral repertoire, neurochemical conservation, and small size, the zebrafish (Danio rerio) has emerged as a powerful candidate for neuropsychopharmacology investigation and in vivo drug screening. Here, we summarize the main physiological roles of taurine in mammals, including neuromodulation, osmoregulation, membrane stabilization, and antioxidant action. In this context, we also highlight how zebrafish models of brain disorders may present interesting approaches to assess molecular mechanisms underlying positive effects of taurine in the brain. Finally, we outline recent advances in zebrafish drug screening that significantly improve neuropsychiatric translational researches and small molecule screens.

P53 Dysfunction in Neurodegenerative Diseases - The Cause or Effect of Pathological Changes?

Neurodegenerative diseases are a heterogeneous, mostly age-associated group of disorders characterized by progressive neuronal loss, the most prevalent being Alzheimer disease. It is anticipated that, with continuously increasing life expectancy, these diseases will pose a serious social and health problem in the near feature. Meanwhile, however, their etiology remains largely obscure even though all possible novel clues are being thoroughly examined. In this regard, a concept has been proposed that p53, as a transcription factor controlling many vital cellular pathways including apoptosis, may contribute to neuronal death common to all neurodegenerative disorders. In this work, we review the research devoted to the possible role of p53 in the pathogenesis of these diseases. We not only describe aberrant changes in p53 level/activity observed in CNS regions affected by particular diseases but, most importantly, put special attention to the complicated reciprocal regulatory ties existing between p53 and proteins commonly regarded as pathological hallmarks of these diseases, with the ultimate goal to identify the primary element of their pathogenesis.

Zebrafish models in neuropsychopharmacology and CNS drug discovery

Despite the high prevalence of neuropsychiatric disorders, their aetiology and molecular mechanisms remain poorly understood. The zebrafish (Danio rerio) is increasingly utilized as a powerful animal model in neuropharmacology research and in vivo drug screening. Collectively, this makes zebrafish a useful tool for drug discovery and the identification of disordered molecular pathways. Here, we discuss zebrafish models of selected human neuropsychiatric disorders and drug-induced phenotypes. As well as covering a broad range of brain disorders (from anxiety and psychoses to neurodegeneration), we also summarize recent developments in zebrafish genetics and small molecule screening, which markedly enhance the disease modelling and the discovery of novel drug targets.

Presenilin-1 Targeted Morpholino Induces Cognitive Deficits, Increased Brain Aβ1-42 and Decreased Synaptic Marker PSD-95 in Zebrafish Larvae

Presenilins are transmembrane proteases required for the proteolytic cleavage of Notch and also act as the catalytic core of the γ-secretase complex, which is responsible for the final cleavage of the amyloid precursor protein into Amyloid-β (Aβ) peptides of varying lengths. Presenilin-1 gene (psen1) mutations are the main cause of early-onset autosomal-dominant Familial Alzheimer Disease. Elucidating the roles of Presenilin-1 and other hallmark proteins involved in Alzheimer's disease is crucial for understanding the disease etiology and underlying molecular mechanisms. In our study, we used a morpholino antisense nucleotide that targets exon 8 splicing site of psen1 resulting in a dominant negative protein previously validated to investigate behavioral and molecular effects in 5 days post fertilization (dpf) zebrafish larvae. Morphants showed specific cognitive deficits in two optomotor tasks and morphological phenotypes similar to those induced by suppression of Notch signaling pathway. They also had increased mRNA levels of neurog1 at 5 dpf, confirming the potential interaction of Presenilin-1 and Notch in our model. We also evaluated levels of apoptotic markers including p53, PAR-4, Caspase-8 and bax-alpha and found only bax-a decreased at 5dpf. Western Blot analysis showed an increase in Aβ_1-42 and a decrease in the selective post-synaptic marker PSD-95 at 5 dpf. Our data demonstrates that psen1 splicing interference induces phenotypes that resemble early-stage AD, including cognitive deficit, Aβ_1-42 accumulation and synaptic reduction, reinforcing the potential contribution of zebrafish larvae to studies of human brain diseases.

Propylthiouracil Attenuates Experimental Pulmonary Hypertension via Suppression of Pen-2, a Key Component of Gamma-Secretase

Gamma-secretase-mediated Notch3 signaling is involved in smooth muscle cell (SMC) hyper-activity and proliferation leading to pulmonary arterial hypertension (PAH). In addition, Propylthiouracil (PTU), beyond its anti-thyroid action, has suppressive effects on atherosclerosis and PAH. Here, we investigated the possible involvement of gamma-secretase-mediated Notch3 signaling in PTU-inhibited PAH. In rats with monocrotaline-induced PAH, PTU therapy improved pulmonary arterial hypertrophy and hemodynamics. In vitro, treatment of PASMCs from monocrotaline-treated rats with PTU inhibited their proliferation and migration. Immunocyto, histochemistry, and western blot showed that PTU treatment attenuated the activation of Notch3 signaling in PASMCs from monocrotaline-treated rats, which was mediated via inhibition of gamma-secretase expression especially its presenilin enhancer 2 (Pen-2) subunit. Furthermore, over-expression of Pen-2 in PASMCs from control rats increased the capacity of migration, whereas knockdown of Pen-2 with its respective siRNA in PASMCs from monocrotaline-treated rats had an opposite effect. Transfection of PASMCs from monocrotaline-treated rats with Pen-2 siRNA blocked the inhibitory effect of PTU on PASMC proliferation and migration, reflecting the crucial role of Pen-2 in PTU effect. We present a novel cell-signaling paradigm in which overexpression of Pen-2 is essential for experimental pulmonary arterial hypertension to promote motility and growth of smooth muscle cells. Propylthiouracil attenuates experimental PAH via suppression of the gamma-secretase-mediated Notch3 signaling especially its presenilin enhancer 2 (Pen-2) subunit. These findings provide a deep insight into the pathogenesis of PAH and a novel therapeutic strategy.

Tetracapsuloides bryosalmonae infection affects the expression of genes involved in cellular signal transduction and iron metabolism in the kidney of the brown trout Salmo trutta

Tetracapsuloides bryosalmonae is an enigmatic endoparasite which causes proliferative kidney disease in various species of salmonids in Europe and North America. The life cycle of the European strain of T. bryosalmonae generally completes in an invertebrate host freshwater bryozoan and vertebrate host brown trout (Salmo trutta) Linnaeus, 1758. Little is known about the gene expression in the kidney of brown trout during the developmental stages of T. bryosalmonae. In the present study, quantitative real-time PCR was applied to quantify the target genes of interest in the kidney of brown trout at different time points of T. bryosalmonae development. PCR primers specific for target genes were designed and optimized, and their gene expression levels were quantified in the cDNA kidney samples using SYBR Green Supermix. Expression of Rab GDP dissociation inhibitor beta, integral membrane protein 2B, NADH dehydrogenase 1 beta subcomplex subunit 6, and 26S protease regulatory subunit S10B were upregulated significantly in infected brown trout, while the expression of the ferritin M middle subunit was downregulated significantly. These results suggest that host genes involved in cellular signal transduction, proteasomal activities, including membrane transporters and cellular iron storage, are differentially upregulated or downregulated in the kidney of brown trout during parasite development. The gene expression pattern of infected renal tissue may support the development of intraluminal sporogonic stages of T. bryosalmonae in the renal tubular lumen of brown trout which may facilitate the release of viable parasite spores to transmit to the invertebrate host bryozoan.

All-trans-retinoic acid inhibits chondrogenesis of rat embryo hindlimb bud mesenchymal cells by downregulating p53 expression

Despite the well-established role of all-trans-retinoic acid (ATRA) in congenital clubfoot (CCF)-like deformities in in vivo models, the essential cellular and molecular targets and the signaling mechanisms for ATRA-induced CCF-like deformities remain to be elucidated. Recent studies have demonstrated that p53 and p21, expressed in the hindlimb bud mesenchyme, regulate cellular proliferation and differentiation, contributing to a significant proportion of embryonic CCF-like abnormalities. The objective of the present study was to investigate the mechanisms for ATRA-induced CCF, by assessing ATRA-regulated chondrogenesis in rat embryo hindlimb bud mesenchymal cells (rEHBMCs) in vitro. The experimental study was based on varying concentrations of ATRA exposure on embryonic day 12.5 rEHBMCs in vitro. The present study demonstrated that ATRA inhibited the proliferation of cells by stimulating apoptotic cell death of rEHBMCs. It was also observed that ATRA induced a dose-dependent reduction of cartilage nodules compared with the control group. Reverse transcription-polymerase chain reaction and western blotting assays revealed that the mRNA and protein expression of cartilage-specific molecules, including aggrecan, Sox9 and collagen, type II, α 1 (Col2a1), were downregulated by ATRA in a dose-dependent manner; the mRNA levels of p53 and p21 were dose-dependently upregulated from 16 to 20 h of incubation with ATRA, but dose-dependently downregulated from 24 to 48 h. Of note, p53 and p21 were regulated at the translational level in parallel with the transcription with rEHBMCs treated with ATRA. Furthermore, the immunofluorescent microscopy assays indicated that proteins of p53 and p21 were predominantly expressed in the cartilage nodules. The present study demonstrated that ATRA decreases the chondrogenesis of rEHBMCs by inhibiting cartilage-specific molecules, including aggrecan, Sox9 and Col2al, via regulating the expression of p53 and p21.

Using the zebrafish model for Alzheimer's disease research

Rodent models have been extensively used to investigate the cause and mechanisms behind Alzheimer’s disease. Despite many years of intensive research using these models we still lack a detailed understanding of the molecular events that lead to neurodegeneration. Although zebrafish lack the complexity of advanced cognitive behaviors evident in rodent models they have proven to be a very informative model for the study of human diseases. In this review we give an overview of how the zebrafish has been used to study Alzheimer’s disease. Zebrafish possess genes orthologous to those mutated in familial Alzheimer’s disease and research using zebrafish has revealed unique characteristics of these genes that have been difficult to observe in rodent models. The zebrafish is becoming an increasingly popular model for the investigation of Alzheimer’s disease and will complement studies using other models to help complete our understanding of this disease.

Zebrafish brain lipid characterization and quantification by ¹H nuclear magnetic resonance spectroscopy and MALDI-TOF mass spectrometry

Lipids play an important role in many neurodegenerative diseases, such as Parkinson's disease, Alzheimer's disease, and Huntington's disease. Zebrafish models for these diseases have been recently developed. The detailed brain lipid composition of the adult zebrafish is not known, and therefore, the representativeness of these models cannot be properly evaluated. In this study, we characterized the total lipid composition of healthy adult zebrafish using (1)H nuclear magnetic resonance spectroscopy. A close resemblance of the zebrafish brain composition is shown in comparison to the human brain. Moreover, several lipids involved in the pathogenesis of neurodegenerative diseases (i.e., cholesterol, phosphatidylcholine, docosahexaenoic acid, and further, polyunsaturated fatty acids) are detected and quantified. These lipids might represent useful biomarkers in future research toward human therapies. Matrix-assisted laser desorption-ionization time-of-flight mass spectrometry coupled with high-performance thin-layer chromatography was used for further characterization of zebrafish brain lipids. Our results show that the lipid composition of the zebrafish brain is rather similar to the human brain and thus confirms that zebrafish represents a good model for studying various brain diseases.

SiO2 nanoparticles change colour preference and cause Parkinson's-like behaviour in zebrafish

With advances in the development of various disciplines, there is a need to decipher bio-behavioural mechanisms via interdisciplinary means. Here, we present an interdisciplinary study of the role of silica nanoparticles (SiO2-NPs) in disturbing the neural behaviours of zebrafish and a possible physiological mechanism for this phenomenon. We used adult zebrafish as an animal model to evaluate the roles of size (15-nm and 50-nm) and concentration (300 μg/mL and 1000 μg/mL) in SiO2-NP neurotoxicity via behavioural and physiological analyses. With the aid of video tracking and data mining, we detected changes in behavioural phenotypes. We found that compared with 50-nm nanosilica, 15-nm SiO2-NPs produced greater significant changes in advanced cognitive neurobehavioural patterns (colour preference) and caused potentially Parkinson's disease-like behaviour. Analyses at the tissue, cell and molecular levels corroborated the behavioural results, demonstrating that nanosilica acted on the retina and dopaminergic (DA) neurons to change colour preference and to cause potentially Parkinson's disease-like behaviour.

p53 in neurodegenerative diseases and brain cancers

More than thirty years elapsed since a protein, not yet called p53 at the time, was detected to bind SV40 during viral infection. Thousands of papers later, p53 evolved as the main tumor suppressor involved in growth arrest and apoptosis. A lot has been done but the protein has not yet revealed all its secrets. Particularly important is the observation that in totally distinct pathologies where apoptosis is either exacerbated or impaired, p53 appears to play a central role. This is exemplified for Alzheimer's and Parkinson's diseases that represent the two main causes of age-related neurodegenerative affections, where cell death enhancement appears as one of the main etiological paradigms. Conversely, in cancers, about half of the cases are linked to mutations in p53 leading to the impairment of p53-dependent apoptosis. The involvement of p53 in these pathologies has driven a huge amount of studies aimed at designing chemical tools or biological approaches to rescue p53 defects or over-activity. Here, we describe the data linking p53 to neurodegenerative diseases and brain cancers, and we document the various strategies to interfere with p53 dysfunctions in these disorders.

Enzymatic GST levels and overall health of mullets from contaminated Brazilian Lagoons

Glutathione S-transferase (GST) assays in non-mammalian organisms are usually conducted inappropriately, since no previous standardization of the optimal concentrations of proteins and substrates and adequate pH is conducted. Standardization is a key task to adjust enzyme assays at their kinetically correct maximal initial velocities, if one wants these velocities to indicate the amount of enzyme in a sample. In this paper GST assays were standardized in liver cytosol to compare seasonal GST levels in liver of mullet from two contaminated lagoons in the Rio de Janeiro to those from a reference bay. GST potential as a biomarker of sublethal intoxication in this species was also evaluated. Mullet liver GST levels assayed with substrates that corresponded to three different GST isoenzymes varied throughout the year. The differences indicated that mullets are suffering from sublethal intoxication from contaminants in these lagoons. Seasonal variations of activity were relevant, since these could indicate differences in xenobiotic input into the areas. An analysis of overall mullet health condition using a morphological index (the Fulton Condition Factor) and macroscopic abnormalities corroborated the differences in GST levels, with fish from one of the sites in worse overall health condition showing lower and significantly different FCF when compared to the reference site. Therefore, GST standardized activity levels are useful biomarkers of environmental contamination for mullet.

Computational techniques in zebrafish image processing and analysis

The zebrafish (Danio rerio) has been widely used as a vertebrate animal model in neurobiological. The zebrafish has several unique advantages that make it well suited for live microscopic imaging, including its fast development, large transparent embryos that develop outside the mother, and the availability of a large selection of mutant strains. As the genome of zebrafish has been fully sequenced it is comparatively easier to carry out large scale forward genetic screening in zebrafish to investigate relevant human diseases, from neurological disorders like epilepsy, Alzheimer's disease, and Parkinson's disease to other conditions, such as polycystic kidney disease and cancer. All of these factors contribute to an increasing number of microscopic images of zebrafish that require advanced image processing methods to objectively, quantitatively, and quickly analyze the image dataset. In this review, we discuss the development of image analysis and quantification techniques as applied to zebrafish images, with the emphasis on phenotype evaluation, neuronal structure quantification, vascular structure reconstruction, and behavioral monitoring. Zebrafish image analysis is continually developing, and new types of images generated from a wide variety of biological experiments provide the dataset and foundation for the future development of image processing algorithms.