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BACKGROUND: Cortical microinfarcts (CMI) were attributed to cerebrovascular disease and cerebral amyloid angiopathy (CAA). CAA is frequent in Down syndrome (DS) while hypertension is rare, yet no studies have assessed CMI in DS. METHODS: We included 195 adults with DS, 63 with symptomatic sporadic Alzheimer's disease (AD), and 106 controls with 3T magnetic resonance imaging. We assessed CMI prevalence in each group and CMI association with age, AD clinical continuum, vascular risk factors, vascular neuroimaging findings, amyloid/tau/neurodegeneration biomarkers, and cognition in DS. RESULTS: CMI prevalence was 11.8% in DS, 4.7% in controls, and 17.5% in sporadic AD. In DS, CMI increased in prevalence with age and the AD clinical continuum, was clustered in the parietal lobes, and was associated with lacunes and cortico‐subcortical infarcts, but not hemorrhagic lesions. DISCUSSION: In DS, CMI are posteriorly distributed and related to ischemic but not hemorrhagic findings suggesting they might be associated with a specific ischemic CAA phenotype. Highlights: This is the first study to assess cortical microinfarcts (assessed with 3T magnetic resonance imaging) in adults with Down syndrome (DS).We studied the prevalence of cortical microinfarcts in DS and its relationship with age, the Alzheimer's disease (AD) clinical continuum, vascular risk factors, vascular neuroimaging findings, amyloid/tau/neurodegeneration biomarkers, and cognition.The prevalence of cortical microinfarcts was 11.8% in DS and increased with age and along the AD clinical continuum. Cortical microinfarcts were clustered in the parietal lobes, and were associated with lacunes and cortico‐subcortical infarcts, but not hemorrhagic lesions.In DS, cortical microinfarcts are posteriorly distributed and related to ischemic but not hemorrhagic findings suggesting they might be associated with a specific ischemic phenotype of cerebral amyloid angiopathy. [ABSTRACT FROM AUTHOR]

Gravity is one of the most constant environmental factors across Earth's evolution and all organisms are adapted to it. Consequently, spatial exploration has captured the interest in studying the biological changes that physiological alterations are caused by gravity. In the last two decades, epigenetics has explained how environmental cues can alter gene functions in organisms. Although many studies addressed gravity, the underlying biological and molecular mechanisms that occur in altered gravity for those epigenetics-related mechanisms, are mostly inexistent. The present study addressed the effects of hypergravity on development, behavior, gene expression, and most importantly, on the epigenetic changes in a worldwide animal model, the zebrafish (Danio rerio). To perform hypergravity experiments, a custom-centrifuge simulating the large diameter centrifuge (100 rpm ~ 3 g) was designed and zebrafish embryos were exposed during 5 days post fertilization (dpf). Results showed a significant decrease in survival at 2 dpf but no significance in the hatching rate. Physiological and morphological alterations including fish position, movement frequency, and swimming behavior showed significant changes due to hypergravity. Epigenetic studies showed significant hypermethylation of the genome of the zebrafish larvae subjected to 5 days of hypergravity. Downregulation of the gene expression of three epigenetic-related genes (dnmt1, dnmt3, and tet1), although not significant, was further observed. Taken altogether, gravity alterations affected biological responses including epigenetics in fish, providing a valuable roadmap of the putative hazards of living beyond Earth. [ABSTRACT FROM AUTHOR]

Background: Due to the triplication of the APP gene on chromosome 21, virtually all individuals with Down's syndrome (DS) present AD neuropathological hallmarks by the age of 40, and have a lifetime risk of developing dementia >90%. However, whether DS follows a stereotypical pattern of AD atrophy has not been investigated. Here, we aimed at defining the sequential grey matter (GM) volume loss across the whole AD continuum in adults with DS. Method: Cross‐sectional design. 248 adults with DS (n = 145 asymptomatic [preclinical], n = 93 prodromal/demented AD) and 181 euploid cognitively unimpaired (CU) individuals from the Down Alzheimer Barcelona Neuroimaging Initiative underwent a 3T‐MRI protocol (Table.1). T1‐weighted images were preprocessed using CAT12. GM volumes adjusted for demographics (age, sex) and nuisance variables (TIV, MRI scanner) were computed for each cortical region of the Hammer Atlas and for each DS participant, using the CU group as a reference. Adjusted volumes (W‐scores) were binarized using a threshold of ‐2.33 (corresponding to a regional volume <99th percentiles of the CU group) to examine the brain regions most frequently atrophied in DS compared to CU. Conditional probability analyses were additionally performed in DS to assess if a brain region was more likely to present with atrophy than another. Result: Adults with DS most frequently showed atrophy in the medial temporal lobe, anterior cingulate, and temporo‐parietal regions. This pattern remains essentially similar when using a dynamic range of thresholds (Fig1.A) and across clinical AD stages (Fig1.B), even though the proportion of individuals showing atrophy increased with disease progression (Fig1.C). Interestingly, the anterior cingulate was the most frequently atrophied region in asymptomatic but not prodromal/demented DS. Conditional probability analyses revealed that the hippocampus, amygdala, and anterior cingulate have a significantly higher probability of showing GM loss before any other regions. A second cluster of tempo‐parietal regions appears more likely to show atrophy than most other regions. Conclusion: In DS, GM atrophy appears to follow a stereotypical pattern that strongly resembles the one of sporadic AD. Brain developmental specificities (e.g., anterior cingulate) are coupled with AD‐like atrophy early in the disease and become less predominant with AD progression. [ABSTRACT FROM AUTHOR]

Background: With the development of amyloid‐modifying therapeutic agents that can lead to cerebral microhaemorrhages, it is critical to meticulously characterise the natural history of cerebral microbleeds (MBs) in populations genetically predisposed to develop Alzheimer's disease (AD), such as Down syndrome (DS). We aimed to investigate MB prevalence in a large cohort of adults with DS and define associations with demographic, genetic, fluid and imaging biomarkers of AD, and cognitive performance. Methods: Cross‐sectional design. Adults with DS and euploid controls from the Down Alzheimer Barcelona Neuroimaging Initiative underwent a 3T‐MRI protocol, including susceptibility‐weighted imaging (SWI) acquisition. Manual tracing of MBs was performed by two independent raters using ITK‐SNAP. Participants were classified according to MB status (MB‐/MB+) and severity (0, 1, 2+ MBs). Non‐parametric statistical tests were used to assess the effect of MBs on demographic, clinical, genetic, CSF and neuroimaging AD biomarkers, and cognitive tests. Results: We included 247 participants with DS along the AD continuum, and 167 euploid controls (Table 1). The proportion of MB+ was higher in DS participants than controls, and progressively increased with AD clinical stages and age in the DS group (Fig. 1). By contrast, MB status did not differ by APOEε4 status, intellectual disability, or sex. In DS, the MB+ group had increased white matter hyperintensity volume and decreased hippocampal volumes compared to MB‐. DS MB+ also had lower CSF Aβ42/40 ratio, higher CSF t‐tau and p‐tau‐181 concentrations, and tended toward worse cognitive performance. Most effects gradually evolved with MB severity, although significant differences were mainly between MB‐ vs MB 2+ (Fig. 2). Finally, sensitivity analyses showed that most results became non‐significant when comparing DS MB+ to a 1:1 DS MB‐ group matched for age, sex, intellectual disability and/or AD diagnosis. Conclusion: MB presence and severity are increased in adults with DS, and worsen with clinical progression and AD pathology. Yet, matched group analyses suggest that MB have limited impact on cognition and neurodegeneration. These results provide better characterisation of the presence and effect of MB in a population with an ultra‐high risk of developing AD who could benefit from new disease modifying drugs. [ABSTRACT FROM AUTHOR]

Background: Down's syndrome (DS) is a genetically determined form of Alzheimer's disease (AD). Typically not complicated by systemic vascular risk factors, the DS population represents a unique opportunity to unravel the complex relationship between AD and cerebrovascular disease. Here, we aim at studying the evolution over time of white matter hyperintensities (WMHs), a key hallmark of cerebrovascular disease frequently found in AD, and to assess their topographical progression and associations with AD biomarkers in adults with DS. Method: This longitudinal study included 43 DS adults (age = 39.8±10.4y; females = 41.9%; n = 37 asymptomatic AD, n = 6 symptomatic AD) and 81 euploid controls (age = 53.7±6.2y; females = 67.3%) from the Down‐Alzheimer Barcelona Neuroimaging Initiative, with at least 2 MRI visits with T1 and FLAIR acquisitions (time delay = 3.4±1.6y). WMHs were segmented using the Lesion Prediction Algorithm implemented in the Lesion Segmentation Toolbox (SPM12). WMH volumes were extracted in 36 regions of interest and used to compute total and regional annual volume changes. Non‐parametric statistical tests were performed to assess the effect of disease severity on WMH volume changes over time and define associations between longitudinal WMHs and baseline demographic and genetic data, and fluid biomarkers. Result: Total annual WMH volume change increased in symptomatic DS compared to both asymptomatic DS and controls (Figure 1A). Regionally, WMH load increased in regions showing WMH at baseline in all groups (Figure 2). These changes were greater and more distributed, involving layers more distant from the ventricles (especially in occipito‐parietal regions) in symptomatic DS. Age, but not sex, intellectual disability, or APOEε4 status, was associated with longitudinal WMH in DS (Figure 1B‐F): the annual WMH volume changes in DS differed from controls at age ∼45y. Finally, WMH volume changes were negatively related to CSF‐Aβ42/40 and positively related to plasma and CSF ptau‐181 and neurofilament light (Figure 3). Conclusion: Pathological increases in WMH volume start ∼10 years before the mean age at onset for AD (53.8y) in DS and relate to underlying AD pathology and neurodegeneration. Regional analyses suggest that WMH volume changes increase with disease progression and progressively involve deeper white matter areas. Together, these results support that WMHs are tightly related to AD pathogenesis. [ABSTRACT FROM AUTHOR]

Background: Basal forebrain (BF) degeneration occurs in Down syndrome (DS)‐associated Alzheimer's disease (AD). However, the dynamics of BF atrophy with age and disease progression, its impact on cognition, and its relationship with AD biomarkers have not been studied in DS. Methods: We included 234 adults with DS (150 asymptomatic, 38 prodromal AD, and 46 AD dementia) and 147 euploid controls. BF volumes were extracted from T‐weighted magnetic resonance images using a stereotactic atlas in SPM12. We assessed BF volume changes with age and along the clinical AD continuum and their relationship to cognitive performance, cerebrospinal fluid (CSF) and plasma amyloid/tau/neurodegeneration biomarkers, and hippocampal volume. Results: In DS, BF volumes decreased with age and along the clinical AD continuum and significantly correlated with amyloid, tau, and neurofilament light chain changes in CSF and plasma, hippocampal volume, and cognitive performance. Discussion: BF atrophy is a potentially valuable neuroimaging biomarker of AD‐related cholinergic neurodegeneration in DS. [ABSTRACT FROM AUTHOR]

Rearing density directly impacts fish welfare, which, in turn, affects productivity in aquaculture. Previous studies have indicated that high-density rearing during sexual development in fish can induce stress, resulting in a tendency towards male-biased sex ratios in the populations. In recent years, research has defined the relevance of the interactions between the environment and epigenetics playing a key role in the final phenotype. However, the underlying epigenetic mechanisms of individuals exposed to confinement remain elucidated. By using zebrafish (Danio rerio), the DNA methylation promotor region and the gene expression patterns of six genes, namely dnmt1, cyp19a1a, dmrt1, cyp11c1, hsd17b1, and hsd11b2, involved in the DNA maintenance methylation, reproduction, and stress were assessed. Zebrafish larvae were subjected to two high-density conditions (9 and 66 fish/L) during two periods of overlapping sex differentiation of this species (7 to 18 and 18 to 45 days post-fertilization, dpf). Results showed a significant masculinization in the populations of fish subjected to high densities from 18 to 45 dpf. In adulthood, the dnmt1 gene was differentially hypomethylated in ovaries and its expression was significantly downregulated in the testes of fish exposed to high-density. Further, the cyp19a1a gene showed downregulation of gene expression in the ovaries of fish subjected to elevated density, as previously observed in other studies. We proposed dnmt1 as a potential testicular epimarker and the expression of ovarian cyp19a1a as a potential biomarker for predicting stress originated from high densities during the early stages of development. These findings highlight the importance of rearing densities by long-lasting effects in adulthood conveying cautions for stocking protocols in fish hatcheries. [ABSTRACT FROM AUTHOR]

Background: Atrophy of basal forebrain (BF) cholinergic neurons is an early event in Alzheimer's disease (AD) and is associated with cognitive impairment. Down syndrome (DS) is now recognized as a genetically determined form of AD. Therefore, people with DS represent a priority population to study biomarkers of AD pathology and neurodegeneration. Degeneration of BF neurons occurs both in sporadic AD and in DS brains with advanced AD pathology. However, the dynamics of BF atrophy and its changes with age and AT(N) biomarkers have not been studied in DS. Method: We included 246 adults with DS (mean age 43.2 ±11.0 years; 43% female). Volumes of antero‐medial and posterior areas of the BF (amBF and pBF, respectively) were extracted from T1‐weighted 3T MR images using voxel‐based morphometry in SPM12 in combination with a stereotactic atlas of BF functional subdivisions (Figure 1). Differences in amBF and pBF volume in each AD clinical stage (Asymptomatic, Prodromal and Demented) were assessed with Kruskall‐Wallis and pairwise Wilcoxon tests. The relationship of BF volumes with age and AT(N) biomarkers in the cerebrospinal fluid (CSF) (amyloid‐β 42/40 ratio [aβ ratio], phosphorylated Tau 181 [pTau], total Tau [tTau] and neurofilament light [NFL]) was assessed in a subset of subjects (n = 161 [aβ ratio, pTau and tTau] and n = 95 [NFL]) with locally estimated scatterplot smoothing (LOESS) and linear regression in R, respectively. Result: Volumes of amBF and pBF decreased significantly with age (Figure 2), with a steeper decline during the fifth decade of life. BF volumes also declined with AD clinical stage (Figure 3), and had significant correlations with CSF aβ ratio (p<0.001 r2 = 0.22), pTau (p<0.001 r2 = 0.20), tTau (p<0.001 r2 = 0.20) and NFL (p<0.001 r2 = 0.33) (Figure 4). Conclusion: In DS, BF volume decreases with age, AT(N) biomarkers and along the cognitive stages of the AD continuum. [ABSTRACT FROM AUTHOR]

The sex ratio is a key ecological demographic parameter crucial for population viability. However, the epigenetic mechanisms operating during gonadal development regulating gene expression and the sex ratio remain poorly understood. Moreover, there is interest in the development of epigenetic markers associated with a particular phenotype or as sentinels of environmental effects. Here, we profiled DNA methylation and gene expression of 10 key genes related to sex development and stress, including steroidogenic enzymes, and growth and transcription factors. We provide novel information on the sex‐related differences and on the influence of elevated temperature on these genes in zebrafish, a species with mixed genetic and environmental influences on sex ratios. We identified both positive (e.g., amh, cyp11c and hsd11b2) and negative (e.g., cyp11a1 and dmrt1) correlations in unexposed males, and negative correlation (amh) in exposed females between DNA methylation and gene expression levels. Further, we combined DNA methylation analysis with machine learning procedures and found a series of informative CpGs capable not only of correctly identifying sex (based on cyp19a1a DNA methylation levels) but also of identifying whether males and females had been exposed to abnormally elevated temperature when young (based on amh and foxl2a DNA methylation levels, respectively). This was achieved in the absence of conspicuous morphological alterations of the gonads. These DNA methylation‐based epigenetic biomarkers represent molecular resources that can correctly recapitulate past thermal history and pave the way for similar findings in other species to assess potential ecological effects of environmental disturbances in the context of climate change. [ABSTRACT FROM AUTHOR]

Background: Strong associations between age, Alzheimer's disease (AD), and vascular risk factors create challenges to delineate the specific relationships between white matter hyperintensities (WMH) and AD pathophysiology. Down syndrome (DS), a genetically determined form of AD, is not typically complicated by systematic vascular risk factors like hypertension and atherosclerosis and can therefore provide critical information in this regard. We aim to further characterize topography of WMH in DS along the AD continuum and define associations with demographic, genetic, fluid and other imaging biomarkers. Method: In this cross‐sectional study, adults with DS from Down‐Alzheimer Barcelona Neuroimaging Initiative (DABNI) underwent a 3T‐MRI protocol, including 3D‐T1 and 3D‐FLAIR acquisitions. Gray matter (GM) volumes were computed using the CAT12 Toolbox. WMH were segmented using the lesion prediction algorithm implemented in the Lesion Segmentation Toolbox for SPM12. Segmented maps were binarized (threshold of 0.5) and WMH volumes were extracted in each brain lobe, subregions of the corpus callosum, and periventricular versus deep regions (using the standard 10mm limit from the lateral ventricles). Non‐parametric statistical tests were used to assess effects of disease severity on WMH and define associations between WMH and demographic and genetic data, CSF AD biomarkers and GM volumes. Results: We included 116 individuals with DS (Table 1). WMH volume was higher in prodromal and demented groups for all brain regions (Fig 1). Moreover, WMH increased with disease severity such that the demented group demonstrated larger WMH volume than the prodromal group in periventricular regions, frontal and temporal lobes, and body and splenium subregions of the corpus callosum. Total WMH volume was associated with age but not sex, intellectual disability or APOE haplotype (Fig 2). Total WMH volume was negatively related to CSF Aβ42/40 ratio and positively related to CSF t‐tau and p‐tau‐181 concentrations (Fig 3). Associations with GM volumes were widespread, but strongest in parieto‐occipital‐temporal regions. Conclusion: WMH increases with AD pathology and the emergence of clinical symptoms in DS, a population with lower vascular risk factors. It also relates to neurodegeneration in typical AD regions at both asymptomatic and symptomatic stages. Altogether, this suggests that WMH might be intrinsically related to AD pathophysiological processes. [ABSTRACT FROM AUTHOR]

Zebrafish is a worldwide used animal model to better understand cultured fish species; thus, in the last two decades, zebrafish facilities have been created in many aquaculture research centres. However, and despite the attempts of rigorous aseptic conditions for animal husbandry in wet laboratory facilities, the presence of parasites cannot be underestimated. The microsporidium Pseudoloma neurophilia, which mostly affects the central nervous system, has been listed as the most prevalent parasite in reared zebrafish. The emergence of P. neurophilia is usually detected when the individual presents irreversible morphological and/or behavioural symptoms, and consequently, the spread of the disease is inevitable, indicating that the infection is expanded across rearing tanks. This review attempts, for the first time, to collect and discuss the current information on P. neurophilia life cycle, target tissues and symptomatology of the infection occurred in zebrafish. Due to its vertical transmission together with the increasing presence of zebrafish as a model in reproduction‐related problems found in aquaculture, it is highlighted, among others, the sexual dimorphism of the pathogenic effects and the possible transgenerational implications of parasitic infections. Further, to date none effective treatments have been described, so here we provide in detail available diagnostic methods, discussing the importance of the early detection, giving safety‐rearing recommendations to decrease the presence of P. neurophilia. Our intention is to minimize parasite outbreaks in zebrafish facilities, which, on the one hand, can compromise zebrafish welfare, and on the other hand, could interfere furtively in the resulting research previously designed for improving aquaculture production but also other biomedical‐related research. [ABSTRACT FROM AUTHOR]

Abstract Background The response of the trout, O. mykiss, head kidney to bacterial lipopolysaccharide (LPS) or active and attenuated infectious hematopoietic necrosis virus (IHNV and attINHV respectively) intraperitoneal challenge, 24 and 72 hours post-injection, was investigated using a salmonid-specific cDNA microarray. Results The head kidney response to i.p. LPS-induced inflammation in the first instance displays an initial stress reaction involving suppression of major cellular processes, including immune function, followed by a proliferative hematopoietic-type/biogenesis response 3 days after administration. The viral response at the early stage of infection highlights a suppression of hematopoietic and protein biosynthetic function and a stimulation of immune response. In fish infected with IHNV a loss of cellular function including signal transduction, cell cycle and transcriptional activity 72 hours after infection reflects the tissue-specific pathology of IHNV infection. attIHNV treatment on the other hand shows a similar pattern to native IHNV infection at 24 hours however at 72 hours a divergence from the viral response is seen and replace with a recovery response more similar to that observed for LPS is observed. Conclusion In conclusion we have been able to identify and characterise by transcriptomic analysis two different types of responses to two distinct immune agents, a virus, IHNV and a bacterial cell wall component, LPS and a 'mixed' response to an attenuated IHNV. This type of analysis will lead to a greater understanding of the physiological response and the development of effective immune responses in salmonid fish to different pathogenic and pro-inflammatory agents.

AbstractSex plays a crucial role in shaping the immune response of vertebrates, leading to differing susceptibilities to diseases between females and males. This review explores the observed sexually dimorphic patterns in different pathogenic infections, immune responses, and molecular events. First, a compilation of historical guidelines for incorporating gender/sex as a variable in research studies to enhance scientific rigor, improve research outcomes, and promote better health for both sexes has been carried out. Following this, the study focuses on examining sex-based differences in immune responses across different taxa, with an in-depth review of available studies on fish, particularly regarding the prevalence of sex-related differences in parasites, viruses, and bacteria. Furthermore, the benefits of considering sexual dimorphism when evaluating the prevalence of diseases in fish management in aquaculture and ecological contexts have been discussed. Integrating sex in understanding immune responses will positively influence fish welfare, economic impacts, and policymaking, leading to more tailored and effective treatments. [ABSTRACT FROM AUTHOR]

Introduction: Down syndrome (DS) is a genetically determined form of Alzheimer's disease (AD) and a specific form of epilepsy is strongly associated with AD in DS (DSAD), late onset myoclonic epilepsy (LOMEDs), but, there are no clinical trials evaluating the efficacy and tolerability of antiseizure medications in this epilepsy Aims: To describe our experience in the treatment of LOMEDs. Material and Methods: We recruited patients with symptomatic AD (prodromal –pAD‐ or AD dementia –dAD‐ stages) in the context of a health plan for adult population with DS between January 2013 and November 2021. This health plan included semiannual follow‐ups (or as clinically needed) and an anamnesis and structured questionnaire including the personal history of epilepsy (duration of epilepsy, semiology, frequency, efficacy and tolerability of ASM). Results: The study included 72 patients with pAD (48.6% females) and 257 with dAD (50.6% females). Bilateral tonic‐clonic seizures (BTCS) were the most frequent type (85.7% in pAD and 70.7% in dDS) and frequentlly coexisted with myoclonic seizures (16.7% and 57.6% in pDS and dAD respectively). The most frequent treatment after the first seizure was levetiracetam (LEV) (61.5%) followed by valproate (VPA) (19.6%). During follow‐up, 75.8% were on monotherapy with LEV (56.3%), VPA (25.5%) or brivaracetam (BRV) (8.2%). LEV was discontinued due to irritability in 21.9% of patients (interestingly 48% tolerated BRV after LEV discontinuation).VPA was abandoned in 14% due to motor worsening. Seizure control at one year was achieved in 65.9%, when considering BTCS, but only 30.2% were free of of myoclonic seizures. Discussion: LOMEDs is a very common comorbidity in DSAD that responds partially to treatment. BTCS seem to have a better response to treatment compared to myoclonic seizures. [ABSTRACT FROM AUTHOR]

Epigenetics integrates genomic and environmental information to produce a given phenotype. Here, the model of Conserved Epigenetic Regulation of Sex (CERS) is discussed. This model is based on our knowledge on genes involved in sexual development and on epigenetic regulation of gene expression activation and silencing. This model was recently postulated to be applied to the sexual development of fish, and it states that epigenetic and gene expression patterns are more associated with the development of a particular gonadal phenotype, e.g., testis differentiation, rather than with the intrinsic or extrinsic causes that lead to the development of this phenotype. This requires the existence of genes with different epigenetic modifications, for example, changes in DNA methylation levels associated with the development of a particular sex. Focusing on DNA methylation, the identification of CpGs, the methylation of which is linked to sex, constitutes the basis for the identification of Essential Epigenetic Marks (EEM). EEMs are defined as the number and identity of informative epigenetic marks that are strictly necessary, albeit perhaps not sufficient, to bring about a specific, measurable, phenotype of interest. Here, we provide a summary of the genes where DNA methylation has been investigated so far, focusing on fish. We found that cyp19a1a and dmrt1 , two key genes for ovary and testis development, respectively, consistently show an inverse relationship between their DNA methylation and expression levels, thus following CERS predictions. However, in foxl2a , a pro-female gene, and amh , a pro-male gene, such relationship is not clear. The available data of other genes related to sexual development such as sox9 , gsdf , and amhr2 are also discussed. Next, we discuss the use of CERS to make testable predictions of how sex is epigenetically regulated and to better understand sexual development, as well as the use of EEMs as tools for the diagnosis and prognosis of sex. We argue that CERS can aid in focusing research on the epigenetic regulation of sexual development not only in fish but also in vertebrates in general, particularly in reptiles with temperature sex-determination, and can be the basis for possible practical applications including sex control in aquaculture and also in conservation biology. [ABSTRACT FROM AUTHOR]

Sex is remarkably plastic in fish and can be easily influenced by environmental cues, in which temperature has been the most studied abiotic factor. However, it has been shown that elevated population densities can increase the number of males in several species but little is known about the underlying molecular mechanisms and whether general patterns exist. Here, we studied the long‐term effects of population density on the gene expression program in zebrafish gonads. The ovarian transcriptome of females exposed to high versus low population densities contained 4,634 differentially expressed genes. Among them, a set of promale genes (amh, sypc3, spata6, and sox3) were upregulated in the high‐population density group. Next, we compared the transcriptomes of ovaries of female zebrafish resistant to the masculinizing effects of either high density or elevated temperature. Results showed a set of 131 and 242 common upregulated and downregulated genes, respectively, including the upregulation of known male‐related genes (e.g., amh and sycp3) but also genes involved in other functions (e.g., faima, ccm21, and ankrd6b) and a downregulation of cyp19a1a together with other genes (e.g., lgals9l1 and ubxn2a). We identified the common Gene Ontology terms involved in the reproduction and sexual development that were consistently affected in both environmental factors. These results show that regardless of the environmental perturbation there are common genes and cellular functions involved in the resistance to masculinization. These altered gene‐expression profiles can be used as markers indicative of previous exposure to environmental stress independent of conspicuous alterations in sex ratios or gonadal morphology. HIGHLIGHTS: We identify, in otherwise apparently normal fish ovaries, a series of common persistent gene expression changes that can be used as markers indicative of previous exposure to environmental perturbations of both biotic and abiotic origin. [ABSTRACT FROM AUTHOR]

Background: Down's syndrome (DS) is a genetic form of Alzheimer´s disease (AD). Plasma NfL is a neurodegeneration biomarker which has shown excellent diagnostic and prognostic performances. However, its association with brain atrophy has not been established. Methods: Single‐centre cross‐sectional study in adults with DS. Participants had blood drawn and underwent an MRI and were classified into asymptomatic and symptomatic AD patients after a structured neurological and neuropsychological evaluation blind to the biomarker data. Plasma Neurofilament light (NfL) levels were determined with SIMOA and cortical thickness (CTh) with Freesurfer. We assessed the correlation of plasma NfL levels with CTh across the cortical mantel and with the Dickerson´s CTh signature. Results: We recruited 169 adults with DS (74 females, mean age 42.85 [18.23 – 61.79] years old), of which 114 were asymptomatic (46 females, mean age 38.44 [18.23 – 57.17] years old) and 55 symptomatic (mean age 51.99 [39.40 – 61.79] years old). Plasma NfL levels were associated with cortical atrophy only in the symptomatic AD group in widespread medial and lateral posterior cortical regions (Figure 1). Plasma NfL showed a moderate negative correlation (r= ‐0.54; p<0.01) with Dickerson´s cortical signature (Figure 2). Conclusions: Plasma NfL levels are a good biomarker to track neurodegeneration in DS associated AD. [ABSTRACT FROM AUTHOR]

Background: The role of epigenetic modifications such as DNA methylation during vertebrate sexual development is far from being clear. Using the zebrafish model, we tested the effects of one of the most common DNA methyltransferase (dnmt) inhibitor, 5-aza-2'-deoxycytidine (5-aza-dC), which is approved for the treatment of acute myeloid leukaemia and is under active investigation for the treatment of solid tumours. Several dose-response experiments were carried out during two periods, including not only the very first days of development (0-6 days post-fertilization, dpf), as done in previous studies, but also, and as a novelty, the period of gonadal development (10-30 dpf). Results: Early treatment with 5-aza-dC altered embryonic development, delayed hatching and increased teratology and mortality, as expected. The most striking result, however, was an increase in the number of females, suggesting that alterations induced by 5-aza-dC treatment can affect sexual development as well. Results were confirmed when treatment coincided with gonadal development. In addition, we also found that the adult gonadal transcriptome of 5-aza-dC-exposed females included significant changes in the expression of key reproduction-related genes (e.g. cyp11a1, esr2b and figla), and that several pro-female-related pathways such as the Fanconi anaemia or the Wnt signalling pathways were downregulated. Furthermore, an overall inhibition of genes implicated in epigenetic regulatory mechanisms (e.g. dnmt1, dicer, cbx4) was also observed. Conclusions: Taken together, our results indicate that treatment with a DNA methylation inhibitor can also alter the sexual development in zebrafish, with permanent alterations of the adult gonadal transcriptome, at least in females. Our results show the importance of DNA methylation for proper control of sexual development, open new avenues for the potential control of sex ratios in fish (aquaculture, population control) and call attention to possibly hidden long-term effects of dnmt therapy when used, for example, in the treatment of prepuberal children affected by some types of cancer. [ABSTRACT FROM AUTHOR]

The zebrafish (Danio rerio) has become a well-established experimental model in many research fields but the loss of the primary sex-determining region during the process of domestication renders laboratory strains of zebrafish susceptible to the effects of environmental factors on sex ratios. Further, an essential husbandry aspect - the optimal rearing density to avoid stress-induced masculinization - is not known. We carried out two experiments: the first focusing on the effects of density on survival, growth and sex ratio by rearing zebrafish at different initial densities (9, 19, 37 and 74 fish per litre) for 3 months (6-90 days post-fertilization, dpf), and the second focusing on the effects of cortisol during the sex differentiation period (15-45 dpf) for zebrafish reared at low density. The results showed an increase in the number of males in groups subjected to the two highest initial rearing densities; we also observed a reduction of survival and growth in a density-dependent manner. Furthermore, zebrafish treated with cortisol during the sex differentiation period showed a complete masculinization of the population; treatment with the cortisol synthesis inhibitor metyrapone negated the effects of exogenous cortisol. Our results indicate that the process of sex differentiation in domesticated zebrafish can be perturbed by elevated stocking density and that this effect is likely to be mediated by an increase in cortisol through the stress response. However, the underlying mechanism needs further study. [ABSTRACT FROM AUTHOR]

Background: Controlling sex ratios is essential for the aquaculture industry, especially in those species with sex dimorphism for relevant productive traits, hence the importance of knowing how the sexual phenotype is established in fish. Turbot, a very important fish for the aquaculture industry in Europe, shows one of the largest sexual growth dimorphisms amongst marine cultured species, being all-female stocks a desirable goal for the industry. Although important knowledge has been achieved on the genetic basis of sex determination (SD) in this species, the master SD gene remains unknown and precise information on gene expression at the critical stage of sex differentiation is lacking. In the present work, we examined the expression profiles of 29 relevant genes related to sex differentiation, from 60 up to 135 days post fertilization (dpf), when gonads are differentiating. We also considered the influence of three temperature regimes on sex differentiation. Results: The first sex-related differences in molecular markers could be observed at 90 days post fertilization (dpf) and so we have called that time the onset of sex differentiation. Three genes were the first to show differential expression between males and females and also allowed us to sex turbot accurately at the onset of sex differentiation (90 dpf): cyp19a1a, amh and vasa. The expression of genes related to primordial germ cells (vasa, gsdf, tdrd1) started to increase between 75-90 dpf and vasa and tdrd1 later presented higher expression in females (90-105 dpf). Two genes placed on the SD region of turbot (sox2, fxr1) did not show any expression pattern suggestive of a sex determining function. We also detected changes in the expression levels of several genes (ctnnb1, cyp11a, dmrt2 or sox6) depending on culture temperature. Conclusion: Our results enabled us to identify the first sex-associated genetic cues (cyp19a1a, vasa and amh) at the initial stages of gonad development in turbot (90 dpf) and to accurately sex turbot at this age, establishing the correspondence between gene expression profiles and histological sex. Furthermore, we profiled several genes involved in sex differentiation and found specific temperature effects on their expression. [ABSTRACT FROM AUTHOR]

The zebrafish ( Danio rerio) is a freshwater teleost of the family Cyprinidae that is established as a model organism in many research fields. Here, we define the characteristics that a fish species should have to serve as a model for finfish aquaculture research and argue that the zebrafish fulfils essentially most of them. We first describe several aspects of the biology of the zebrafish including phylogenetic relationships, development and growth and reproduction, both in the wild and under laboratory conditions. Next, we review the work already carried out in zebrafish that is related to different aspects of aquaculture research (reproduction, stress, pathology, toxicology nutrition and growth). We assess critically the areas in which zebrafish still offers further potential as a model organism for aquaculture, which include, but are not limited to, development, immunology, genomics and reproduction. In other areas, however, limitations must be borne in mind and caution must be taken when extrapolating results. This is, for example, the case of some growth studies. Finally, we provide information on resources for research with zebrafish. Current general limitations of work with zebrafish come from the fact that in contrast to other laboratory animal models such as rodents, strict breeding protocols are generally not adopted. Nevertheless, as there is no major obstacle to overcome these limitations and due to its intrinsic advantages, we conclude that the zebrafish is likely to play an increasing role as a model organism in many areas of research for finfish aquaculture. [ABSTRACT FROM AUTHOR]

The article discusses a study on zebrafish Danio rerio, and evaluating the influence of stocking density on fish sex and it induces masculinization. Topics include impact of evaluating breeding pair with female-biased sex ratios; effect of stocking density on sex ratio; and influence of density on sex in some genetically distinct families.

Background: Food supply is a major factor influencing growth rates in animals. This has important implications for both natural and farmed fish populations, since food restriction may difficult reproduction. However, a study on the effects of food supply on the development of juvenile gonads has never been transcriptionally described in fish. Methods and Findings: This study investigated the consequences of growth on gonadal transcriptome of European sea bass in: 1) 4-month-old sexually undifferentiated fish, comparing the gonads of fish with the highest vs. the lowest growth, to explore a possible link between transcriptome and future sex, and 2) testis from 11-month-old juveniles where growth had been manipulated through changes in food supply. The four groups used were: i) sustained fast growth, ii) sustained slow growth, iii) accelerated growth, iv) decelerated growth. The transcriptome of undifferentiated gonads was not drastically affected by initial natural differences in growth. Further, changes in the expression of genes associated with protein turnover were seen, favoring catabolism in slow-growing fish and anabolism in fast-growing fish. Moreover, while fast-growing fish took energy from glucose, as deduced from the pathways affected and the analysis of protein-protein interactions examined, in slow-growing fish lipid metabolism and gluconeogenesis was favored. Interestingly, the highest transcriptomic differences were found when forcing initially fast-growing fish to decelerate their growth, while accelerating growth of initially slow-growing fish resulted in full transcriptomic convergence with sustained fast-growing fish. Conclusions: Food availability during sex differentiation shapes the juvenile testis transcriptome, as evidenced by adaptations to different energy balances. Remarkably, this occurs in absence of major histological changes in the testis. Thus, fish are able to recover transcriptionally their testes if they are provided with enough food supply during sex differentiation; however, an initial fast growth does not represent any advantage in terms of transcriptional fitness if later food becomes scarce. [ABSTRACT FROM AUTHOR]

Controlling the sex ratio is essential in finfish farming. A balanced sex ratio is usually good for broodstock management, since it enables to develop appropriate breeding schemes. However, in some species the production of monosex populations is desirable because the existence of sexual dimorphism, primarily in growth or first time of sexual maturation, but also in color or shape, can render one sex more valuable.The knowledge of the genetic architecture of sex determination (SD) is convenient for controlling sex ratio and for the implementation of breeding programs. Unlike mammals and birds, which show highly conserved master genes that control a conserved genetic network responsible for gonad differentiation (GD), a huge diversity of SD mechanisms has been reported in fish. Despite theory predictions, more than one gene is in many cases involved in fish SD and genetic differences have been observed in the GD network. Environmental factors also play a relevant role and epigenetic mechanisms are becoming increasingly recognized for the establishment and maintenance of the GD pathways. Although major genetic factors are frequently involved in fish SD, these observations strongly suggest that SD in this group resembles a complex trait. Accordingly, the application of quantitative genetics combined with genomic tools is desirable to address its study and in fact, when applied, it has frequently demonstrated a multigene trait interacting with environmental factors in model and cultured fish species. This scenario has notable implications for aquaculture and, depending upon the species, from chromosome manipulation or environmental control techniques up to classical selection or marker assisted selection programs, are being applied. In this review, we selected four relevant species or fish groups to illustrate this diversity and hence the technologies that can be used by the industry for the control of sex ratio: turbot and European sea bass, two reference species of the European aquaculture, and salmonids and tilapia, representing the fish for which there are well established breeding programs. [ABSTRACT FROM AUTHOR]

Abstract: The phenotype results from the interaction between the genotype and the environment but how a given environment drives the expression of a particular sexual phenotype is poorly understood. The European sea bass has a polygenic sex determining mechanism influenced by temperature and, as in any poikilotherm, temperature also affects growth rates. However, the exact relationship between growth and sex differentiation remains elusive. To analyze this relationship, two experiments involving the manipulation of fish growth with or without a previous size-grading were carried out. In the first experiment, sex ratios of non-size-graded fish were unaltered after disturbing growth rates at three different times during the sex differentiation period corresponding to fish of 8–12cm standard length (SL). The groups with a reduction of their food intake (hence showing slow growth rates) exhibited catch-up growth after returning to normal feeding levels and also exhibited a degree of gonadal differentiation and maturation similar to that of the controls. In the second experiment, fish of ~4cm SL, i.e., before the appearance of the first known differences in aromatase expression (5–6cm SL), were size-graded and then subdivided into groups which were differentially fed to maximize differences in their resulting growth rates. Highly significant differences in sex ratios were found, with more females in the groups derived from the group with the largest fish at the time of grading irrespective of subsequent growth rates. Together, these results show that in the European sea bass sex-related differences in growth are established before the appearance of the currently known first molecular markers of sex and that growth rates during the sex differentiation period do not affect sex ratios. Based on these results, we propose the 3–4cm as the size range where possible earlier differences between sexes should be looked for at the molecular level in the European sea bass. Moreover, from an applied point of view, we suggest that improvement of aquaculture protocols for this species might be achieved by combining size-grading to discard slow growing fish, and hence males, together with the control of the catch-up growth response in an attempt to reduce the amount of required food. [Copyright &y& Elsevier]

Background: Genomic resources for plant and animal species that are under exploitation primarily for human consumption are increasingly important, among other things, for understanding physiological processes and for establishing adequate genetic selection programs. Current available techniques for high-throughput sequencing have been implemented in a number of species, including fish, to obtain a proper description of the transcriptome. The objective of this study was to generate a comprehensive transcriptomic database in turbot, a highly priced farmed fish species in Europe, with potential expansion to other areas of the world, for which there are unsolved production bottlenecks, to understand better reproductive- and immune-related functions. This information is essential to implement marker assisted selection programs useful for the turbot industry. Results: Expressed sequence tags were generated by Sanger sequencing of cDNA libraries from different immunerelated tissues after several parasitic challenges. The resulting database ("Turbot 2 database") was enlarged with sequences generated from a 454 sequencing run of brain-hypophysis-gonadal axis-derived RNA obtained from turbot at different development stages. The assembly of Sanger and 454 sequences generated 52,427 consensus sequences ("Turbot 3 database"), of which 23,661 were successfully annotated. A total of 1,410 sequences were confirmed to be related to reproduction and key genes involved in sex differentiation and maturation were identified for the first time in turbot (AR, AMH, SRY-related genes, CYP19A, ZPGs, STAR FSHR, etc.). Similarly, 2,241 sequences were related to the immune system and several novel key immune genes were identified (BCL, TRAF, NCK, CD28 and TOLLIP, among others). The number of genes of many relevant reproduction- and immune-related pathways present in the database was 50-90% of the total gene count of each pathway. In addition, 1,237 microsatellites and 7,362 single nucleotide polymorphisms (SNPs) were also compiled. Further, 2,976 putative natural antisense transcripts (NATs) including microRNAs were also identified. Conclusions: The combined sequencing strategies employed here significantly increased the turbot genomic resources available, including 34,400 novel sequences. The generated database contains a larger number of genes relevant for reproduction- and immune-associated studies, with an excellent coverage of most genes present in many relevant physiological pathways. This database also allowed the identification of many microsatellites and SNP markers that will be very useful for population and genome screening and a valuable aid in marker assisted selection programs. [ABSTRACT FROM AUTHOR]

In the wild, water temperature cycles daily: it warms up after sunrise, and cools rapidly after sunset. Surprisingly, the impact of s°Ch daily thermocycles during the early development of fish remains neglected. We investigated the influence of constant vs daily thermocycles in zebrafish, from embryo development to sexual differentiation, by applying four temperature regimens: two constant (24°C and 28°C) and two daily thermocycles: 28:24°C, TC (thermophase coinciding with daytime, and cryophase coinciding with night-time) and 24:28°C, CT (opposite to TC) in a 12:12 h light:dark cycle (LD). Embryo development was temperature-dependent but enhanced at 28°C and TC. Hatching rhythms were diurnal (around 4 h after lights on), but temperature- and cycle-sensitive, since hatching occurred sooner at 28°C (48 hours post fertilization; hpf) while it was delayed at 24°C (96 hpf). Under TC, hatching occurred at 72 hpf, while under CT hatching displayed two peaks (at 70 hpf and 94 hpf). In constant light (LL) or darkness (DD), hatching rhythms persisted with tau close to 24 h, suggesting a clock-controlled ''gating'' mechanism. Under 28°C or TC, larvae showed the best performance (high growth and survival, and low malformations). The sex ratio was strongly influenced by temperature, as the proportion of females was higher in CT and TC (79 and 83% respectively), contrasting with 28°C and 24°C, which led to more males (83 and 76%). Ovarian aromatase (cyp19a) expression in females was highest in TC and CT (6.5 and 4.6 fold higher than at 28°C, respectively); while anti-mü llerian hormone (amh) expression in males increased in testis at 24°C (3.6 fold higher compared to TC) and particularly at 28°C (14.3 fold increase). Taken together, these findings highlight the key role of environmental cycles during early development, which shaped the daily rhythms in fish embryo and larvae, and ultimately influenced sex differentiation. [ABSTRACT FROM AUTHOR]

Sex ratio shifts in response to temperature are common in fish and reptiles. However, the mechanism linking temperature during early development and sex ratios has remained elusive. We show in the European sea bass (sb), a fish in which temperature effects on sex ratios are maximal before the gonads form, that juvenile males have double the DNA methylation levels of females in the promoter of gonadal aromatase (cyp19a), the enzyme that converts androgens into estrogens. Exposure to high temperature increased the cyp19a promoter methylation levels of females, indicating that induced-masculinization involves DNA methylation-mediated control of aromatase gene expression, with an observed inverse relationship between methylation levels and expression. Although different CpGs within the sb cyp19a promoter exhibited different sensitivity to temperature, we show that the increased methylation of the sb cyp19a promoter, which occurs in the gonads but not in the brain, is not a generalized effect of temperature. Importantly, these effects were also observed in sexually undifferentiated fish and were not altered by estrogen treatment. Thus, methylation of the sb cyp19a promoter is the cause of the lower expression of cyp19a in temperature-masculinized fish. In vitro, induced methylation of the sb cyp19a promoter suppressed the ability of SF-1 and Foxl2 to stimulate transcription. Finally, a CpG differentially methylated by temperature and adjacent to a Sox transcription factor binding site is conserved across species. Thus, DNA methylation of the aromatase promoter may be an essential component of the long-sought-after mechanism connecting environmental temperature and sex ratios in vertebrate species with temperature-dependent sex determination. [ABSTRACT FROM AUTHOR]

Background: Throughout the primary literature and within textbooks, the erythrocyte has been tacitly accepted to have maintained a unique physiological role; namely gas transport and exchange. In non-mammalian vertebrates, nucleated erythrocytes are present in circulation throughout the life cycle and a fragmented series of observations in mammals support a potential role in non-respiratory biological processes. We hypothesised that nucleated erythrocytes could actively participate via ligand-induced transcriptional re-programming in the immune response. Methodology/Principal Findings: Nucleated erythrocytes from both fish and birds express and regulate specific pattern recognition receptor (PRR) mRNAs and, thus, are capable of specific pathogen associated molecular pattern (PAMP) detection that is central to the innate immune response. In vitro challenge with diverse PAMPs led to de novo specific mRNA synthesis of both receptors and response factors including interferon-alpha (IFNα) that exhibit a stimulus-specific polysomal shift supporting active translation. RNA-Seq analysis of the PAMP (Poly (I:C), polyinosinic:polycytidylic acid)-erythrocyte response uncovered diverse cohorts of differentially expressed mRNA transcripts related to multiple physiological systems including the endocrine, reproductive and immune. Moreover, erythrocyte-derived conditioned mediums induced a type-1 interferon response in macrophages thus supporting an integrative role for the erythrocytes in the immune response. Conclusions/Significance: We demonstrate that nucleated erythrocytes in non-mammalian vertebrates spanning significant phylogenetic distance participate in the immune response. RNA-Seq studies highlight a mRNA repertoire that suggests a previously unrecognized integrative role for the erythrocytes in other physiological systems. [ABSTRACT FROM AUTHOR]

Amphibians are experiencing a panzootic of unprecedented proportions caused by the emergence of Batrachochytrium dendrobatidis (Bd). However, all species are not equally at risk of infection, and risk is further modified by environmental variables, specifically temperature. In order to understand how, and when, hosts mount a response to Bd we analysed infection dynamics and patterns of gene expression in the model amphibian species Silurana (Xenopus) tropicalis. Mathematical modelling of infection dynamics demonstrate the existence of a temperature-dependent protective response that is largely independent of the intrinsic growth-rate of Bd. Using temporal expression-profiling by microarrays and qRTPCR, we characterise this response in the main amphibian lymphoid tissue, the spleen. We demonstrate that clearance of Bd at the host-optimal temperature is not clearly associated with an adaptive immune response, but rather is correlated with the induction of components of host innate immunity including the expression of genes that are associated with the production of the antimicrobial skin peptide preprocareulein (PPCP) as well as inflammatory responses. We find that adaptive immunity appears to be lacking at host-optimal temperatures. This suggests that either Bd does not stimulate, or suppresses, adaptive immunity, or that trade-offs exist between innate and adaptive limbs of the amphibian immune system. At cold temperatures, S. tropicalis loses the ability to mount a PPCP-based innate response, and instead manifests a more pronounced inflammatory reaction that is characterised by the production of proteases and higher pathogen burdens. This study demonstrates the temperature-dependency of the amphibian response to infection by Bd and indicates the influence that changing climates may exert on the ectothermic host response to pathogens. [ABSTRACT FROM AUTHOR]

Background: Individuals of many vertebrate species show different stress coping styles and these have a striking influence on how gene expression shifts in response to a variety of challenges. Principal Findings: This is clearly illustrated by a study in which common carp displaying behavioural predictors of different coping styles (characterised by a proactive, adrenaline-based or a reactive, cortisol-based response) were subjected to inflammatory challenge and specific gene transcripts measured in individual brains. Proactive and reactive fish differed in baseline gene expression and also showed diametrically opposite responses to the challenge for 80% of the genes investigated. Significance: Incorporating coping style as an explanatory variable can account for some the unexplained variation that is common in gene expression studies, can uncover important effects that would otherwise have passed unnoticed and greatly enhances the interpretive value of gene expression data. [ABSTRACT FROM AUTHOR]

Background: The response of the trout, O. mykiss, head kidney to bacterial lipopolysaccharide (LPS) or active and attenuated infectious hematopoietic necrosis virus (IHNV and attINHV respectively) intraperitoneal challenge, 24 and 72 hours post-injection, was investigated using a salmonid-specific cDNA microarray. Results: The head kidney response to i.p. LPS-induced inflammation in the first instance displays an initial stress reaction involving suppression of major cellular processes, including immune function, followed by a proliferative hematopoietic-type/biogenesis response 3 days after administration. The viral response at the early stage of infection highlights a suppression of hematopoietic and protein biosynthetic function and a stimulation of immune response. In fish infected with IHNV a loss of cellular function including signal transduction, cell cycle and transcriptional activity 72 hours after infection reflects the tissue-specific pathology of IHNV infection. attIHNV treatment on the other hand shows a similar pattern to native IHNV infection at 24 hours however at 72 hours a divergence from the viral response is seen and replace with a recovery response more similar to that observed for LPS is observed. Conclusion: In conclusion we have been able to identify and characterise by transcriptomic analysis two different types of responses to two distinct immune agents, a virus, IHNV and a bacterial cell wall component, LPS and a 'mixed' response to an attenuated IHNV. This type of analysis will lead to a greater understanding of the physiological response and the development of effective immune responses in salmonid fish to different pathogenic and pro-inflammatory agents. [ABSTRACT FROM AUTHOR]

Understanding how gilthead sea bream,Sparus aurataL., an important Mediterranean Sea species for aquaculture, respond physiologically to stressors commonly encountered in intensive rearing is important for effective production, as managing for stress is a major factor in maintaining healthy fish stocks. Our objective was to determine whether holding juvenile gilthead sea bream at a high density (HD), as a chronic stressor, would affect their physiological responses to a subsequent acute handling stressor. After acclimation at a low density (LD) of 6 kg m−3 in 200-L circular tanks containing 33–36 g L−1 recirculating seawater at 19°C under a normal photoperiod, juvenile 37-g gilthead sea bream were confined for 14 days at a HD of 26 kg m−3 and then subjected to 30-s aerial emersion in a dipnet. Plasma levels of cortisol, glucose, lactate, osmolality and chloride were determined in fish held in separate lots during LD (control) and HD confinement at 0, 1, 2, 7 and 14 days, and then after handling at 0, 1, 2, 4 and 8 h. Although plasma cortisol levels were similar in LD and HD fish groups after 14 d of confinement (15 and 23 ng mL−1, respectively), the cortisol response in fish from the HD treatment at 1 and 2 h following acute handling (70 and 37 ng mL−1, respectively) was only about half of that measured in the control group (139 and 102 ng mL−1); plasma cortisol was similar in both groups by 4 and 8 h. In contrast, plasma glucose elevations in response to handling were higher at 4 and 8 h in the HD-held fish (94 and 72 mg dL−1, respectively) than in those from the LD treatment (59 and 51 mg dL−1); glucose responses were similar in both groups at 1 and 2 h after handling and throughout confinement. Plasma lactate levels were higher in LD fish than in the HD group at the beginning of the experiment but were similar after 14 d confinement and responses to handling were similar (e.g. 33 and 35 mg dL−1 at 1 h). Plasma osmolality showed increases during the first 2 h after acute handling but no differences were evident between the two density treatments at any time during confinement or posthandling. Plasma chloride levels did not change throughout the experiment. The reduced plasma cortisol response to acute handling likely resulted from negative feedback of mildly but chronically elevated circulating cortisol caused by the confinement stressor on the hypothalamic–pituitary–interrenal axis. While other post-handling physiological changes also showed differences between treatment groups, the suppressed cortisol response in the HD-held fish suggests a reduction in the gilthead sea bream's normal capacity to respond to an acute stressor. [ABSTRACT FROM AUTHOR]

Accumulating evidence shows that environmental changes can affect population sex ratios through epigenetic regulation of gene expression in species where sex depends on both genetic and environmental cues. Sometimes, altered sex ratios persist in the next generation even when the environmental cue is no longer present (a multigenerational effect). However, evidence of transgenerational effects (i.e., beyond the first non-exposed generation), which tend to be paternally transmitted, is scarce and a matter of debate. Here, we used the AB strain of zebrafish, where sex depends on both genetic and environmental influences, to study possible multi- (to the F 1) and transgenerational (to the F 2) effects of elevated temperature during the critical period of sex differentiation. From eight initial different families, five were selected in order to capture sufficient variation between the sex ratio of the control group (28 °C) and the group exposed to elevated (35 °C) temperature only at the parental (P) generation. Results showed a consistent increase in the proportion of males in the P generation in all five families as a result of heat treatment. Sex ratios were then determined in the F 1 and F 2 offspring derived from both above groups, which were all raised at 28 °C. A persisting male-skewed sex ratio in the 35°C-derived, unexposed offspring of the F 1 generation was observed in three families, denoting family-dependent multigenerational effects. However, no transgenerational effects were observed in the F 2 generation of any family. DNA methylation was also assessed in the testis of P, F 1 and F 2 males derived from exposed and non-exposed fathers and grandfathers. DNA methylation was significantly decreased only in the testis of the 35°C-derived males in the F 1 generation but not of the F 2 generation and, surprisingly, neither in the 35°C-exposed males of the P generation. Taken together, our results show great interfamily variation, not only in sex ratio response to elevated temperature, but also on its multigenerational effects, denoting a strong influence of genetics. Alterations in the testicular epigenome in F 1 males calls for attention to possible, previously unnoticed, effects of temperature in the unexposed offspring of heat-exposed parents in a global warming scenario. • Temperature effects on sex ratio in the unexposed F 1 are family-dependent. • Temperature effects on sex ratio in the unexposed F 2 were not observed. • Testicular epigenome hypomethylation was observed in the F 1 but not in the F 2. • Thus, temperature can affect the unexposed offspring of heat-exposed parents. • Epigenetic inheritance can play a crucial role in a global warming scenario. [ABSTRACT FROM AUTHOR]

Sex ratio depends on sex determination mechanisms and is a key demographic parameter determining population viability and resilience to natural and anthropogenic stressors. There is increasing evidence that the environment can alter sex ratio even in genetically sex-determined species (GSD), as elevated temperature can cause female-to-male sex reversal (neomales). Alarmingly, neomales are being discovered in natural populations of several fish, amphibian and reptile species worldwide. Understanding the basis of neomale development is important for conservation biology. Among GSD species, it is unknown whether those with chromosomal sex determination (CSD), the most common system, will better resist the influence of high temperature than those with polygenic sex determination (PSD). Here, we compared the effects of elevated temperature in two wild zebrafish strains, Nadia (NA) and Ekkwill (EKW), which have CSD with a ZZ/ZW system, against the AB laboratory strain, which has PSD. First, we uncovered novel sex genotypes and the results showed that, at control temperature, the masculinization rate roughly doubled with the addition of each Z chromosome, while some ZW and WW fish of the wild strains became neomales. Surprisingly, we found that at elevated temperatures WW fish were just as likely as ZW fish to become neomales and that all strains were equally susceptible to masculinization. These results demonstrate that the Z chromosome is not essential for male development and that the dose of W buffers masculinization at the control temperature but not at elevated temperature. Furthermore, at the elevated temperature the testes of neomales, but not of normal males, contained more spermatozoa than at the control temperature. Our results show in an unprecedented way that, in a global warming scenario, CSD species may not necessarily be better protected against the masculinizing effect of elevated temperature than PSD species, and reveal genotype-by-temperature interactions in male sex determination and spermatogenesis. [ABSTRACT FROM AUTHOR]