Modeling human neurodevelopmental diseases with brain organoids

Studying the etiology of human neurodevelopmental diseases has long been a challenging task due to the brain’s complexity and its limited accessibility. Human pluripotent stem cells (hPSCs)-derived brain organoids are capable of recapitulating various features and functionalities of the human brain, allowing the investigation of intricate pathogenesis of developmental abnormalities. Over the past years, brain organoids have facilitated identifying disease-associated phenotypes and underlying mechanisms for human neurodevelopmental diseases. Integrating with more cutting-edge technologies, particularly gene editing, brain organoids further empower human disease modeling. Here, we review the latest progress in modeling human neurodevelopmental disorders with brain organoids.

Model systems in SDHx-related pheochromocytoma/paraganglioma

Pheochromocytoma (PHEO) and paraganglioma (PGL) (together PPGL) are tumors with poor outcomes that arise from neuroendocrine cells in the adrenal gland, and sympathetic and parasympathetic ganglia outside the adrenal gland, respectively. Many follow germline mutations in genes coding for subunits of succinate dehydrogenase (SDH), a tetrameric enzyme in the tricarboxylic acid (TCA) cycle that both converts succinate to fumarate and participates in electron transport. Germline SDH subunit B (SDHB) mutations have a high metastatic potential. Herein, we review the spectrum of model organisms that have contributed hugely to our understanding of SDH dysfunction. In Saccharomyces cerevisiae (yeast), succinate accumulation inhibits alpha-ketoglutarate-dependent dioxygenase enzymes leading to DNA demethylation. In the worm Caenorhabditis elegans, mutated SDH creates developmental abnormalities, metabolic rewiring, an energy deficit and oxygen hypersensitivity (the latter is also found in Drosophila melanogaster). In the zebrafish Danio rerio, sdhb mutants display a shorter lifespan with defective energy metabolism. Recently, SDHB-deficient pheochromocytoma has been cultivated in xenografts and has generated cell lines, which can be traced back to a heterozygous SDHB-deficient rat. We propose that a combination of such models can be efficiently and effectively used in both pathophysiological studies and drug-screening projects in order to find novel strategies in PPGL treatment.

Reproductive toxicological changes in avian embryos due to a pesticide and an environmental contaminant

Single and simultaneous toxic effects of glyphosate (Amega Up, 360 g L−1, 4%) and copper sulphate (0.01%) were studied in avian embryos treated either with injection directly into the air chamber or by immersion application for 30 min on day 0 of incubation. Alterations of the chicken embryos were evaluated during necropsy performed on day 19 of incubation, together with mortality, body weight and the type of developmental abnormalities. Based on the results, the injection application appeared to be more toxic than the immersion method, as it induced increased mortality and reduced the average body weight, and resulted in a higher incidence of congenital anomalies. Supposedly, a toxicodynamic interaction occurs between copper sulphate and glyphosate, which may reduce the vitality of embryos and thus decrease the number of offspring in wild birds.

Sex- and tissue-specific effects of binge levels of prenatal alcohol consumption on DNA methylation at birth

Background: Binge level prenatal alcohol exposure (PAE) causes developmental abnormalities, which may be mediated in part by epigenetic mechanisms. Despite this, few studies have characterised the association of binge PAE with DNA methylation in offspring. Methods: We investigated the association between binge PAE and genome-wide DNA methylation profiles in a sex-specific manner in neonatal buccal and placental samples. Results: We identified no differentially methylated CpGs or differentially methylated regions (DMRs) at false discovery rate <0.05. However, using a sum-of-ranks approach, we identified a DMR in each tissue of female offspring. The DMR identified in buccal samples is located near regions with previously-reported associations to fetal alcohol spectrum disorder (FASD) and binge PAE. Conclusion: Our findings warrant further replication and highlight a potential epigenetic link between binge PAE and FASD.

Molecular Mechanisms of the RECQ4 Pathogenic Mutations

The human RECQ4 gene encodes an ATP-dependent DNA helicase that contains a conserved superfamily II helicase domain located at the center of the polypeptide. RECQ4 is one of the five RECQ homologs in human cells, and its helicase domain is flanked by the unique amino and carboxyl termini with sequences distinct from other members of the RECQ helicases. Since the identification of the RECQ4 gene in 1998, multiple RECQ4 mutations have been linked to the pathogenesis of three clinical diseases, which are Rothmund-Thomson syndrome, Baller-Gerold syndrome, and RAPADILINO. Patients with these diseases show various developmental abnormalities. In addition, a subset of RECQ4 mutations are associated with high cancer risks, especially for osteosarcoma and/or lymphoma at early ages. The discovery of clinically relevant RECQ4 mutations leads to intriguing questions: how is the RECQ4 helicase responsible for preventing multiple clinical syndromes? What are the mechanisms by which the RECQ4 disease mutations cause tissue abnormalities and drive cancer formation? Furthermore, RECQ4 is highly overexpressed in many cancer types, raising the question whether RECQ4 acts not only as a tumor suppressor but also an oncogene that can be a potential new therapeutic target. Defining the molecular dysfunctions of different RECQ4 disease mutations is imperative to improving our understanding of the complexity of RECQ4 clinical phenotypes and the dynamic roles of RECQ4 in cancer development and prevention. We will review recent progress in examining the molecular and biochemical properties of the different domains of the RECQ4 protein. We will shed light on how the dynamic roles of RECQ4 in human cells may contribute to the complexity of RECQ4 clinical phenotypes.

Environmental Thermal Stress Induces Neuronal Cell Death and Developmental Malformations in Reptiles

Every stage of organismal life history is being challenged by global warming. Many species are already experiencing temperatures approaching their physiological limits; this is particularly true for ectothermic species, such as lizards. Embryos are markedly sensitive to thermal insult. Here, we demonstrate that temperatures currently experienced in natural nesting areas can modify gene expression levels and induce neural and craniofacial malformations in embryos of the lizard Anolis sagrei. Developmental abnormalities ranged from minor changes in facial structure to significant disruption of anterior face and forebrain. The first several days of post-oviposition development are particularly sensitive to this thermal insult. These results raise new concern over the viability of ectothermic species under contemporary climate change. Herein, we propose and test a novel developmental hypothesis that describes the cellular and developmental origins of those malformations: cell death in the developing forebrain and disruption of normal facial induction due to disrupted Hedgehog signaling. Based on similarities in the embryonic response to thermal stress among distantly related species, we propose that this developmental hypothesis represents a common embryonic response to thermal insult among amniote embryos. Our results emphasize the importance of adopting a broad, multi-disciplinary approach that includes both lab and field perspectives when trying to understand the future impacts of anthropogenic change on animal development.

Wnt/β-Catenin-Dependent Transcription in Autism Spectrum Disorders

Autism spectrum disorders (ASD) is a heterogeneous group of neurodevelopmental disorders characterized by synaptic dysfunction and defects in dendritic spine morphology. In the past decade, an extensive list of genes associated with ASD has been identified by genome-wide sequencing initiatives. Several of these genes functionally converge in the regulation of the Wnt/β-catenin signaling pathway, a conserved cascade essential for stem cell pluripotency and cell fate decisions during development. Here, we review current information regarding the transcriptional program of Wnt/β-catenin signaling in ASD. First, we discuss that Wnt/β-catenin gain and loss of function studies recapitulate brain developmental abnormalities associated with ASD. Second, transcriptomic approaches using patient-derived induced pluripotent stem cells (iPSC) cells, featuring mutations in high confidence ASD genes, reveal a significant dysregulation in the expression of Wnt signaling components. Finally, we focus on the activity of chromatin-remodeling proteins and transcription factors considered high confidence ASD genes, including CHD8, ARID1B, ADNP, and TBR1, that regulate Wnt/β-catenin-dependent transcriptional activity in multiple cell types, including pyramidal neurons, interneurons and oligodendrocytes, cells which are becoming increasingly relevant in the study of ASD. We conclude that the level of Wnt/β-catenin signaling activation could explain the high phenotypical heterogeneity of ASD and be instrumental in the development of new diagnostics tools and therapies.

Neurochemical and Behavioral Consequences of Ethanol and/or Caffeine Exposure: Effects in Zebrafish and Rodents

: Zebrafish are increasingly being utilized to model the behavioral and neurochemical effects of pharmaceuticals and, more recently, pharmaceutical interactions. Zebrafish models of stress establish that both caffeine and ethanol influence anxiety, though few studies have implemented co-administration to assess the interaction of anxiety and reward-seeking. Caffeine exposure in zebrafish is teratogenic, causing developmental abnormalities in the cardiovascular, neuromuscular, and nervous systems of embryos and larvae. Ethanol is also a teratogen and, as an anxiolytic substance, may be able to offset the anxiogenic effects of caffeine. Co-exposure to caffeine and alcohol impacts neuroanatomy and behavior in adolescent animal models, suggesting stimulant substances may moderate the impact of alcohol on neural circuit development. Here, we review the literature describing neuropharmacological and behavioral consequences of caffeine and/or alcohol exposure in the zebrafish model, focusing on neurochemistry, locomotor effects, and behavioral assessments of stress/anxiety as reported in adolescent/juvenile and adult animals. The purpose of this review is twofold: (1) describe the work in zebrafish documenting the effects of ethanol and/or caffeine exposure and (2) compare these zebrafish studies with comparable experiments in rodents. We focus on specific neurochemical pathways (dopamine, serotonin, adenosine, GABA, adenosine), anxiety-type behaviors (assessed with novel tank, thigmotaxis, shoaling), and locomotor changes resulting from both individual and co-exposure. We compare findings in zebrafish with those in rodent models, revealing similarities across species and identifying conservation of mechanisms that potentially reinforce co-addiction.