Importance For Brain Development Research Articles

MerTK is a mediator of alpha-synuclein fibril uptake by human microglia.

Mer tyrosine kinase (MerTK) is a receptor tyrosine kinase that mediates non-inflammatory, homeostatic phagocytosis of diverse types of cellular debris. Highly expressed on the surface of microglial cells, MerTK is of importance in brain development, homeostasis, plasticity and disease. Yet, involvement of this receptor in the clearance of protein aggregates that accumulate with ageing and in neurodegenerative diseases has yet to be defined. The current study explored the function of MerTK in the microglial uptake of alpha-synuclein fibrils which play a causative role in the pathobiology of synucleinopathies. Using human primary and induced pluripotent stem cell-derived microglia, the MerTK-dependence of alpha-synuclein fibril internalization was investigated in vitro. Relevance of this pathway in synucleinopathies was assessed through burden analysis of MERTK variants and analysis of MerTK expression in patient-derived cells and tissues. Pharmacological inhibition of MerTK and siRNA-mediated MERTK knockdown both caused a decreased rate of alpha-synuclein fibril internalization by human microglia. Consistent with the non-inflammatory nature of MerTK-mediated phagocytosis, alpha-synuclein fibril internalization was not observed to induce secretion of pro-inflammatory cytokines such as IL-6 or TNF, and downmodulated IL-1β secretion from microglia. Burden analysis in two independent patient cohorts revealed a significant association between rare functionally deleterious MERTK variants and Parkinson's disease in one of the cohorts (P = 0.002). Despite a small upregulation in MERTK mRNA expression in nigral microglia from Parkinson's disease/Lewy body dementia patients compared to those from non-neurological control donors in a single-nuclei RNA-sequencing dataset (P = 5.08 × 10-21), no significant upregulation in MerTK protein expression was observed in human cortex and substantia nigra lysates from Lewy body dementia patients compared to controls. Taken together, our findings define a novel role for MerTK in mediating the uptake of alpha-synuclein fibrils by human microglia, with possible involvement in limiting alpha-synuclein spread in synucleinopathies such as Parkinson's disease. Upregulation of this pathway in synucleinopathies could have therapeutic values in enhancing alpha-synuclein fibril clearance in the brain.

Gustavson syndrome is caused by an in-frame deletion in RBMX associated with potentially disturbed SH3 domain interactions

RNA binding motif protein X‐linked (RBMX) encodes the heterogeneous nuclear ribonucleoprotein G (hnRNP G) that regulates splicing, sister chromatid cohesion and genome stability. RBMX knock down experiments in various model organisms highlight the gene’s importance for brain development. Deletion of the RGG/RG motif in hnRNP G has previously been associated with Shashi syndrome, however involvement of other hnRNP G domains in intellectual disability remain unknown. In the current study, we present the underlying genetic and molecular cause of Gustavson syndrome. Gustavson syndrome was first reported in 1993 in a large Swedish five-generation family presented with profound X-linked intellectual disability and an early death. Extensive genomic analyses of the family revealed hemizygosity for a novel in-frame deletion in RBMX in affected individuals (NM_002139.4; c.484_486del, p.(Pro162del)). Carrier females were asymptomatic and presented with skewed X-chromosome inactivation, indicating silencing of the pathogenic allele. Affected individuals presented minor phenotypic overlap with Shashi syndrome, indicating a different disease-causing mechanism. Investigation of the variant effect in a neuronal cell line (SH-SY5Y) revealed differentially expressed genes enriched for transcription factors involved in RNA polymerase II transcription. Prediction tools and a fluorescence polarization assay imply a novel SH3-binding motif of hnRNP G, and potentially a reduced affinity to SH3 domains caused by the deletion. In conclusion, we present a novel in-frame deletion in RBMX segregating with Gustavson syndrome, leading to disturbed RNA polymerase II transcription, and potentially reduced SH3 binding. The results indicate that disruption of different protein domains affects the severity of RBMX-associated intellectual disabilities.

Influence of Dietary Polar Lipid Supplementation on Memory and Longitudinal Brain Development.

Polar lipids, which are found in human milk, serve essential functions within biological membranes, hence their importance in brain development and cognition. Therefore, we aimed to evaluate the longitudinal effects on brain macrostructural and microstructural development and recognition memory of early-life polar lipid supplementation using the translational pig model. Twenty-eight intact (i.e., not castrated) male pigs were provided either a control diet (n = 14) or the control diet supplemented with polar lipids (n = 14) from postnatal day 2 until postnatal week 4. After postnatal week 4, all animals were provided the same nutritionally-adequate diets until postnatal week 24. Pigs underwent magnetic resonance imaging at 8 longitudinal time-points to model brain macrostructural and microstructural developmental trajectories. The novel object recognition task was implemented at postnatal weeks 4 and 8 to evaluate recognition memory. Subtle differences were observed between groups in hippocampal absolute brain volumes and fractional anisotropy, and no differences in myelin water fraction developmental patterns were noted. Behavioral outcomes did not differ in recognition memory, and only minimal differences were observed in exploratory behaviors. Our findings suggest that early-life dietary supplementation of polar lipids has limited effect on brain developmental patterns, object recognition memory, and exploratory behaviors.

Characterization of miRNA Isoform Expression In Schizophrenia Using Postmortem Human Brain Tissue

The nuances of small non-coding RNA biology continue to be discovered. The most characterized species of non-coding RNAs are microRNA (miRNA). miRNA largely function to modulate gene expression by repressing the translation of mRNA into protein. It is now known that miRNA participate in regulating nearly every type of cellular process and their importance in brain development, function, and disease continues to be uncovered. Recently RNA sequencing revealed that miRNA are often produced in detectable levels with slight sequence variations. Several steps are involved in the biogenesis of miRNA and slight changes in these processes can lead to a variety of extensions, deletions, or alterations in the final mature sequence. The name isomiR for these isoforms of canonically described miRNA sequences was coined in 2008. Research demonstrates that these miRNA variants have altered stability and in some cases distinct functions from their close sequence relatives. Recent findings also indicate that altered isomiR expression is associated with disease states. To date little research has characterized the expression of isomiRs in the brain, however alterations in canonical miRNA expression and miRNA biogenesis have been reproducibly associated with schizophrenia, suggesting that the biogenesis of isomiRs may also be altered. Therefore, we characterized isomiR expression in 92 postmortem dorsolateral prefrontal cortex (DLPFC) human brain samples, including 30 samples from patients with schizophrenia and 62 from healthy controls. Using small RNA sequencing, we profiled the expression of both canonical miRNAs and isomiRs. We utilized the BIOO Scientific NextFlex small RNA sequencing kit, with 500 ng of starting total RNA and ran 50 base pair sequencing on the HiSeq 3000. We achieved a sequencing depth of over 20 million reads per sample. Reads were aligned to miRNA and isomiR sequences using miRge. First, we assessed the overall magnitude and diversity of isomiR expression, however no differences were found between cases and controls. We then assessed the influence of diagnosis on the expression of individual miRNAs and isomiRs. Seven canonical miRNAs and 52 isomiRs, derived from 22 canonically described miRNA sequences, were identified to be differentially expressed between cases and controls. Importantly many of these isomiRs had alterations in the 5 prime portion of their sequence. Such alterations have been shown to shift the repertoire of binding partners to be distinct from that of the canonical sequence. Therefore, altered expression of these isomiRs may especially indicate modifications in gene expression regulation in schizophrenia. More research is necessary to decipher the role of these miRNA variants in schizophrenia and the brain. However, our study suggests that such variation should not be ignored.

Post-traumatic stress disorder symptom severity, trauma load and sleeping difficulties in trauma-exposed, treatment-seeking adolescents

IntroductionSleep disturbances are associated with various anxiety- and trauma-related disorders, and specifically with post-traumatic stress disorder (PTSD). Two of the core symptoms of PTSD are recurrent distressing dreams about the traumatic event and difficulty in falling or staying asleep (insomnia). Sleep is essential for functioning, with poor sleep compromising cognitive, emotional and behavioural regulations. Sleep is also of particular importance for brain development and information processing in children and adolescents. The aim of this study was to determine if PTSD symptom severity and trauma load is associated with nightmares and insomnia in a sample of trauma-exposed, treatment-seeking adolescents.MethodsA total of 358 South African adolescents, between 12 and 18 years of age, exposed to at least one DSM-5 qualifying traumatic event, were assessed for PTSD-related sleep difficulties using the Kiddie Schedule for Affective Disorders and Schizophrenia (KSADS). Childhood exposure to 10 common trauma types was also recorded using the KSADS trauma checklist. PTSD symptom severity was measured using the child PTSD checklist (CPC).ResultsAdolescents reporting current trauma-related nightmares (F[268.2] = 0.68, t = -8.16, p = 0.000) and current insomnia (F[265.2] = 0.16, t = -9.03, p = 0.000) had significantly higher PTSD symptom severity scores compared to those without current nightmares and insomnia. Adolescents with current trauma-related nightmares (F[355.2] = 0.15, t = -3.30, p = 0.001) and insomnia (F[353.2] = 0.15, t = -2.51, p = 0.013) were also exposed to a significantly greater number of different trauma types compared to those without current nightmares and insomnia.ConclusionAssessing and treating sleep difficulties related to PTSD in trauma-exposed adolescents, in an effort to reduce the developmental impact of trauma on the brain and general functioning, should not be overlooked. Longitudinal studies may contribute to a better understanding of the long-term effects of trauma-related insomnia and nightmares on mental and physical health outcomes.

N-3 (Omega-3) Fatty Acids: Effects on Brain Dopamine Systems and Potential Role in the Etiology and Treatment of Neuropsychiatric Disorders.

A number of neuropsychiatric disorders, including Parkinson's disease, schizophrenia, attention deficit hyperactivity disorder, and, to some extent, depression, involve dysregulation of the brain dopamine systems. The etiology of these diseases is multifactorial, involving genetic and environmental factors. Evidence suggests that inadequate levels of n-3 (omega- 3) polyunsaturated fatty acids (PUFA) in the brain may represent a risk factor for these disorders. These fatty acids, which are derived from the diet, are a major component of neuronal membranes and are of particular importance in brain development and function. Low levels of n-3 PUFAs in the brain affect the brain dopamine systems and, when combined with appropriate genetic and other factors, increase the risk of developing these disorders and/or the severity of the disease. This article reviews the neurobiology of n-3 PUFAs and their effects on dopaminergic function. Clinical studies supporting their role in the etiologies of diseases involving the brain dopamine systems and the potential of n-3 PUFAs in the treatment of these disorders are discussed.

Dystroglycan Maintains Inner Limiting Membrane Integrity to Coordinate Retinal Development.

Proper neural circuit formation requires the precise regulation of neuronal migration, axon guidance, and dendritic arborization. Mutations affecting the function of the transmembrane glycoprotein dystroglycan cause a form of congenital muscular dystrophy that is frequently associated with neurodevelopmental abnormalities. Despite its importance in brain development, the role of dystroglycan in regulating retinal development remains poorly understood. Using a mouse model of dystroglycanopathy (ISPDL79* ) and conditional dystroglycan mutants of both sexes, we show that dystroglycan is critical for the proper migration, axon guidance, and dendritic stratification of neurons in the inner retina. Using genetic approaches, we show that dystroglycan functions in neuroepithelial cells as an extracellular scaffold to maintain the integrity of the retinal inner limiting membrane. Surprisingly, despite the profound disruptions in inner retinal circuit formation, spontaneous retinal activity is preserved. These results highlight the importance of dystroglycan in coordinating multiple aspects of retinal development.SIGNIFICANCE STATEMENT The extracellular environment plays a critical role in coordinating neuronal migration and neurite outgrowth during neural circuit development. The transmembrane glycoprotein dystroglycan functions as a receptor for multiple extracellular matrix proteins and its dysfunction leads to a form of muscular dystrophy frequently associated with neurodevelopmental defects. Our results demonstrate that dystroglycan is required for maintaining the structural integrity of the inner limiting membrane (ILM) in the developing retina. In the absence of functional dystroglycan, ILM degeneration leads to defective migration, axon guidance, and mosaic spacing of neurons and a loss of multiple neuron types during retinal development. These results demonstrate that disorganization of retinal circuit development is a likely contributor to visual dysfunction in patients with dystroglycanopathy.

Neurodevelopment and Early Childhood Education for Low-Income Students: An Analytical Literature Review

A child's experiences shape his development and never is that more true than in his earliest years. The early childhood years are a time when student's brain is rapidly maturing. Educators must make every effort to ensure that at school, the experiences to which children are exposed and the resources to which they have access are positive. Considering both the importance of brain development in children’s early years and the disadvantages faced by our at-risk populations of children, it is imperative that educators consider what the study of neuroscience can contribute to the field of early childhood education. This review examines the overlap of neurology and early childhood experiences especially as it pertains to students of lower socioeconomic status. Three significant external factors that influence children’s neurodevelopment are discussed. These three influential factors are adult engagement, the home environment, and the school environment. Additionally, suggestions for future research will be proposed.

The involvement of heparan sulfate proteoglycans in stem cell differentiation and in malignant glioma

Heparan sulfate (HS) proteoglycans (HSPG) are major components of the extracellular matrix. They interact with a plethora of macromolecules that are of physiological importance. The pattern of sulfation of the HS chain determines the specificity of these interactions. The enzymes that synthesize and degrade HS are thus key regulators of processes ranging from embryonic development to tissue homeostasis and tumor development. Formation of the nervous system is also critically dependent on appropriate HSPGs as shown by several studies on the role of HS in neural induction from embryonic stem cells. High-grade glioma is the most common primary malignant brain tumor among adults, and the prognosis is poor. Neural and glioma stem cells share several traits, including sustained proliferation and highly efficient migration in the brain. There are also similarities between the neurogenic niche where adult neural stem cells reside and the tumorigenic niche, including their interactions with components of the extracellular matrix (ECM). The levels of many of these components, for example HSPGs and enzymes involved in the biosynthesis and modification of HS are attenuated in gliomas. In this paper, HS regulation of pathways involved in neural differentiation and how these may be of importance for brain development are discussed. The literature suggesting that modifications of HS could regulate glioma growth and invasion is reviewed. Targeting the invasiveness of glioma cells by modulating HS may improve upon present therapeutic options, which only marginally enhance the survival of glioma patients.

Transient receptor potential channels and their role in modulating radial glial-neuronal interaction: a signaling pathway involving mGluR5.

The guidance of developing neurons to the right position in the central nervous system is of central importance in brain development. Canonical transient receptor potential (TRPC) channels are thought to mediate turning responses of growth cones to guidance cues through fine control of calcium transients. Proliferating and 1- to 5-day-differentiated neural progenitor cells (NPCs) showed expression of Trpc1 and Trpc3 mRNA, while Trpc4-7 was not clearly detected. Time-lapse imaging showed that the motility pattern of neuronal cells was phasic with bursts of rapid movement (>60 μm/h), changes in direction, and intermittent slow phases or stallings (<40 μm/h), which frequently occurred in close contact with radial glial processes. Genetic interference with the TRPC3 and TRPC1 channel enhanced the motility of NPCs (burst frequency/stalling frequency). TRPC3-deficient cells or cells treated with the TRPC3 blocker pyr3 infrequently changed direction and seldom contacted radial glial processes. TRPC channels are also activated by group I metabotropic glutamate receptors (mGluR1 and mGluR5). As shown here, pyr3 blocked the calcium response mediated through mGluR5 in radial glial processes. Furthermore, 2-methyl-6-(phenylethynyl)pyridine, a blocker of mGluR5, affected the motility pattern in a similar way as TRPC3/6 double knockout or pyr3. The results suggest that radial glial cells exert attractant signals to migrating neuronal cells, which alter their motility pattern. Our results suggest that mGluR5 acting through TRPC3 is of central importance in radial glial-mediated neuronal guidance.

Tubulin glycylases and glutamylases have distinct functions in stabilization and motility of ependymal cilia

Microtubules are subject to a variety of posttranslational modifications that potentially regulate cytoskeletal functions. Two modifications, glutamylation and glycylation, are highly enriched in the axonemes of most eukaryotes, and might therefore play particularly important roles in cilia and flagella. Here we systematically analyze the dynamics of glutamylation and glycylation in developing mouse ependymal cilia and the expression of the corresponding enzymes in the brain. By systematically screening enzymes of the TTLL family for specific functions in ependymal cilia, we demonstrate that the glycylating enzymes TTLL3 and TTLL8 were required for stability and maintenance of ependymal cilia, whereas the polyglutamylase TTLL6 was necessary for coordinated beating behavior. Our work provides evidence for a functional separation of glutamylating and glycylating enzymes in mammalian ependymal cilia. It further advances the elucidation of the functions of tubulin posttranslational modifications in motile cilia of the mammalian brain and their potential importance in brain development and disease.

Identification of thyroid hormone response elements in vivo using mice expressing a tagged thyroid hormone receptor α1

TRα1 (thyroid hormone receptor α1) is well recognized for its importance in brain development. However, due to the difficulties in predicting TREs (thyroid hormone response elements) in silico and the lack of suitable antibodies against TRα1 for ChIP (chromatin immunoprecipitation), only a few direct TRα1 target genes have been identified in the brain. Here we demonstrate that mice expressing a TRα1–GFP (green fluorescent protein) fusion protein from the endogenous TRα locus provide a valuable animal model to identify TRα1 target genes. To this end, we analysed DNA–TRα1 interactions in vivo using ChIP with an anti-GFP antibody. We validated our system using established TREs from neurogranin and hairless, and by verifying additional TREs from known TRα1 target genes in brain and heart. Moreover, our model system enabled the identification of novel TRα1 target genes such as RNF166 (ring finger protein 166). Our results demonstrate that transgenic mice expressing a tagged nuclear receptor constitute a feasible approach to study receptor–DNA interactions in vivo, circumventing the need for specific antibodies. Models like the TRα1–GFP mice may thus pave the way for genome-wide mapping of nuclear receptor-binding sites, and advance the identification of novel target genes in vivo.

Docosahexaenoic Acid in Neural Signaling Systems

Docosahexaenoic acid has been conserved in neural signalling systems in the cephalopods, fish, amphibian, reptiles, birds, mammals, primates and humans. This extreme conservation, despite wide genomic changes over 500 million years, testifies to a uniqueness of this molecule in the brain. The brain selectively incorporates docosahexaenoic acid and its rate of incorporation into the developing brain has been shown to be greater than ten times more efficient than its synthesis from the omega 3 fatty acids of land plant origin. Data has now been published demonstrating a significant influence of dietary omega 3 fatty acids on neural gene expression. As docosahexaenoic acid is the only omega 3 fatty acid in the brain, it is likely that it is the ligand involved. The selective uptake, requirement for function and stimulation of gene expression would have conferred an advantage to a primate which separated from the chimpanzees in the forests and woodlands and sought a different ecological niche. In view of the paucity of docosahexaenoic acid in the land food chain it is likely that the advantage would have been gained from a lacustrine or marine coastal habitat with access to food rich in docosahexaenoic acid and the accessory micronutrients, such as iodine, zinc, copper, manganese and selenium, of importance in brain development and protection against peroxidation. Land agricultural development has, in recent time, come to dominate the human food chain. The decline in use and availability of aquatic resources is not considered important by Langdon (2006) as he considers the resource was not needed for human evolution and can be replaced from the terrestrial food chain. This notion is not supported by the biochemistry nor the molecular biology. He misses the point that the shoreline hypothesis is not just dependent on docosahexaenoic acid but also on the other accessory nutrients specifically required by the brain. Moreover he neglects the basic principle of Darwinian evolution. The well documented greater efficiency of preformed docosahexaenoic acid for brain incorporation during development would have conferred a distinct survival advantage over those without it. All terrestrial mammals lost brain capacity in relation to advancing increase in body size. The rise in mental ill health and brain disorders, to replace all other costs in the European list of burdens of ill health, (Andlin Sobocki et al., 2005) raises interesting questions as to its association with the reduced availability and consumption of marine and fresh water products. The threat posed by the continued rise in brain disorders also raises questions of importance to present and future food and agricultural policies.

Role of dystrophin and utrophin for assembly and function of the dystrophin glycoprotein complex in non-muscle tissue.

The dystrophin glycoprotein complex (DGC) is a multimeric protein assembly associated with either the X-linked cytoskeletal protein dystrophin or its autosomal homologue utrophin. In striated muscle cells, the DGC links the extracellular matrix to the actin cytoskeleton and mediates three major functions: structural stability of the plasma membrane, ion homeostasis, and transmembrane signaling. Mutations affecting the DGC underlie major forms of congenital muscle dystrophies. The DGC is prominent also in the central and peripheral nervous system and in tissues with a secretory function or which form barriers between functional compartments, such as the blood-brain barrier, choroid plexus, or kidney. A considerable molecular heterogeneity arises from cell-specific expression of its constituent proteins, notably short C-terminal isoforms of dystrophin. Experimentally, the generation of mice carrying targeted gene deletions affecting the DGC has clarified the interdependence of DGC proteins for assembly of the complex and revealed its importance for brain development and regulation of the 'milieu intérieur. Here, we focus on recent studies of the DGC in brain, blood-brain barrier and choroid plexus, retina, and kidney and discuss the role of dystrophin isoforms and utrophin for assembly of the complex in these tissues.

Exon 2 of the gene for neural cell adhesion molecule L1 is alternatively spliced in B cells.

L1CAM is a neural cell adhesion molecule expressed mainly on neurones' cell surface and plays an important role in the developing fetal brain. Recently, we have shown that mutations in the gene encoding L1CAM are responsible for three related neurological disorders including the most common form of inherited hydrocephalus. During our genetic analysis, we have discovered that L1CAM is also expressed on the surface of B cells but that the messenger RNA in this tissue is different to that in brain through alternative splicing of the L1 gene. This indicates that this region of the L1 molecule has a distinct role in brain cells compared to B lymphocytes and confirms its importance in brain development.