Increased dosage of DYRK1A and DSCR1 delays neuronal differentiation in neocortical progenitor cells

Neocortical neuronal production and maturation defects in the TcMAC21 mouse model of Down syndrome

Down syndrome (DS) results from trisomy of human chromosome 21 (HSA21), and DS research has been conducted by the use of mouse models. We previously generated a humanized mouse model of DS, TcMAC21, which carries the long arm of HSA21. These mice exhibit learning and memory deficits, and may reproduce neurodevelopmental alterations observed in humans with DS. Here, we performed histologic studies of the TcMAC21 forebrain from embryonic to adult stages. The TcMAC21 neocortex showed reduced proliferation of neural progenitors and delayed neurogenesis. These abnormalities were associated with a smaller number of projection neurons and interneurons. Further, (phospho-)proteomic analysis of adult TcMAC21 cortex revealed alterations in the phosphorylation levels of a series of synaptic proteins. The TcMAC21 mouse model shows similar brain development abnormalities as DS, and will be a valuable model to investigate prenatal and postnatal causes of intellectual disability in humans with DS.

Biphasic cell cycle defect causes impaired neurogenesis in down syndrome

Impaired neurogenesis in Down syndrome (DS) is characterized by reduced neurons, increased glial cells, and delayed cortical lamination. However, the underlying cause for impaired neurogenesis in DS is not clear. Using both human and mouse iPSCs, we demonstrate that DS impaired neurogenesis is due to biphasic cell cycle dysregulation during the generation of neural progenitors from iPSCs named the “neurogenic stage” of neurogenesis. Upon neural induction, DS cells showed reduced proliferation during the early phase followed by increased proliferation in the late phase of the neurogenic stage compared to control cells. While reduced proliferation in the early phase causes reduced neural progenitor pool, increased proliferation in the late phase leads to delayed post mitotic neuron generation in DS. RNAseq analysis of late-phase DS progenitor cells revealed upregulation of S phase-promoting regulators, Notch, Wnt, Interferon pathways, and REST, and downregulation of several genes of the BAF chromatin remodeling complex. NFIB and POU3F4, neurogenic genes activated by the interaction of PAX6 and the BAF complex, were downregulated in DS cells. ChIPseq analysis of late-phase neural progenitors revealed aberrant PAX6 binding with reduced promoter occupancy in DS cells. Together, these data indicate that impaired neurogenesis in DS is due to biphasic cell cycle dysregulation during the neurogenic stage of neurogenesis.

The Challenging Pathway of Treatment for Neurogenesis Impairment in Down Syndrome: Achievements and Perspectives

Down syndrome (DS), also known as trisomy 21, is a genetic disorder caused by triplication of Chromosome 21. Gene triplication may compromise different body functions but invariably impairs intellectual abilities starting from infancy. Moreover, after the fourth decade of life people with DS are likely to develop Alzheimer’s disease. Neurogenesis impairment during fetal life stages and dendritic pathology emerging in early infancy are thought to be key determinants of alterations in brain functioning in DS. Although the progressive improvement in medical care has led to a notable increase in life expectancy for people with DS, there are currently no treatments for intellectual disability. Increasing evidence in mouse models of DS reveals that pharmacological interventions in the embryonic and neonatal periods may greatly benefit brain development and cognitive performance. The most striking results have been obtained with pharmacotherapies during embryonic life stages, indicating that it is possible to pharmacologically rescue the severe neurodevelopmental defects linked to the trisomic condition. These findings provide hope that similar benefits may be possible for people with DS. This review summarizes current knowledge regarding (i) the scope and timeline of neurogenesis (and dendritic) alterations in DS, in order to delineate suitable windows for treatment; (ii) the role of triplicated genes that are most likely to be the key determinants of these alterations, in order to highlight possible therapeutic targets; and (iii) prenatal and neonatal treatments that have proved to be effective in mouse models, in order to rationalize the choice of treatment for human application. Based on this body of evidence we will discuss prospects and challenges for fetal therapy in individuals with DS as a potential means of drastically counteracting the deleterious effects of gene triplication.

A plant-specific DYRK kinase DYRKP coordinates cell morphology in Marchantia polymorpha

Dual-specificity tyrosine phosphorylation-regulated kinases (DYRKs) are activated via the auto-phosphorylation of conserved tyrosine residues in their activation loop during protein translation, and they then phosphorylate serine/threonine residues on substrates. The DYRK family is widely conserved in eukaryotes and is composed of six subgroups. In plant lineages, DYRK homologs are classified into four subgroups, DYRK2s, yet another kinase1s, pre-mRNA processing factor 4 kinases, and DYRKPs. Only the DYRKP subgroup is plant-specific and has been identified in a wide array of plant lineages, including land plants and green algae. It has been suggested that in Arabidopsis thaliana DYRKPs are involved in the regulation of centripetal nuclear positioning induced by dark light conditions. However, the molecular functions, such as kinase activity and the developmental and physiological roles of DYRKPs are poorly understood. Here, we focused on a sole DYRKP ortholog in the model bryophyte, Marchantia polymorpha, MpDYRKP. MpDYRKP has a highly conserved kinase domain located in the C-terminal region and shares common sequence motifs in the N-terminal region with other DYRKP members. To identify the roles of MpDYRKP in M. polymorpha, we generated loss-of-function Mpdyrkp mutants via genome editing. Mpdyrkp mutants exhibited abnormal, shrunken morphologies with less flattening in their vegetative plant bodies, thalli, and male reproductive organs, antheridial receptacles. The surfaces of the thalli in the Mpdyrkp mutants appeared uneven and disordered. Moreover, their epidermal cells were drastically altered to a narrower shape when compared to the wild type. These results suggest that MpDYRKP acts as a morphological regulator, which contributes to orderly tissue morphogenesis via the regulation of cell shape.

MAP kinase/ERK kinase 1 (MEK1) phosphorylates regulator of calcineurin 1 (RCAN1) to regulate neuronal differentiation

Regulator of calcineurin 1 (RCAN1) is located close to the Down syndrome critical region (DSCR) on human chromosome 21 and is related to the Down syndrome (DS) phenotype. To identify a novel binding partner of RCAN1, we performed yeast two-hybrid screening and identified mitogen-activated protein (MAP) kinase/extracellular signal-regulated kinase (ERK) kinase 1 (MEK1) as a partner. MEK1 was able to bind and phosphorylate RCAN1 in vitro and in vivo. MEK1-dependent RCAN1 phosphorylation caused an increase in RCAN1 expression by increasing the protein half-life. Nerve growth factor (NGF)-dependent activation of the MEK1 pathway consistently induced RCAN1 expression. Moreover, we found that RCAN1 overexpression inhibited NGF-induced neurite outgrowth and expression of neuronal marker genes, such as growth cone-associated protein 43 (GAP43) and synapsin I, via inhibition of MEK1-ERK1/2 pathways. Our findings provide evidence that MEK1-dependent RCAN1 phosphorylation acts as an important molecular mechanism in the control of neuronal differentiation.

Genes Associated with Disturbed Cerebral Neurogenesis in the Embryonic Brain of Mouse Models of Down Syndrome

Down syndrome (DS), also known as trisomy 21, is the most frequent genetic cause of intellectual disability. Although the mechanism remains unknown, delayed brain development is assumed to be involved in DS intellectual disability. Analyses with human with DS and mouse models have shown that defects in embryonic cortical neurogenesis may lead to delayed brain development. Cre-loxP-mediated chromosomal engineering has allowed the generation of a variety of mouse models carrying various partial Mmu16 segments. These mouse models are useful for determining genotype–phenotype correlations and identifying dosage-sensitive genes involved in the impaired neurogenesis. In this review, we summarize several candidate genes and pathways that have been linked to defective cortical neurogenesis in DS.

A Multiplex Human Pluripotent Stem Cell Platform Defines Molecular and Functional Subclasses of Autism-Related Genes

Autism is a clinically heterogeneous neurodevelopmental disorder characterized by impaired social interactions, restricted interests, and repetitive behaviors. Despite significant advances in the genetics of autism, understanding how genetic changes perturb brain development and affect clinical symptoms remains elusive. Here, we present a multiplex human pluripotent stem cell (hPSC) platform, in which 30 isogenic disease lines are pooled in a single dish and differentiated into prefrontal cortex (PFC) lineages to efficiently test early-developmental hypotheses of autism. We define subgroups of autism mutations that perturb PFC neurogenesis and are correlated to abnormal WNT/βcatenin responses. Class 1 mutations (8 of 27) inhibit while class 2 mutations (5 of 27) enhance PFC neurogenesis. Remarkably, autism patient data reveal that individuals carrying subclass-specific mutations differ clinically in their corresponding language acquisition profiles. Our study provides a framework to disentangle genetic heterogeneity associated with autism and points toward converging molecular and developmental pathways of diverse autism-associated mutations.

DYRK1A Negatively Regulates CDK5-SOX2 Pathway and Self-Renewal of Glioblastoma Stem Cells

Glioblastoma display vast cellular heterogeneity, with glioblastoma stem cells (GSCs) at the apex. The critical role of GSCs in tumour growth and resistance to therapy highlights the need to delineate mechanisms that control stemness and differentiation potential of GSC. Dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) regulates neural progenitor cell differentiation, but its role in cancer stem cell differentiation is largely unknown. Herein, we demonstrate that DYRK1A kinase is crucial for the differentiation commitment of glioblastoma stem cells. DYRK1A inhibition insulates the self-renewing population of GSCs from potent differentiation-inducing signals. Mechanistically, we show that DYRK1A promotes differentiation and limits stemness acquisition via deactivation of CDK5, an unconventional kinase recently described as an oncogene. DYRK1A-dependent inactivation of CDK5 results in decreased expression of the stemness gene SOX2 and promotes the commitment of GSC to differentiate. Our investigations of the novel DYRK1A-CDK5-SOX2 pathway provide further insights into the mechanisms underlying glioblastoma stem cell maintenance.

Signalling Pathways Implicated in Alzheimer's Disease Neurodegeneration in Individuals with and without Down Syndrome

Down syndrome (DS), the most common cause of intellectual disability of genetic origin, is characterized by alterations in central nervous system morphology and function that appear from early prenatal stages. However, by the fourth decade of life, all individuals with DS develop neuropathology identical to that found in sporadic Alzheimer's disease (AD), including the development of amyloid plaques and neurofibrillary tangles due to hyperphosphorylation of tau protein, loss of neurons and synapses, reduced neurogenesis, enhanced oxidative stress, and mitochondrial dysfunction and neuroinflammation. It has been proposed that DS could be a useful model for studying the etiopathology of AD and to search for therapeutic targets. There is increasing evidence that the neuropathological events associated with AD are interrelated and that many of them not only are implicated in the onset of this pathology but are also a consequence of other alterations. Thus, a feedback mechanism exists between them. In this review, we summarize the signalling pathways implicated in each of the main neuropathological aspects of AD in individuals with and without DS as well as the interrelation of these pathways.

Regulator of Calcineurin (RCAN): Beyond Down Syndrome Critical Region

The regulator of calcineurin (RCAN) was first reported as a novel gene called DSCR1, encoded in a region termed the Down syndrome critical region (DSCR) of human chromosome 21. Genome sequence comparisons across species using bioinformatics revealed three members of the RCAN gene family, RCAN1, RCAN2, and RCAN3, present in most jawed vertebrates, with one member observed in most invertebrates and fungi. RCAN is most highly expressed in brain and striated muscles, but expression has been reported in many other tissues, as well, including the heart and kidneys. Expression levels of RCAN homologs are responsive to external stressors such as reactive oxygen species, Ca2+, amyloid β, and hormonal changes and upregulated in pathological conditions, including Alzheimer's disease, cardiac hypertrophy, diabetes, and degenerative neuropathy. RCAN binding to calcineurin, a Ca2+/calmodulin-dependent phosphatase, inhibits calcineurin activity, thereby regulating different physiological events via dephosphorylation of important substrates. Novel functions of RCANs have recently emerged, indicating involvement in mitochondria homeostasis, RNA binding, circadian rhythms, obesity, and thermogenesis, some of which are calcineurin-independent. These developments suggest that besides significant contributions to DS pathologies and calcineurin regulation, RCAN is an important participant across physiological systems, suggesting it as a favorable therapeutic target.

Complex chromosomal rearrangements of human chromosome 21 in a patient manifesting clinical features partially overlapped with that of Down syndrome

The chromosomal region critical in Down syndrome has long been analyzed through genotype-phenotype correlation studies using data from many patients with partial trisomy 21. Owing to that, a relatively small region of human chromosome 21 (35.9 ~ 38.0 Mb) has been considered as Down syndrome critical region (DSCR). In this study, microarray-based comparative genomic hybridization analysis identified complex rearrangements of chromosome 21 in a patient manifesting clinical features partially overlapped with that of Down syndrome. Although the patient did not show up-slanting palpebral fissures and single transverse palmar creases, other symptoms were consistent with Down syndrome. Rearrangements were analyzed by whole-genome sequencing using Nanopore long-read sequencing. The analysis revealed that chromosome 21 was fragmented into seven segments and reassembled by six connected points. Among 12 breakpoints, 5 are located within the short region and overlapped with repeated segments. The rearrangement resulted in a maximum gain of five copies, but no region showed loss of genomic copy numbers. Breakpoint-junctions showed no homologous region. Based on these findings, chromoanasynthesis was considered as the mechanism. Although the distal 21q22.13 region was not included in the aberrant regions, some of the genes located on the duplicated regions, SOD1, SON, ITSN1, RCAN1, and RUNX1, were considered as possible candidate genes for clinical features of the patient. We discussed the critical region for Down syndrome, with the literature review.

A Munc18-1 mutant mimicking phosphorylation by Down Syndrome-related kinase Dyrk1a supports normal synaptic transmission and promotes recovery after intense activity

Phosphorylation of Munc18-1 (Stxbp1), a presynaptic organizer of synaptic vesicle fusion, is a powerful mechanism to regulate synaptic strength. Munc18-1 is a proposed substrate for the Down Syndrome-related kinase dual-specificity tyrosine phosphorylation-regulate kinase 1a (Dyrk1a) and mutations in both genes cause intellectual disability. However, the functional consequences of Dyrk1a-dependent phosphorylation of Munc18-1 for synapse function are unknown. Here, we show that the proposed Munc18-1 phosphorylation site, T479, is among the highly constrained phosphorylation sites in the coding regions of the gene and is also located within a larger constrained coding region. We confirm that Dyrk1a phosphorylates Munc18-1 at T479. Patch-clamp physiology in conditional null mutant hippocampal neurons expressing Cre and either wildtype, or mutants mimicking or preventing phosphorylation, revealed that synaptic transmission is similar among the three groups: frequency/amplitude of mEPSCs, evoked EPSCs, paired pulse plasticity, rundown kinetics upon intense activity and the readily releasable pool. However, synapses expressing the phosphomimic mutant responded to intense activity with more pronounced facilitation. These data indicate that Dyrk1a-dependent Munc18-1 phosphorylation has a minor impact on synaptic transmission, only after intense activity, and that the role of genetic variation in both genes in intellectual disability may be through different mechanisms.

Aberrant Oligodendrogenesis in Down Syndrome: Shift in Gliogenesis?

Down syndrome (DS), or trisomy 21, is the most prevalent chromosomal anomaly accounting for cognitive impairment and intellectual disability (ID). Neuropathological changes of DS brains are characterized by a reduction in the number of neurons and oligodendrocytes, accompanied by hypomyelination and astrogliosis. Recent studies mainly focused on neuronal development in DS, but underestimated the role of glial cells as pathogenic players. Aberrant or impaired differentiation within the oligodendroglial lineage and altered white matter functionality are thought to contribute to central nervous system (CNS) malformations. Given that white matter, comprised of oligodendrocytes and their myelin sheaths, is vital for higher brain function, gathering knowledge about pathways and modulators challenging oligodendrogenesis and cell lineages within DS is essential. This review article discusses to what degree DS-related effects on oligodendroglial cells have been described and presents collected evidence regarding induced cell-fate switches, thereby resulting in an enhanced generation of astrocytes. Moreover, alterations in white matter formation observed in mouse and human post-mortem brains are described. Finally, the rationale for a better understanding of pathways and modulators responsible for the glial cell imbalance as a possible source for future therapeutic interventions is given based on current experience on pro-oligodendroglial treatment approaches developed for demyelinating diseases, such as multiple sclerosis.

Multiple functions of DYRK2 in cancer and tissue development

Dual-specificity tyrosine-regulated kinases (DYRKs) are evolutionarily conserved from yeast to mammals. Accumulating studies have revealed that DYRKs have important roles in regulation of the cell cycle and survival. DYRK2, a member of the class II DYRK family protein, is a key regulator of p53, and phosphorylates it at Ser46 to induce apoptosis in response to DNA damage. Moreover, recent studies have uncovered that DYRK2 regulates G1/S transition, epithelial-mesenchymal-transition, and stemness in human cancer cells. DYRK2 also appears to have roles in tissue development in lower eukaryotes. Thus, the elucidation of mechanisms for DYRK2 during mammalian tissue development will promote the understanding of cell differentiation, tissue homeostasis, and congenital diseases as well as cancer. In this review, we discuss the roles of DYRK2 in tumor cells. Moreover, we focus on DYRK2-dependent developmental mechanisms in several species including fly (Drosophila), worm (Caenorhabditis elegans), zebrafish (Danio rerio), and mammals.

Modeling Down syndrome in animals from the early stage to the 4.0 models and next

The genotype-phenotype relationship and the physiopathology of Down Syndrome (DS) have been explored in the last 20 years with more and more relevant mouse models. From the early age of transgenesis to the new CRISPR/CAS9-derived chromosomal engineering and the transchromosomic technologies, mouse models have been key to identify homologous genes or entire regions homologous to the human chromosome 21 that are necessary or sufficient to induce DS features, to investigate the complexity of the genetic interactions that are involved in DS and to explore therapeutic strategies. In this review we report the new developments made, how genomic data and new genetic tools have deeply changed our way of making models, extended our panel of animal models, and increased our understanding of the neurobiology of the disease. But even if we have made an incredible progress which promises to make DS a curable condition, we are facing new research challenges to nurture our knowledge of DS pathophysiology as a neurodevelopmental disorder with many comorbidities during ageing.

DSCR1-mediated TET1 splicing regulates miR-124 expression to control adult hippocampal neurogenesis

Whether epigenetic factors such as DNA methylation and microRNAs interact to control adult hippocampal neurogenesis is not fully understood. Here, we show that Down syndrome critical region 1 (DSCR1) protein plays a key role in adult hippocampal neurogenesis by modulating two epigenetic factors: TET1 and miR-124. We find that DSCR1 mutant mice have impaired adult hippocampal neurogenesis. DSCR1 binds to TET1 introns to regulate splicing of TET1, thereby modulating TET1 level. Furthermore, TET1 controls the demethylation of the miRNA-124 promoter to modulate miR-124 expression. Correcting the level of TET1 in DSCR1 knockout mice is sufficient to prevent defective adult neurogenesis. Importantly, restoring DSCR1 level in a Down syndrome mouse model effectively rescued adult neurogenesis and learning and memory deficits. Our study reveals that DSCR1 plays a critical upstream role in epigenetic regulation of adult neurogenesis and provides insights into potential therapeutic strategy for treating cognitive defects in Down syndrome.

Perturbation of the immune cells and prenatal neurogenesis by the triplication of the Erg gene in mouse models of Down syndrome

Some mouse models of Down syndrome (DS), including Ts1Cje mice, exhibit impaired prenatal neurogenesis with yet unknown molecular mechanism. To gain insights into the impaired neurogenesis, a transcriptomic and flow cytometry analysis of E14.5 Ts1Cje embryo brain was performed. Our analysis revealed that the neutrophil and monocyte ratios in the CD45-positive hematopoietic cells were relatively increased, in agreement with the altered expression of inflammation/immune-related genes, in Ts1Cje embryonic brain, whereas the relative number of brain macrophages was decreased in comparison to wild-type mice. Similar upregulation of inflammation-associated mRNAs was observed in other DS mouse models, with variable trisomic region lengths. We used genetic manipulation to assess the contribution of Erg, a trisomic gene in these DS models, known to regulation hemato-immune cells. The perturbed proportions of immune cells in Ts1Cje mouse brain were restored in Ts1Cje-Erg^+/+/Mld2 mice, which are disomic for functional Erg but otherwise trisomic on a Ts1Cje background. Moreover, the embryonic neurogenesis defects observed in Ts1Cje cortex were reduced in Ts1Cje-Erg^+/+/Mld2 embryos. Our findings suggest that Erg gene triplication contributes to the dysregulation of the homeostatic proportion of the populations of immune cells in the embryonic brain and decreased prenatal cortical neurogenesis in the prenatal brain with DS.

DYRK1A and cognition: A lifelong relationship

The dosage of the serine threonine kinase DYRK1A is critical in the central nervous system (CNS) during development and aging. This review analyzes the functions of this kinase by considering its interacting partners and pathways. The role of DYRK1A in controlling the differentiation of prenatal newly formed neurons is presented separately from its role at the pre- and post-synaptic levels in the adult CNS; its effects on synaptic plasticity are also discussed. Because this kinase is positioned at the crossroads of many important processes, genetic dosage errors in this protein produce devastating effects arising from DYRK1A deficiency, such as in MRD7, an autism spectrum disorder, or from DYRK1A excess, such as in Down syndrome. Effects of these errors have been shown in various animal models including Drosophila, zebrafish, and mice. Dysregulation of DYRK1A levels also occurs in neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. Finally, this review describes inhibitors that have been assessed in vivo. Accurate targeting of DYRK1A levels in the brain, with either inhibitors or activators, is a future research challenge.

Triple play of DYRK1A kinase in cortical progenitor cells of Trisomy 21

Down syndrome (DS) also known as Trisomy 21 is a genetic disorder that occurs in ∼1 in 800 live births. The disorder is caused by the triplication of all or part of human chromosome 21 and therefore, is thought to arise from the increased dosage of genes found within chromosome 21. The manifestations of the disease include among others physical growth delays and intellectual disability. A prominent anatomical feature of DS is the microcephaly that results from altered brain development. Recent studies using mouse models of DS have shed new light on DYRK1A (dual-specificity tyrosine-phosphorylation-regulated kinase 1A), a gene located on human chromosome 21 that plays a critical role in neocortical development. The present review summarizes effects of the increased dosage of DYRK1A on the proliferative, neurogenic and astrogliogenic potentials of cortical neural progenitor cells, and relates these findings to the clinical manifestations of the disease.

Autonomous trisomic rescue of Down syndrome cells

Down syndrome is the most frequent chromosomal abnormality among live-born infants. All Down syndrome patients have mental retardation and are prone to develop early onset Alzheimer's disease. However, it has not yet been elucidated whether there is a correlation between the phenotype of Down syndrome and the extra chromosome 21. In this study, we continuously cultivated induced pluripotent stem cells (iPSCs) with chromosome 21 trisomy for more than 70 weeks, and serendipitously obtained revertant cells with normal chromosome 21 diploids from the trisomic cells during long-term cultivation. Repeated experiments revealed that this trisomy rescue was not due to mosaicism of chromosome 21 diploid cells and occurred at an extremely high frequency. We herewith report the spontaneous correction from chromosome 21 trisomy to disomy without genetic manipulation, chemical treatment or exposure to irradiation. The revertant diploid cells will possibly serve a reference for drug screening and a raw material of regenerative medicinal products for cell-based therapy.

Altered development of dopaminergic neurons differentiated from stem cells from human exfoliated deciduous teeth of a patient with Down syndrome

Background

Down syndrome (DS) is a common developmental disorder resulting from the presence of an additional copy of chromosome 21. Abnormalities in dopamine signaling are suggested to be involved in cognitive dysfunction, one of the symptoms of DS, but the pathophysiological mechanism has not been fully elucidated at the cellular level. Stem cells from human exfoliated deciduous teeth (SHED) can be prepared from the dental pulp of primary teeth. Importantly, SHED can be collected noninvasively, have multipotency, and differentiate into dopaminergic neurons (DN). Therefore, we examined dopamine signaling in DS at the cellular level by isolating SHED from a patient with DS, differentiating the cells into DN, and examining development and function of DN.

Methods

Here, SHED were prepared from a normal participant (Ctrl-SHED) and a patient with DS (DS-SHED). Initial experiments were performed to confirm the morphological, chromosomal, and stem cell characteristics of both SHED populations. Next, Ctrl-SHED and DS-SHED were differentiated into DN and morphological analysis of DN was examined by immunostaining. Functional analysis of DN was performed by measuring extracellular dopamine levels under basal and glutamate-stimulated conditions. In addition, expression of molecules involved in dopamine homeostasis was examined by quantitative real-time polymerase chain reaction and immunostaining. Statistical analysis was performed using two-tailed Student’s t-tests.

Results

Compared with Ctrl-SHED, DS-SHED showed decreased expression of nestin, a neural stem-cell marker. Further, DS-SHED differentiated into DN (DS-DN) exhibiting decreased neurite outgrowth and branching compared with Ctrl-DN. In addition, DS-DN dopamine secretion was lower than Ctrl-DN dopamine secretion. Moreover, aberrant expression of molecules involved in dopaminergic homeostasis was observed in DS-DN.

Conclusions

Our results suggest that there was developmental abnormality and DN malfunction in the DS-SHED donor in this study. In the future, to clarify the detailed mechanism of dopamine-signal abnormality due to DN developmental and functional abnormalities in DS, it is necessary to increase the number of patients for analysis. Non-invasively harvested SHED may be very useful in the analysis of DS pathology.

Electronic supplementary material

The online version of this article (10.1186/s12883-018-1140-2) contains supplementary material, which is available to authorized users.

Muscle stem cell dysfunction impairs muscle regeneration in a mouse model of Down syndrome

Down syndrome, caused by trisomy 21, is characterized by a variety of medical conditions including intellectual impairments, cardiovascular defects, blood cell disorders and pre-mature aging phenotypes. Several somatic stem cell populations are dysfunctional in Down syndrome and their deficiencies may contribute to multiple Down syndrome phenotypes. Down syndrome is associated with muscle weakness but skeletal muscle stem cells or satellite cells in Down syndrome have not been investigated. We find that a failure in satellite cell expansion impairs muscle regeneration in the Ts65Dn mouse model of Down syndrome. Ts65Dn satellite cells accumulate DNA damage and over express Usp16, a histone de-ubiquitinating enzyme that regulates the DNA damage response. Impairment of satellite cell function, which further declines as Ts65Dn mice age, underscores stem cell deficiencies as an important contributor to Down syndrome pathologies.

Autism-associated Dyrk1a truncation mutants impair neuronal dendritic and spine growth and interfere with postnatal cortical development

Autism is a prevailing neurodevelopmental disorder with a large genetic/genomic component. Recently, the dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 1 A (DYRK1A) gene was implicated as a risk factor for autism spectrum disorder (ASD). We identified five DYRK1A variants in ASD patients and found that the dose of DYRK1A protein has a crucial role in various aspects of postnatal neural development. Dyrk1a loss of function and gain of function led to defects in dendritic growth, dendritic spine development and radial migration during cortical development. Importantly, two autism-associated truncations, R205X and E239X, were shown to be Dyrk1a loss-of-function mutants. Studies of the truncated Dyrk1a mutants may provide new insights into the role of Dyrk1a in brain development, as well as the role of Dyrk1a loss of function in the pathophysiology of autism.

DYRK1A Is a Regulator of S-Phase Entry in Hepatic Progenitor Cells

Hepatic progenitor cells (HPCs) are adult liver stem cells that act as second line of defense in liver regeneration. They are normally quiescent, but in case of severe liver damage, HPC proliferation is triggered by external activation mechanisms from their niche. Although several important proproliferative mechanisms have been described, it is not known which key intracellular regulators govern the switch between HPC quiescence and active cell cycle. We performed a high-throughput kinome small interfering RNA (siRNA) screen in HepaRG cells, a HPC-like cell line, and evaluated the effect on proliferation with a 5-ethynyl-2'-deoxyuridine (EdU) incorporation assay. One hit increased the percentage of EdU-positive cells after knockdown: dual specificity tyrosine phosphorylation regulated kinase 1A (DYRK1A). Although upon DYRK1A silencing, the percentage of EdU- and phosphorylated histone H3 (pH3)-positive cells was increased, and total cell numbers were not increased, possibly through a subsequent delay in cell cycle progression. This phenotype was confirmed with chemical inhibition of DYRK1A using harmine and with primary HPCs cultured as liver organoids. DYRK1A inhibition impaired Dimerization Partner, RB-like, E2F, and multivulva class B (DREAM) complex formation in HPCs and abolished its transcriptional repression on cell cycle progression. To further analyze DYRK1A function in HPC proliferation, liver organoid cultures were established from mBACtgDyrk1A mice, which harbor one extra copy of the murine Dyrk1a gene (Dyrk+++). Dyrk+++ organoids had both a reduced percentage of EdU-positive cells and reduced proliferation compared with wild-type organoids. This study provides evidence for an essential role of DYRK1A as balanced regulator of S-phase entry in HPCs. An exact gene dosage is crucial, as both DYRK1A deficiency and overexpression affect HPC cell cycle progression.

Neurogenesis impairment: An early developmental defect in Down syndrome

Down syndrome (DS) is characterized by brain hypotrophy and intellectual disability starting from early life stages. Accumulating evidence shows that the phenotypic features of the DS brain can be traced back to the fetal period since the DS brain exhibits proliferation potency reduction starting from the critical time window of fetal neurogenesis. This defect is worsened by the fact that neural progenitor cells exhibit reduced acquisition of a neuronal phenotype and an increase in the acquisition of an astrocytic phenotype. Consequently, the DS brain has fewer neurons in comparison with the typical brain. Although apoptotic cell death may be increased in DS, this does not seem to be the major cause of brain hypocellularity. Evidence obtained in brains of individuals with DS, DS-derived induced pluripotent stem cells (iPSCs), and DS mouse models has provided some insight into the mechanisms underlying the developmental defects due to the trisomic condition. Although many triplicated genes may be involved, in the light of the studies reviewed here, DYRK1A, APP, RCAN1 and OLIG1/2 appear to be particularly important determinants of many neurodevelopmental alterations that characterize DS because their triplication affects both the proliferation and fate of neural precursor cells as well as apoptotic cell death. Based on the evidence reviewed here, pathways downstream to these genes may represent strategic targets, for the design of possible interventions.

Dual-specificity tyrosine-phosphorylation regulated kinase 1A Gene Transcription is regulated by Myocyte Enhancer Factor 2D

Dual-specificity tyrosine-phosphorylation regulated kinase 1A (DYRK1A) is localized in the Down syndrome critical region of chromosome 21. As a candidate gene responsible for learning defects associated with Down syndrome and Alzheimer's disease (AD), DYRK1A has been implied to play pivotal roles in cell proliferation and brain development. MEF2D, a member of the myocyte-specific enhancer factor 2 (MEF2) family of transcription factors, was proved to be in control of neuronal cell differentiation and development. Here we demonstrated that MEF2D could upregulate DYRK1A gene expression through specific activation of DYRK1A isoform 5 gene transcription. A MEF2D responsive element from -268 to -254 bp on promoter region of DYRK1A isoform 5 was identified and confirmed by luciferase assay, electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP). The coordinated expression of DYRK1A and MEF2D in mouse brain development indicated a possibility of the cross-interaction of these two genes during neurodevelopment. The DYRK1A kinase activity was also affected by MEF2D's transcriptional regulation of DYRK1A. Therefore, the molecular regulation of DYRK1A by MEF2D further supported their involvement in neurodevelopment.

A small pons as a characteristic finding in Down syndrome: A quantitative MRI study

BACKGROUND

Down syndrome (DS) is the most common chromosomal aberration, but the characteristics of the brainstem component in this condition during childhood (from newborn to preteen stages) have not been clarified.

OBJECTIVE

To evaluate the morphological features of the brainstem in DS on magnetic resonance imaging (MRI).

MATERIALS AND METHODS

MRIs for 32 children with DS (16 boys and girls each; age range, 0-11years) without major brain insults, and 32 age-matched controls (16 boys and girls each) were retrospectively analyzed. Height, width, and area of the midbrain, pons, and medulla oblongata were measured on sagittal T1-weighted images; these were compared in children with DS and age-matched controls. The ratios of the brainstem to the size of the posterior fossa (BS/PF index) were calculated; these were also compared in the children with DS and the control group.

RESULTS

The width and area of the midbrain; height, width, area of the pons; and area of the medulla oblongata were significantly smaller in children with DS than in control children (P<0.05); the area of the pons, particularly for the ventral part, showed the largest differences in the mean relative differences. The BS/PF indices of the height, width, and area of the pons were significantly smaller in children with DS than in the control group (P<0.01). However, the BS/PF indices for the midbrain and the medulla oblongata did not differ between these two groups.

CONCLUSIONS

Children with DS may have small brainstems, particularly in the pons; this may be a characteristic morphological feature of the brainstem on MRI in childhood including neonates.

Molecular Mechanism Underlying Abnormal Differentiation of Neural Progenitor Cells in the Developing Down Syndrome Brain

Down syndrome (DS) is caused by trisomy for human chromosome 21. Individuals with DS commonly exhibit mental retardation, which is associated with abnormal brain development. In the neocortex of the DS brain, the density of neurons is markedly reduced, whereas that of astrocytes is increased. Similar to abnormalities seen in DS brains, mouse models of DS show deficits in brain development, and neural progenitor cells that give rise to neurons and glia show dysregulation in their differentiation. These suggest that the dysregulation of progenitor fate choices contributes to alterations in the numbers of neurons and astrocytes in the DS brain. Nevertheless, the molecular basis underlying these defects remains largely unknown. We showed that the overexpression of two human chromosome 21 genes, DYRK1A and DSCR1, contributes to suppressed neuronal differentiation of progenitors in the Ts1Cje mouse model of DS. In addition, the effect of DYRK1A and DSCR1 overexpression on neuronal differentiation is mediated by excessive attenuation of the transcription factor NFATc. Additionally, we demonstrated that an increased dosage of DYRK1A contributes to elevated potential of Ts1Cje progenitors to differentiate into astrocytes and enhanced astrogliogenesis in the Ts1Cje neocortex. Further, we linked the increased dosage of DYRK1A to dysregulation of STAT, a transcription factor critical for astrogliogenesis. Together, our studies identify critical pathways responsible for the proper differentiation of neural progenitors into neurons and astrocytes, with direct implications for the anomalies in brain development observed in DS.

Harmine stimulates proliferation of human neural progenitors

Harmine is the β-carboline alkaloid with the highest concentration in the psychotropic plant decoction Ayahuasca. In rodents, classical antidepressants reverse the symptoms of depression by stimulating neuronal proliferation. It has been shown that Ayahuasca presents antidepressant effects in patients with depressive disorder. In the present study, we investigated the effects of harmine in cell cultures containing human neural progenitor cells (hNPCs, 97% nestin-positive) derived from pluripotent stem cells. After 4 days of treatment, the pool of proliferating hNPCs increased by 71.5%. Harmine has been reported as a potent inhibitor of the dual specificity tyrosine-phosphorylation-regulated kinase (DYRK1A), which regulates cell proliferation and brain development. We tested the effect of analogs of harmine, an inhibitor of DYRK1A (INDY), and an irreversible selective inhibitor of monoamine oxidase (MAO) but not DYRK1A (pargyline). INDY but not pargyline induced proliferation of hNPCs similarly to harmine, suggesting that inhibition of DYRK1A is a possible mechanism to explain harmine effects upon the proliferation of hNPCs. Our findings show that harmine enhances proliferation of hNPCs and suggest that inhibition of DYRK1A may explain its effects upon proliferation in vitro and antidepressant effects in vivo.

Generation of improved human cerebral organoids from single copy DYRK1A knockout induced pluripotent stem cells in trisomy 21: hypothetical solutions for neurodevelopmental models and therapeutic alternatives in down syndrome

Dual-specificity thyrosine phosphorylation-regulated kinase 1A (DYRK1A) is a strong therapeutic target to ameliorate cognitive functions of Down Syndrome (DS). Genetic normalization of Dyrk1a is sufficient to normalize early cortical developmental phenotypes in DS mouse models. Gyrencephalic human neocortical development is more complex than that in lissencephalic mice; hence, cerebral organoids (COs) can be used to model early neurodevelopmental defects of DS. Single copy DYRK1A knockout COs (scDYRK1AKO-COs) can be generated from manipulated DS derived (DS-) induced pluripotent stem cells (iPSCs) and genetic normalization of DYRK1A is expected to result in corrected neurodevelopmental phenotypes that can be reminiscent of normal COs. DYRK1A knock-in (DYRK1AKI) COs can be derived after genetic manipulations of normal iPSCs and would be valuable to evaluate impaired neocortical development as can be seen in DS-COs. DYRK1A mutations cause severe human primary microcephaly; hence, dose optimization studies of DYRK1A inhibitors will be critical for prenatal therapeutic applications in DS. Several doses of DYRK1A inhibitors can be tested in the neurodevelopment process of DS-COs and DS-scDYRK1AKO-COs would be used as optimum models for evaluating phenotypic ameliorations. Overdose drug exposure in DS-COs can be explained by similar defects present in DS-baDYRK1AKO-COs and DYRK1AKO-COs. There are several limitations in the current CO technology, which can be reduced by the generation of vascularized brain-like organoids giving opportunities to mimic late-stage corticogenesis and complete hippocampal development. In the future, improved DS-DYRK1AKO-COs can be efficient in studies that aim to generate efficiently transplantable and implantable neurons for tissue regeneration alternatives in DS individuals.

Allele-Specific Phenotype Suggests a Possible Stimulatory Activity of RCAN-1 on Calcineurin in Caenorhabditis elegans

Regulator of calcineurin 1 (RCAN1) binds to calcineurin through the PxIxIT motif, which is evolutionarily conserved. SP repeat phosphorylation in RCAN1 is required for its complete function. The specific interaction between RCAN1 and calcineurin is critical for calcium/calmodulin-dependent regulation of calcineurin serine/threonine phosphatase activity. In this study, we investigated two available deletion rcan-1 mutants in Caenorhabditis elegans, which proceed differently for transcription and translation. We found that rcan-1 may be required for calcineurin activity and possess calcineurin-independent function in body growth and egg-laying behavior. In the genetic background of enhanced calcineurin activity, the rcan-1 mutant expressing a truncated RCAN-1 which retains the calcineurin-binding PxIxIT motif but misses SP repeats stimulated growth, while rcan-1 lack mutant resulted in hyperactive egg-laying suppression. These data suggest rcan-1 has unknown functions independent of calcineurin, and may be a stimulatory calcineurin regulator under certain circumstances.

Rad51 and Rad54 promote noncrossover recombination between centromere repeats on the same chromatid to prevent isochromosome formation

Centromeres consist of DNA repeats in many eukaryotes. Non-allelic homologous recombination (HR) between them can result in gross chromosomal rearrangements (GCRs). In fission yeast, Rad51 suppresses isochromosome formation that occurs between inverted repeats in the centromere. However, how the HR enzyme prevents homology-mediated GCRs remains unclear. Here, we provide evidence that Rad51 with the aid of the Swi/Snf-type motor protein Rad54 promotes non-crossover recombination between centromere repeats to prevent isochromosome formation. Mutations in Rad51 and Rad54 epistatically increased the rates of isochromosome formation and chromosome loss. In sharp contrast, these mutations decreased gene conversion between inverted repeats in the centromere. Remarkably, analysis of recombinant DNAs revealed that rad51 and rad54 increase the proportion of crossovers. In the absence of Rad51, deletion of the structure-specific endonuclease Mus81 decreased both crossovers and isochromosomes, while the cdc27/pol32-D1 mutation, which impairs break-induced replication, did not. We propose that Rad51 and Rad54 promote non-crossover recombination between centromere repeats on the same chromatid, thereby suppressing crossover between non-allelic repeats on sister chromatids that leads to chromosomal rearrangements. Furthermore, we found that Rad51 and Rad54 are required for gene silencing in centromeres, suggesting that HR also plays a role in the structure and function of centromeres.

DYRK1A, a Dosage-Sensitive Gene Involved in Neurodevelopmental Disorders, Is a Target for Drug Development in Down Syndrome

Down syndrome (DS) is one of the leading causes of intellectual disability, and patients with DS face various health issues, including learning and memory deficits, congenital heart disease, Alzheimer's disease (AD), leukemia, and cancer, leading to huge medical and social costs. Remarkable advances on DS research have been made in improving cognitive function in mouse models for future therapeutic approaches in patients. Among the different approaches, DYRK1A inhibitors have emerged as promising therapeutics to reduce DS cognitive deficits. DYRK1A is a dual-specificity kinase that is overexpressed in DS and plays a key role in neurogenesis, outgrowth of axons and dendrites, neuronal trafficking and aging. Its pivotal role in the DS phenotype makes it a prime target for the development of therapeutics. Recently, disruption of DYRK1A has been found in Autosomal Dominant Mental Retardation 7 (MRD7), resulting in severe mental deficiency. Recent advances in the development of kinase inhibitors are expected, in the near future, to remove DS from the list of incurable diseases, providing certain conditions such as drug dosage and correct timing for the optimum long-term treatment. In addition the exact molecular and cellular mechanisms that are targeted by the inhibition of DYRK1A are still to be discovered.

The G protein-coupled receptor GPR157 regulates neuronal differentiation of radial glial progenitors through the Gq-IP3 pathway

The ability of radial glial progenitors (RGPs) to generate cortical neurons is determined by local extracellular factors and signaling pathways intrinsic to RGPs. Here we find that GPR157, an orphan G protein-coupled receptor, localizes to RGPs’ primary cilia exposed to the cerebrospinal fluid (CSF). GPR157 couples with Gq-class of the heterotrimeric G-proteins and signals through IP₃-mediated Ca²⁺ cascade. Activation of GPR157-Gq signaling enhances neuronal differentiation of RGPs whereas interfering with GPR157-Gq-IP₃ cascade in RGPs suppresses neurogenesis. We also detect the presence of putative ligand(s) for GPR157 in the CSF, and demonstrate the increased ability of the CSF to activate GPR157 at neurogenic phase. Thus, GPR157-Gq signaling at the primary cilia of RGPs is activated by the CSF and contributes to neurogenesis.

DYRK1A overexpression enhances STAT activity and astrogliogenesis in a Down syndrome mouse model

Down syndrome (DS) arises from triplication of genes on human chromosome 21 and is associated with anomalies in brain development such as reduced production of neurons and increased generation of astrocytes. Here, we show that differentiation of cortical progenitor cells into astrocytes is promoted by DYRK1A, a Ser/Thr kinase encoded on human chromosome 21. In the Ts1Cje mouse model of DS, increased dosage of DYRK1A augments the propensity of progenitors to differentiate into astrocytes. This tendency is associated with enhanced astrogliogenesis in the developing neocortex. We also find that overexpression of DYRK1A upregulates the activity of the astrogliogenic transcription factor STAT in wild-type progenitors. Ts1Cje progenitors exhibit elevated STAT activity, and depletion of DYRK1A in these cells reverses the deregulation of STAT. In sum, our findings indicate that potentiation of the DYRK1A-STAT pathway in progenitors contributes to aberrant astrogliogenesis in DS.

DYRK1A-mediated Cyclin D1 Degradation in Neural Stem Cells Contributes to the Neurogenic Cortical Defects in Down Syndrome

Alterations in cerebral cortex connectivity lead to intellectual disability and in Down syndrome, this is associated with a deficit in cortical neurons that arises during prenatal development. However, the pathogenic mechanisms that cause this deficit have not yet been defined. Here we show that the human DYRK1A kinase on chromosome 21 tightly regulates the nuclear levels of Cyclin D1 in embryonic cortical stem (radial glia) cells, and that a modest increase in DYRK1A protein in transgenic embryos lengthens the G1 phase in these progenitors. These alterations promote asymmetric proliferative divisions at the expense of neurogenic divisions, producing a deficit in cortical projection neurons that persists in postnatal stages. Moreover, radial glial progenitors in the Ts65Dn mouse model of Down syndrome have less Cyclin D1, and Dyrk1a is the triplicated gene that causes both early cortical neurogenic defects and decreased nuclear Cyclin D1 levels in this model. These data provide insights into the mechanisms that couple cell cycle regulation and neuron production in cortical neural stem cells, emphasizing that the deleterious effect of DYRK1A triplication in the formation of the cerebral cortex begins at the onset of neurogenesis, which is relevant to the search for early therapeutic interventions in Down syndrome.

Tox: a multifunctional transcription factor and novel regulator of mammalian corticogenesis

Major efforts are invested to characterize the factors controlling the proliferation of neural stem cells. During mammalian corticogenesis, our group has identified a small pool of genes that are transiently downregulated in the switch of neural stem cells to neurogenic division and reinduced in newborn neurons. Among these switch genes, we found Tox, a transcription factor with hitherto uncharacterized roles in the nervous system. Here, we investigated the role of Tox in corticogenesis by characterizing its expression at the tissue, cellular and temporal level. We found that Tox is regulated by calcineurin/Nfat signalling. Moreover, we combined DNA adenine methyltransferase identification (DamID) with deep sequencing to characterize the chromatin binding properties of Tox including its motif and downstream transcriptional targets including Sox2, Tbr2, Prox1 and other key factors. Finally, we manipulated Tox in the developing brain and validated its multiple roles in promoting neural stem cell proliferation and neurite outgrowth of newborn neurons. Our data provide a valuable resource to study the role of Tox in other tissues and highlight a novel key player in brain development.

The Down syndrome-related protein kinase DYRK1A phosphorylates p27(Kip1) and Cyclin D1 and induces cell cycle exit and neuronal differentiation

A fundamental question in neurobiology is how the balance between proliferation and differentiation of neuronal precursors is maintained to ensure that the proper number of brain neurons is generated. Substantial evidence implicates DYRK1A (dual specificity tyrosine-phosphorylation-regulated kinase 1A) as a candidate gene responsible for altered neuronal development and brain abnormalities in Down syndrome. Recent findings support the hypothesis that DYRK1A is involved in cell cycle control. Nonetheless, how DYRK1A contributes to neuronal cell cycle regulation and thereby affects neurogenesis remains poorly understood. In the present study we have investigated the mechanisms by which DYRK1A affects cell cycle regulation and neuronal differentiation in a human cell model, mouse neurons, and mouse brain. Dependent on its kinase activity and correlated with the dosage of overexpression, DYRK1A blocked proliferation of SH-SY5Y neuroblastoma cells within 24 h and arrested the cells in G₁ phase. Sustained overexpression of DYRK1A induced G₀ cell cycle exit and neuronal differentiation. Furthermore, we provide evidence that DYRK1A modulated protein stability of cell cycle-regulatory proteins. DYRK1A reduced cellular Cyclin D1 levels by phosphorylation on Thr286, which is known to induce proteasomal degradation. In addition, DYRK1A phosphorylated p27(Kip1) on Ser10, resulting in protein stabilization. Inhibition of DYRK1A kinase activity reduced p27(Kip1) Ser10 phosphorylation in cultured hippocampal neurons and in embryonic mouse brain. In aggregate, these results suggest a novel mechanism by which overexpression of DYRK1A may promote premature neuronal differentiation and contribute to altered brain development in Down syndrome.