A SMAD1/5-YAP signalling module drives radial glia self-amplification and growth of the developing cerebral cortex.

The growth and evolutionary expansion of the cerebral cortex are defined by the spatial-temporal production of neurons, which itself depends on the decision of radial glial cells (RGCs) to self-amplify or to switch to neurogenic divisions. The mechanisms regulating these RGC fate decisions are still incompletely understood. Here, we describe a novel and evolutionarily conserved role of the canonical BMP transcription factors SMAD1/5 in controlling neurogenesis and growth during corticogenesis. Reducing the expression of both SMAD1 and SMAD5 in neural progenitors at early mouse cortical development caused microcephaly and an increased production of early-born cortical neurons at the expense of late-born ones, which correlated with the premature differentiation and depletion of the pool of cortical progenitors. Gain- and loss-of-function experiments performed during early cortical neurogenesis in the chick revealed that SMAD1/5 activity supports self-amplifying RGC divisions and restrains the neurogenic ones. Furthermore, we demonstrate that SMAD1/5 stimulate RGC self-amplification through the positive post-transcriptional regulation of the Hippo signalling effector YAP. We anticipate this SMAD1/5-YAP signalling module to be fundamental in controlling growth and evolution of the amniote cerebral cortex.

DYRK1A modulates c-MET in pancreatic ductal adenocarcinoma to drive tumour growth.

BACKGROUND AND AIMS: Pancreatic ductal adenocarcinoma (PDAC) is a very aggressive tumour with a poor prognosis using current treatments. Targeted therapies may offer a new avenue for more effective strategies. Dual-specificity tyrosine regulated kinase 1A (DYRK1A) is a pleiotropic kinase with contradictory roles in different tumours that is uncharacterised in PDAC. Here, we aimed to investigate the role of DYRK1A in pancreatic tumorigenesis. DESIGN: We analysed DYRK1A expression in PDAC genetic mouse models and in patient samples. DYRK1A function was assessed with knockdown experiments in pancreatic tumour cell lines and in PDAC mouse models with genetic reduction of Dyrk1a dosage. Furthermore, we explored a mechanistic model for DYRK1A activity. RESULTS: We showed that DYRK1A was highly expressed in PDAC, and that its protein level positively correlated with that of c-MET. Inhibition of DYRK1A reduced tumour progression by limiting tumour cell proliferation. DYRK1A stabilised the c-MET receptor through SPRY2, leading to prolonged activation of extracellular signal-regulated kinase signalling. CONCLUSIONS: These findings reveal that DYRK1A contributes to tumour growth in PDAC, at least through regulation of c-MET accumulation, suggesting that inhibition of DYRK1A could represent a novel therapeutic target for PDAC.

Impaired development of neocortical circuits contributes to the neurological alterations in DYRK1A haploinsufficiency syndrome.

Autism spectrum disorders are early onset neurodevelopmental disorders characterized by deficits in social communication and restricted repetitive behaviors, yet they are quite heterogeneous in terms of their genetic basis and phenotypic manifestations. Recently, de novo pathogenic mutations in DYRK1A, a chromosome 21 gene associated to neuropathological traits of Down syndrome, have been identified in patients presenting a recognizable syndrome included in the autism spectrum. These mutations produce DYRK1A kinases with partial or complete absence of the catalytic domain, or they represent missense mutations located within this domain. Here, we undertook an extensive biochemical characterization of the DYRK1A missense mutations reported to date and show that most of them, but not all, result in enzymatically dead DYRK1A proteins. We also show that haploinsufficient Dyrk1a+/- mutant mice mirror the neurological traits associated with the human pathology, such as defective social interactions, stereotypic behaviors and epileptic activity. These mutant mice present altered proportions of excitatory and inhibitory neocortical neurons and synapses. Moreover, we provide evidence that alterations in the production of cortical excitatory neurons are contributing to these defects. Indeed, by the end of the neurogenic period, the expression of developmental regulated genes involved in neuron differentiation and/or activity is altered. Therefore, our data indicate that altered neocortical neurogenesis could critically affect the formation of cortical circuits, thereby contributing to the neuropathological changes in DYRK1A haploinsufficiency syndrome.

Triplication of DYRK1A causes retinal structural and functional alterations in Down syndrome.

Down syndrome (DS) results from the triplication of approximately 300 human chromosome 21 (Hsa21) genes and affects almost all body organs. Children with DS have defects in visual processing that may have a negative impact on their daily life and cognitive development. However, there is little known about the genes and pathogenesis underlying these defects. Here, we show morphometric in vivo data indicating that the neural retina is thicker in DS individuals than in the normal population. A similar thickening specifically affecting the inner part of the retina was also observed in a trisomic model of DS, the Ts65Dn mouse. Increased retinal size and cellularity in this model correlated with abnormal retinal function and resulted from an impaired caspase-9-mediated apoptosis during development. Moreover, we show that mice bearing only one additional copy of Dyrk1a have the same retinal phenotype as Ts65Dn mice and normalization of Dyrk1a gene copy number in Ts65Dn mice completely rescues both, morphological and functional phenotypes. Thus, triplication of Dyrk1a is necessary and sufficient to cause the retinal phenotype described in the trisomic model. Our data demonstrate for the first time the implication of DYRK1A overexpression in a developmental alteration of the central nervous system associated with DS, thereby providing insights into the aetiology of neurosensorial dysfunction in a complex disease.

Dyrk1a haploinsufficiency induces diabetes in mice through decreased pancreatic beta cell mass.

AIMS/HYPOTHESIS: Growth factors and nutrients are important regulators of pancreatic beta cell mass and function. However, the signalling pathways by which these factors modulate these processes have not yet been fully elucidated. DYRK1A (also named minibrain/MNB) is a member of the dual-specificity tyrosine phosphorylation-regulated kinase (DYRK) family that has been conserved across evolution. A significant amount of data implicates DYRK1A in brain growth and function, as well as in neurodegenerative processes in Alzheimer's disease and Down's syndrome. We investigated here whether DYRK1A would be an attractive candidate for beta cell growth modulation. METHODS: To study the role of DYRK1A in beta cell growth, we used Dyrk1a-deficient mice. RESULTS: We show that DYRK1A is expressed in pancreatic islets and provide evidence that changes in Dyrk1a gene dosage in mice strongly modulate glycaemia and circulating insulin levels. Specifically, Dyrk1a-haploinsufficient mice show severe glucose intolerance, reduced beta cell mass and decreased beta cell proliferation. CONCLUSIONS/INTERPRETATION: Taken together, our data indicate that DYRK1A is a critical kinase for beta cell growth as Dyrk1a-haploinsufficient mice show a diabetic profile.

Over-expression of RCAN1 causes Down syndrome-like hippocampal deficits that alter learning and memory.

People with Down syndrome (DS) exhibit abnormal brain structure. Alterations affecting neurotransmission and signalling pathways that govern brain function are also evident. A large number of genes are simultaneously expressed at abnormal levels in DS; therefore, it is a challenge to determine which gene(s) contribute to specific abnormalities, and then identify the key molecular pathways involved. We generated RCAN1-TG mice to study the consequences of RCAN1 over-expression and investigate the contribution of RCAN1 to the brain phenotype of DS. RCAN1-TG mice exhibit structural brain abnormalities in those areas affected in DS. The volume and number of neurons within the hippocampus is reduced and this correlates with a defect in adult neurogenesis. The density of dendritic spines on RCAN1-TG hippocampal pyramidal neurons is also reduced. Deficits in hippocampal-dependent learning and short- and long-term memory are accompanied by a failure to maintain long-term potentiation (LTP) in hippocampal slices. In response to LTP induction, we observed diminished calcium transients and decreased phosphorylation of CaMKII and ERK1/2-proteins that are essential for the maintenance of LTP and formation of memory. Our data strongly suggest that RCAN1 plays an important role in normal brain development and function and its up-regulation likely contributes to the neural deficits associated with DS.

Upregulation of RCAN1 causes Down syndrome-like immune dysfunction.

BACKGROUND: People with Down syndrome (DS) are more susceptible to infections and autoimmune disease, but the molecular genetic basis for these immune defects remains undetermined. In this study, we tested whether increased expression of the chromosome 21 gene RCAN1 contributes to immune dysregulation. METHODS: We investigated the immune phenotype of a mouse model that overexpresses RCAN1. RCAN1 transgenic (TG) mice exhibit T cell abnormalities that bear a striking similarity to the abnormalities described in individuals with DS. RESULTS: RCAN1-TG mice display T cell developmental defects in the thymus and peripheral immune tissues. Thymic cellularity is reduced by substantial losses of mature CD4 and CD8 thymocytes and medullary epithelium. In peripheral immune organs T lymphocytes are reduced in number and exhibit reduced proliferative capacity and aberrant cytokine production. These T cell defects are stem cell intrinsic in that transfer of wild type bone marrow into RCAN1-TG recipients restored medullary thymic epithelium and T cell numbers in the thymus, spleen and lymph nodes. However, bone marrow transplantation failed to improve T cell function, suggesting an additional role for RCAN1 in the non-haemopoietic compartment. CONCLUSIONS: RCAN1 therefore facilitates T cell development and function, and when overexpressed, may contribute to immune dysfunction in DS.

Gene expression analysis of the embryonic subplate.

The subplate layer of the cerebral cortex is comprised of a heterogeneous population of cells and contains some of the earliest-generated neurons. In the embryonic brain, subplate cells contribute to the guidance and areal targeting of thalamocortical axons. At later developmental stages, they are predominantly involved in the maturation and plasticity of the cortical circuitry and the establishment of functional modules. We aimed to further characterize the embryonic murine subplate population by establishing a gene expression profile at embryonic day (E) 15.5 using laser capture microdissection and microarrays. The microarray identified over 300 transcripts with higher expression in the subplate compared with the cortical plate at this stage. Using quantitative reverse transcription-polymerase chain reaction, in situ hybridization (ISH), and immunohistochemistry (IHC), we have confirmed specific expression in the E15.5 subplate for 13 selected genes, which have not been previously associated with this compartment (Abca8a, Cdh10, Cdh18, Csmd3, Gabra5, Kcnt2, Ogfrl1, Pls3, Rcan2, Sv2b, Slc8a2, Unc5c, and Zdhhc2). In the reeler mutant, the expression of the majority of these genes (9 of 13) was shifted in accordance with the altered position of subplate. These genes belong to several functional groups and likely contribute to synapse formation and axonal growth and guidance in subplate cells.

Impaired macroglial development and axonal conductivity contributes to the neuropathology of DYRK1A-related intellectual disability syndrome.

The correct development and activity of neurons and glial cells is necessary to establish proper brain connectivity. DYRK1A encodes a protein kinase involved in the neuropathology associated with Down syndrome that influences neurogenesis and the morphological differentiation of neurons. DYRK1A loss-of-function mutations in heterozygosity cause a well-recognizable syndrome of intellectual disability and autism spectrum disorder. In this study, we analysed the developmental trajectories of macroglial cells and the properties of the corpus callosum, the major white matter tract of the brain, in Dyrk1a+/- mice, a mouse model that recapitulates the main neurological features of DYRK1A syndrome. We found that Dyrk1a+/- haploinsufficient mutants present an increase in astrogliogenesis in the neocortex and a delay in the production of cortical oligodendrocyte progenitor cells and their progression along the oligodendroglial lineage. There were fewer myelinated axons in the corpus callosum of Dyrk1a+/- mice, axons that are thinner and with abnormal nodes of Ranvier. Moreover, action potential propagation along myelinated and unmyelinated callosal axons was slower in Dyrk1a+/- mutants. All these alterations are likely to affect neuronal circuit development and alter network synchronicity, influencing higher brain functions. These alterations highlight the relevance of glial cell abnormalities in neurodevelopmental disorders.

DSCR1/RCAN1 regulates vesicle exocytosis and fusion pore kinetics: implications for Down syndrome and Alzheimer's disease.

Genes located on chromosome 21, over-expressed in Down syndrome (DS) and Alzheimer's disease (AD) and which regulate vesicle trafficking, are strong candidates for involvement in AD neuropathology. Regulator of calcineurin activity 1 (RCAN1) is one such gene. We have generated mutant mice in which RCAN1 is either over-expressed (RCAN1(ox)) or ablated (Rcan1-/-) and examined whether exocytosis from chromaffin cells, a classic cellular model of neuronal exocytosis, is altered using carbon fibre amperometry. We find that Rcan1 regulates the number of vesicles undergoing exocytosis and the speed at which the vesicle fusion pore opens and closes. Cells from both Rcan1-/- and RCAN1(ox) mice display reduced levels of exocytosis. Changes in single-vesicle fusion kinetics are also evident resulting in the less catecholamine released per vesicle with increasing Rcan1 expression. Acute calcineurin inhibition did not replicate the effect of RCAN1 overexpression. These changes are not due to alterations in Ca2+ entry or the readily releasable vesicle pool size. Thus, we illustrate a novel regulator of vesicle exocytosis, Rcan1, which influences both exocytotic rate and vesicle fusion kinetics. If Rcan1 functions similarly in neurons then overexpression of this protein, as occurs in DS and AD brains, will reduce both the number of synaptic vesicles undergoing exocytosis and the amount of neurotransmitter released per fusion event. This has direct implications for the pathogenesis of these diseases as sufficient levels of neurotransmission are required for synaptic maintenance and the prevention of neurodegeneration and vesicle trafficking defects are the earliest hallmark of AD neuropathology.

Age-associated motor and visuo-spatial learning phenotype in Dyrk1A heterozygous mutant mice.

Dual-specificity tyrosine-regulated kinase 1A (DYRK1A) is a candidate gene for the Down syndrome neurological defects and may be involved in the progression of Alzheimer's disease. Heterozygous mice for Dyrk1A (Dyrk1A+/-) exhibit decreased brain size, motor abnormalities and cognitive deficits in the adult. However, there is no information about the mutant phenotype in old ages. Here we analyze the impact of Dyrk1A dosage reduction on motor performance and hippocampal-dependent learning and memory in aged Dyrk1A+/- mice. Whereas motor tests showed marked alterations in traction ability, prehensile reflex and balance, heterozygous mice only present a slight impairment of visuo-spatial memory even though they show a robust decrease of CA1-CA3 and dentate gyrus cells.

Automated Macro Approach to Quantify Synapse Density in 2D Confocal Images from Fixed Immunolabeled Neural Tissue Sections.

This chapter describes an ImageJ/Fiji automated macro approach to estimate synapse densities in 2D fluorescence confocal microscopy images. The main step-by-step imaging workflow is explained, including example macro language scripts that perform all steps automatically for multiple images. Such tool provides a straightforward method for exploratory synapse screenings where hundreds to thousands of images need to be analyzed in order to render significant statistical information. The method can be adapted to any particular set of images where fixed brain slices have been immunolabeled against validated presynaptic and postsynaptic markers.

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.

Efficient and specific transduction of cochlear supporting cells by adeno-associated virus serotype 5.

Congenital deafness, affecting 1 in 1000 neonates, can lead to major problems in speech, cognitive and psychosocial development. Congenital deafness is mainly caused by mutations in connexins, hemi-channel proteins forming gap-junctions between supporting cells in the sensory epithelia. We describe a high tropism of AAV5 serotype for the supporting cells of the cochlea, both in vitro in postnatal day 4 mouse explants, and in vivo in the adult guinea-pig inner ear, through scala media perfusion. AAV5 transduction correlates with PDGFRalpha expression, previously reported as AAV5 receptor. This vector could be of major interest in addressing gene therapy approaches to deafness as well as for studying basic aspects of inner-ear development and hearing mechanisms.

DYRK1A Kinase Positively Regulates Angiogenic Responses in Endothelial Cells.

Angiogenesis is a highly regulated process essential for organ development and maintenance, and its deregulation contributes to inflammation, cardiac disorders, and cancer. The Ca2+/nuclear factor of activated T cells (NFAT) signaling pathway is central to endothelial cell angiogenic responses, and it is activated by stimuli like vascular endothelial growth factor (VEGF) A. NFAT phosphorylation by dual-specificity tyrosine phosphorylation-regulated kinases (DYRKs) is thought to be an inactivating event. Contrary to expectations, we show that the DYRK family member DYRK1A positively regulates VEGF-dependent NFAT transcriptional responses in primary endothelial cells. DYRK1A silencing reduces intracellular Ca2+ influx in response to VEGF, which dampens NFAT activation. The effect is exerted at the level of VEGFR2 accumulation leading to impairment in PLCγ1 activation. Notably, Dyrk1a heterozygous mice show defects in developmental retinal vascularization. Our data establish a regulatory circuit, DYRK1A/ Ca2+/NFAT, to fine-tune endothelial cell proliferation and angiogenesis.

Dyrk1A haploinsufficiency affects viability and causes developmental delay and abnormal brain morphology in mice.

DYRK1A is the human orthologue of the Drosophila minibrain (mnb) gene, which is involved in postembryonic neurogenesis in flies. Because of its mapping position on chromosome 21 and the neurobehavioral alterations shown by mice overexpressing this gene, involvement of DYRK1A in some of the neurological defects of Down syndrome patients has been suggested. To gain insight into its physiological role, we have generated mice deficient in Dyrk1A function by gene targeting. Dyrk1A(-/-) null mutants presented a general growth delay and died during midgestation. Mice heterozygous for the mutation (Dyrk1A(+/-)) showed decreased neonatal viability and a significant body size reduction from birth to adulthood. General neurobehavioral analysis revealed preweaning developmental delay of Dyrk1A(+/-) mice and specific alterations in adults. Brains of Dyrk1A(+/-) mice were decreased in size in a region-specific manner, although the cytoarchitecture and neuronal components in most areas were not altered. Cell counts showed increased neuronal densities in some brain regions and a specific decrease in the number of neurons in the superior colliculus, which exhibited a significant size reduction. These data provide evidence about the nonredundant, vital role of Dyrk1A and suggest a conserved mode of action that determines normal growth and brain size in both mice and flies.

Expression profiles of the connexin genes, Gjb1 and Gjb3, in the developing mouse cochlea.

Several connexin genes (GJB1, GJB2, GJB3, GJB6 and GJA1) have been found mutated in patients with non-syndromic and/or syndromic deafness indicating an important role of these proteins in the auditory system. In order to better understand the function of the connexins in the inner ear we have analyzed the gene expression profiles of two connexin genes, Gjb1 (connexin 32) and Gjb3 (connexin 31), by in situ hybridization during the mouse cochlea organogenesis, from early otocyst up to the mature organ in adult. In the developing otocyst epithelium, some restricted domains expressed Gjb3 and Gjb1 whilst high levels of both transcripts were present in the surrounding mesenchymal tissue. As development proceeds, expression of these two genes was found in various subtypes of fibrocytes, either within the spiral limbus or along the spiral ligament, as well as in the basilar membrane cells, in the Reissner's membrane cells, and in subsets of the cellular elements of the cochlear ganglion. Gjb3 and Gjb1 expression was spatiotemporally modulated within the sensory hair cells and the various supporting cells that compose the developing organ of Corti. A transitory expression of Gjb1 was found in the basal and intermediate cells of the stria vascularis. In the adult cochlea Gjb1 transcripts disappeared while Gjb3 expression remained present in fibrocytes with specific expression patterns.

Abnormal mineralization of the Ts65Dn Down syndrome mouse appendicular skeleton begins during embryonic development in a Dyrk1a-independent manner.

The relationship between gene dosage imbalance and phenotypes associated with Trisomy 21, including the etiology of abnormal bone phenotypes linked to Down syndrome (DS), is not well understood. The Ts65Dn mouse model for DS exhibits appendicular skeletal defects during adolescence and adulthood but the developmental and genetic origin of these phenotypes remains unclear. It is hypothesized that the postnatal Ts65Dn skeletal phenotype originates during embryonic development and results from an increased Dyrk1a gene copy number, a gene hypothesized to play a critical role in many DS phenotypes. Ts65Dn embryos exhibit a lower percent bone volume in the E17.5 femur when compared to euploid embryos. Concomitant with gene copy number, qPCR analysis revealed a ~1.5 fold increase in Dyrk1a transcript levels in the Ts65Dn E17.5 embryonic femur as compared to euploid. Returning Dyrk1a copy number to euploid levels in Ts65Dn, Dyrk1a(+/-) embryos did not correct the trisomic skeletal phenotype but did return Dyrk1a gene transcript levels to normal. The size and protein expression patterns of the cartilage template during embryonic bone development appear to be unaffected at E14.5 and E17.5 in trisomic embryos. Taken together, these data suggest that the dosage imbalance of genes other than Dyrk1a is involved in the development of the prenatal bone phenotype in Ts65Dn embryos.

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.

Expression profiles of the connexin genes, Gjb1 and Gjb3, in the developing mouse cochlea.

Several connexin genes (GJB1, GJB2, GJB3, GJB6 and GJA1) have been found mutated in patients with non-syndromic and/or syndromic deafness indicating an important role of these proteins in the auditory system. In order to better understand the function of the connexins in the inner ear we have analyzed the gene expression profiles of two connexin genes, Gjb1 (connexin 32) and Gjb3 (connexin 31), by in situ hybridization during the mouse cochlea organogenesis, from early otocyst up to the mature organ in adult. In the developing otocyst epithelium, some restricted domains expressed Gjb3 and Gjb1 whilst high levels of both transcripts were present in the surrounding mesenchymal tissue. As development proceeds, expression of these two genes was found in various subtypes of fibrocytes, either within the spiral limbus or along the spiral ligament, as well as in the basilar membrane cells, in the Reissner's membrane cells, and in subsets of the cellular elements of the cochlear ganglion. Gjb3 and Gjb1 expression was spatiotemporally modulated within the sensory hair cells and the various supporting cells that compose the developing organ of Corti. A transitory expression of Gjb1 was found in the basal and intermediate cells of the stria vascularis. In the adult cochlea Gjb1 transcripts disappeared while Gjb3 expression remained present in fibrocytes with specific expression patterns.