Nuclear Reorganization in Hippocampal Granule Cell Neurons from a Mouse Model of Down Syndrome: Changes in Chromatin Configuration, Nucleoli and Cajal Bodies

Down syndrome (DS) or trisomy of chromosome 21 (Hsa21) is characterized by impaired hippocampal-dependent learning and memory. These alterations are due to defective neurogenesis and to neuromorphological and functional anomalies of numerous neuronal populations, including hippocampal granular cells (GCs). It has been proposed that the additional gene dose in trisomic cells induces modifications in nuclear compartments and on the chromatin landscape, which could contribute to some DS phenotypes. The Ts65Dn (TS) mouse model of DS carries a triplication of 92 genes orthologous to those found in Hsa21, and shares many phenotypes with DS individuals, including cognitive and neuromorphological alterations. Considering its essential role in hippocampal memory formation, we investigated whether the triplication of this set of Hsa21 orthologous genes in TS mice modifies the nuclear architecture of their GCs. Our results show that the TS mouse presents alterations in the nuclear architecture of its GCs, affecting nuclear compartments involved in transcription and pre-rRNA and pre-mRNA processing. In particular, the GCs of the TS mouse show alterations in the nucleolar fusion pattern and the molecular assembly of Cajal bodies (CBs). Furthermore, hippocampal GCs of TS mice present an epigenetic dysregulation of chromatin that results in an increased heterochromatinization and reduced global transcriptional activity. These nuclear alterations could play an important role in the neuromorphological and/or functional alterations of the hippocampal GCs implicated in the cognitive dysfunction characteristic of TS mice.

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Ts65Dn, a Mouse Model of Down Syndrome, Exhibits Increased GABAB-Induced Potassium Current

Journal of Neurophysiology ◽

10.1152/jn.00626.2006 ◽

2007 ◽

Vol 97 (1) ◽

pp. 892-900 ◽

Cited By ~ 74

Author(s):

Tyler K. Best ◽

Richard J. Siarey ◽

Zygmunt Galdzicki

Keyword(s):

Down Syndrome ◽

Mouse Model ◽

Hippocampal Neurons ◽

Single Channel ◽

Extra Chromosome ◽

Functional Expression ◽

Chromosome 21 ◽

Fluctuation Analysis ◽

Response Curves ◽

Girk Channel

Down syndrome (DS) is the most common nonheritable cause of mental retardation. DS is the result of the presence of an extra chromosome 21 and its phenotype may be a consequence of overexpressed genes from that chromosome. One such gene is Kcnj6/Girk2, which encodes the G-protein-coupled inward rectifying potassium channel subunit 2 (GIRK2). We have recently shown that the DS mouse model, Ts65Dn, overexpresses GIRK2 throughout the brain and in particular the hippocampus. Here we report that this overexpression leads to a significant increase (∼2-fold) in GABAB-mediated GIRK current in primary cultured hippocampal neurons. The dose response curves for peak and steady-state GIRK current density is significantly shifted left toward lower concentrations of baclofen in Ts65Dn neurons compared with diploid controls, consistent with increased functional expression of GIRK channels. Stationary fluctuation analysis of baclofen-induced GIRK current from Ts65Dn neurons indicated no significant change in single-channel conductance compared with diploid. However, significant increases in GIRK channel density was found in Ts65Dn neurons. In normalized baclofen-induced GIRK current and GIRK current kinetics no difference was found between diploid and Ts65Dn neurons, which suggests unimpaired mechanisms of interaction between GIRK channel and GABAB receptor. These results indicate that increased expression of GIRK2 containing channels have functional consequences that likely affect the balance between excitatory and inhibitory neuronal transmission.

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A Myeloproliferative Disorder in the Tc1 Mouse Model of Down Syndrome

Blood ◽

10.1182/blood.v112.11.2790.2790 ◽

2008 ◽

Vol 112 (11) ◽

pp. 2790-2790

Author(s):

Kate A. Alford ◽

Lesley Vanes ◽

Zhe Li ◽

Stuart H. Orkin ◽

Elizabeth M. C. Fisher ◽

...

Keyword(s):

Down Syndrome ◽

Mouse Model ◽

Extramedullary Hematopoiesis ◽

Myeloproliferative Disorder ◽

Chromosome 21 ◽

Gene Encoding ◽

Megakaryoblastic Leukemia ◽

Cell Counts ◽

Hematopoietic Disorders

Abstract Down syndrome (DS) children have a one in ten chance of being diagnosed with leukemia within the first ten years of life. Acute megakaryoblastic leukemia (AMKL) is a subtype of acute myeloid leukemia (AML) that accounts for nearly 50% of these leukemias. AMKL is associated with a self-regressing neoplasia found almost exclusively in DS newborns called Transient Myeloproliferative Disorder (TMD). In all cases of TMD and DS-AMKL, leukemic blast cells show mutations in the gene encoding the hematopoietic transcription factor GATA1, resulting in production of a truncated form of the protein called GATA1s. Mutations in GATA1 are not seen in non-DS-AMKL or other DS leukemias and it is clear both trisomy of human chromosome 21 (HSA21) and a mutation in GATA1 are required for the development of both TMD and AMKL. However, it is unknown which genes on HSA21 need to be trisomic in order to predispose an individual with DS to AMKL. Our group has generated mice (termed the Tc1 mice) that contain an almost complete, freely segregating copy of HSA21. These mice display phenotypic features of DS. We have examined adult hematopoiesis in these mice. Blood samples taken from a cohort of Tc1 mice were examined from 4 weeks until 60 weeks of age. Complete blood cell counts show that whilst the mice do not develop leukemia they displayed persistent macrocytosis and had reduced erythrocyte numbers. Crossing the Tc1 mice with mice that express GATA1s protein did not perturb or exacerbate this phenotype. Over the age of 15 months more than 50% of Tc1 mice examined were found to have developed splenomegaly. These mice displayed megakaryocyte hyperplasia and had increased numbers of cells of the erythroid lineage. In vitro colony forming assays demonstrated an increase in the frequency of megakaryocytic and granulocyte-macrophage progenitors in the spleen, consistent with extramedullary hematopoiesis. In the bone marrow, no abnormalities were seen in the lineage-, c-Kit+, Sca1+ (LSK) compartment, however there was a significant increase in the percentage of common myeloid progenitors (CMP) and a corresponding decrease in megakaryocyte-erythrocyte progenitors (MEP). This suggests a possible block in development from CMP to MEP. These data demonstrate defects in hematopoietic development in a proportion of adult Tc1 mice. However, preliminary data suggest that these mice do not develop a neonatal myeloproliferative disorder that is comparable with human TMD. It may be that the phenotype seen in the adult Tc1 mice is due to defects in hematopoietic progenitors that are different to those responsible for development of TMD and DS-AMKL. This mouse model may therefore provide a useful tool to examine the role of HSA21 genes in adult hematopoietic disorders.

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Neurodevelopmental wiring deficits in the Ts65Dn mouse model of Down syndrome

10.1101/784314 ◽

2019 ◽

Author(s):

Shruti Jain ◽

Christina A. Watts ◽

Wilson C.J. Chung ◽

Kristy Welshhans

Keyword(s):

Down Syndrome ◽

Corpus Callosum ◽

Mouse Model ◽

Hippocampal Neurons ◽

Anterior Commissure ◽

Axon Growth ◽

Chromosome 21 ◽

Ts65dn Mouse ◽

Hippocampal Commissure ◽

Interhemispheric Connectivity

AbstractDown syndrome is the most common genetic cause of intellectual disability and occurs due to the trisomy of human chromosome 21. Adolescent and adult brains from humans with Down syndrome exhibit various neurological phenotypes including a reduction in the size of the corpus callosum, hippocampal commissure and anterior commissure. However, it is unclear when and how these interhemispheric connectivity defects arise. Using the Ts65Dn mouse model of Down syndrome, we examined interhemispheric connectivity in postnatal day 0 (P0) Ts65Dn mouse brains. We find that there is no change in the volume of the corpus callosum or anterior commissure in P0 Ts65Dn mice. However, the volume of the hippocampal commissure is significantly reduced in P0 Ts65Dn mice, and this may contribute to the impaired learning and memory phenotype of this disorder. Interhemispheric connectivity defects that arise during development may be due to disrupted axon growth. In line with this, we find that developing hippocampal neurons display reduced axon length in vitro, as compared to neurons from their euploid littermates. This study is the first to report the presence of defective interhemispheric connectivity at the time of birth in Ts65Dn mice, providing evidence that early therapeutic intervention may be an effective time window for the treatment of Down syndrome.

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Potassium channel regulators are differentially expressed in hippocampi of Ts65Dn and Tc1 Down syndrome mouse models

10.1101/467522 ◽

2018 ◽

Author(s):

Shani Stern ◽

Rinat Keren ◽

Yongsung Kim ◽

Elisha Moses

Keyword(s):

Down Syndrome ◽

Mouse Model ◽

Potassium Channel ◽

Mouse Models ◽

Chromosome 21 ◽

Neuronal Cultures ◽

Rna Expression ◽

Genetic Changes ◽

Expression Levels ◽

Whole Cell Patch Clamp

AbstractBackground:Down syndrome remains the main genetic cause of intellectual disability, with an incidence rate of about 1 in 700 live births. The Ts65Dn mouse strain, with an extra murine chromosome that includes genes from chromosomes 10, 16 and 17 of the mouse and the Tc1 strain with an extra human chromosome 21, are currently accepted as informative and well-studied models for Down Syndrome. Using whole cell patch clamp we recently showed changes in several types of transmembrane currents in hippocampal neuronal cultures of Ts65Dn and Tc1 embryos. The associated genetic changes responsible for these changes in physiology were yet to be studied.Methods:We used qPCR to measure RNA expression level of a few of the channel genes that we suspect are implicated in the previously reported changes of measured currents, and performed statistical analysis using Matlab procedures for the standard t-test and ANOVA and for calculating correlations between the RNA expression levels of several channel genes.Results:We present differential gene expression levels measured using qPCR of the potassium channel regulators KCNE1 and KCNE2 in both Ts65Dn and Tc1 embryos and pups compared to controls. In Tc1, the human genes KCNJ6 and KCNJ15 are expressed in addition to a statistically insignificant increase of expression in the mouse genes KCNJ6 and KCNJ15. All channel genes that we have measured with large replication, have the same up-regulation or down-regulation in both mouse models, indicating that the transcription mechanism acts similarly in these two mouse models. The large dataset furthermore allows us to observe correlations between different channel genes. We find that, despite the significant changes in expression levels, channels that are known to interact have a high and significant correlation in expression both in controls and in the Down syndrome mouse model.Conclusions:We suggest the differential expression of KCNE1 and KCNE2 as a possible cause for our previously reported changes in potassium currents. We report a KCNJ6 and KCNJ15 overexpression, which plays a role in the increased input conductance and the reduced cell excitability that we previously reported in the Tc1 mouse model. The large and significant positive (KCNQ2-KCNQ3, KCNE1-KCNE2, KCNQ3-KCNE1, KCNQ2-KCNE1, KCNQ2-KCNE2, KCNQ3-KCNE2) and negative correlations (KCNE1-KCNJ15, KCNE2-KCNJ15) that we find between channel genes indicate that these genes probably work in a cooperative or in a mutually exclusive manner.

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Highly penetrant myeloproliferative disease in the Ts65Dn mouse model of Down syndrome

Blood ◽

10.1182/blood-2007-04-085670 ◽

2008 ◽

Vol 111 (2) ◽

pp. 767-775 ◽

Cited By ~ 68

Author(s):

Gina Kirsammer ◽

Sarah Jilani ◽

Hui Liu ◽

Elizabeth Davis ◽

Sandeep Gurbuxani ◽

...

Keyword(s):

Down Syndrome ◽

Mouse Model ◽

Gene Dosage ◽

Hematologic Malignancies ◽

Chromosome 21 ◽

Myeloproliferative Disease ◽

Ts65dn Mouse ◽

Hematopoietic Stem ◽

Megakaryoblastic Leukemia ◽

Increased Risk

Children with Down syndrome (DS) display macrocytosis, thrombocytosis, and a 500-fold increased risk of developing megakaryocytic leukemia; however, the specific effects of trisomy 21 on hematopoiesis remain poorly defined. To study this question, we analyzed blood cell development in the Ts65Dn mouse model of DS. Ts65Dn mice are trisomic for 104 orthologs of Hsa21 genes and are the most widely used mouse model for DS. We discovered that Ts65Dn mice display persistent macrocytosis and develop a myeloproliferative disease (MPD) characterized by profound thrombocytosis, megakaryocyte hyperplasia, dysplastic megakaryocyte morphology, and myelofibrosis. In addition, these animals bear distorted hematopoietic stem and myeloid progenitor cell compartments compared with euploid control littermates. Of the 104 trisomic genes in Ts65Dn mice, Aml1/Runx1 attracts considerable attention as a candidate oncogene in DS–acute megakaryoblastic leukemia (DS-AMKL). To determine whether trisomy for Aml1/Runx1 is essential for MPD, we restored disomy at the Aml1/Runx1 locus in the Ts65Dn strain. Surprisingly, trisomy for Aml1/Runx1 is not required for megakaryocyte hyperplasia and myelofibrosis, suggesting that trisomy for one or more of the remaining genes can promote this disease. Our studies demonstrate the potential of DS mouse models to improve our understanding of chromosome 21 gene dosage effects in human hematologic malignancies.

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A mouse model of Down syndrome trisomic for all human chromosome 21 syntenic regions

Human Molecular Genetics ◽

10.1093/hmg/ddq179 ◽

2010 ◽

Vol 19 (14) ◽

pp. 2780-2791 ◽

Cited By ~ 130

Author(s):

Tao Yu ◽

Zhongyou Li ◽

Zhengping Jia ◽

Steven J. Clapcote ◽

Chunhong Liu ◽

...

Keyword(s):

Down Syndrome ◽

Mouse Model ◽

Human Chromosome ◽

Chromosome 21 ◽

Human Chromosome 21 ◽

Syntenic Regions

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Adult-Onset Fluoxetine Treatment Does Not Improve Behavioral Impairments and May Have Adverse Effects on the Ts65Dn Mouse Model of Down Syndrome

Neural Plasticity ◽

10.1155/2012/467251 ◽

2012 ◽

Vol 2012 ◽

pp. 1-10 ◽

Cited By ~ 24

Author(s):

Markus Heinen ◽

Moritz M. Hettich ◽

Devon P. Ryan ◽

Susanne Schnell ◽

Katharina Paesler ◽

...

Keyword(s):

Down Syndrome ◽

Mouse Model ◽

Chromosome 21 ◽

Adult Onset ◽

Ts65dn Mouse ◽

Receptor Antagonists ◽

Memory Impairments ◽

Severe Intellectual Disability ◽

Fluoxetine Treatment ◽

Behavioral Impairments

Down syndrome is caused by triplication of chromosome 21 and is associated with neurocognitive phenotypes ranging from severe intellectual disability to various patterns of more selective neuropsychological deficits, including memory impairments. In the Ts65Dn mouse model of Down syndrome, excessive GABAergic neurotransmission results in local over-inhibition of hippocampal circuits, which dampens hippocampal synaptic plasticity and contributes to cognitive impairments. Treatments with several GABAAreceptor antagonists result in increased plasticity and improved memory deficits in Ts65Dn mice. These GABAAreceptor antagonists are, however, not suitable for clinical applications. The selective serotonin reuptake inhibitor fluoxetine, in contrast, is a widely prescribed antidepressant that can also enhance plasticity in the adult rodent brain by lowering GABAergic inhibition. For these reasons, we wondered if an adult-onset 4-week oral fluoxetine treatment restores spatial learning and memory impairments in Ts65Dn mice. Fluoxetine did not measurably improve behavioral impairments of Ts65Dn mice. On the contrary, we observed seizures and mortality in fluoxetine-treated Ts65Dn mice, raising the possibility of a drug × genotype interaction with respect to these adverse treatment outcomes. Future studies should re-address this in larger animal cohorts and determine if fluoxetine treatment is associated with adverse treatment effects in individuals with Down syndrome.

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A non-mosaic humanized mouse model of Down syndrome, trisomy of a nearly complete long arm of human chromosome 21 in mouse chromosome background

10.1101/862433 ◽

2019 ◽

Cited By ~ 2

Author(s):

Yasuhiro Kazuki ◽

Feng J. Gao ◽

Yicong Li ◽

Anna J. Moyer ◽

Benjamin Devenney ◽

...

Keyword(s):

Down Syndrome ◽

Mouse Model ◽

Human Chromosome ◽

Mouse Models ◽

Artificial Chromosome ◽

Human Condition ◽

Chromosome 21 ◽

Humanized Mouse ◽

Human Chromosome 21 ◽

Functional Features

AbstractDown syndrome (DS) is a complex human condition, and animal models trisomic for human chromosome 21 (HSA21) genes or orthologs provide insights into better understanding and treating DS. However, HSA21 orthologs are distributed into three mouse chromosomes, preventing us from generating mouse models trisomy of a complete set of HSA21 orthologs. The only existing humanized mouse DS model, Tc1, carries a HSA21 with over 20% of protein coding genes (PCGs) disrupted. More importantly, due to the human centromere, Tc1 is mosaic (a mix of euploid and trisomic cells), which makes every mouse unique and compromises interpretation of results. Here, we used mouse artificial chromosome (MAC) technology to “clone” the 34 MB long arm of HSA21 (HSA21q). Through multiple steps of microcell-mediated chromosome transfer we created a new humanized DS mouse model, Tc(HSA21q;MAC)1Yakaz (“TcMAC21”). Constitutive EGFP expression from the transchromosome and fluorescent in situ hybridization validate that TcMAC21, containing a hybrid chromosome of HSA21q and mouse centromere, is not mosaic. Whole genome sequencing shows that TcMAC21 contains a nearly complete copy of HSA21q with 93% of intact PCGs, while RNA-seq and additional mRNA/protein expression analyses confirm that PCGs are transcribed and regulated. A battery of tests show that TcMAC21 recapitulates many DS phenotypes including morphological anomalies in heart, craniofacial skeleton and brain, pathologies at molecular and cellular level, and impairments in learning, memory and synaptic plasticity. TcMAC21 is the most complete mouse model of DS extant and has potential for supporting a wide range of basic and preclinical research.Significance StatementIn the last 25 years, mouse models of trisomy 21 have supported research into Down syndrome, from defining the basis for developmental effects up to support for clinical trials. However, existing models have significant shortfalls, especially for preclinical studies. These deficiencies include incomplete or inappropriate representation of trisomic genes, absence of an extra chromosome, and mosaicism.Using cutting edge technologies we produced a mouse artificial chromosome containing the entire 34Mb long arm of human chromosome 21 and, with assisted reproductive technologies, established it in the germ line of mice. This trisomic mouse manifests developmental and functional features of Down syndrome, including hippocampal-based learning and memory deficits. This is the most complete model of Down syndrome produced to date.

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