Molecular and Cellular Neuroscience (Mol Cell Neurosci)

Publications in this journal

• Article: The Onecut transcription factor HNF-6 contributes to proper reorganization of Purkinje cells during postnatal cerebellum development.

  Emilie Audouard, Olivier Schakman, Audrey Ginion, Luc Bertrand, Philippe Gailly, Frédéric Clotman
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  ABSTRACT: The Onecut (OC) family of transcription factors comprises three members in mammals, namely HNF-6 (or OC-1), OC-2 and OC-3. During embryonic development, these transcriptional activators control cell differentiation in pancreas, in liver and in the nervous system. Adult Hnf6 mutant mice exhibit locomotion defects characterized by hindlimb muscle weakness, abnormal gait and defective balance and coordination. Indeed, HNF-6 is required in spinal motor neurons for proper formation of the hindlimb neuromuscular junctions, which likely explain muscle weakness observed in corresponding mutant animals. The goal of the present study was to determine the cause of the balance and coordination defects in Hnf6 mutant mice. Coordination and balance deficits were quantified by rotarod and runway tests. Hnf6 mutant animals showed an increase in the fall frequency from the beam and were unable to stay on the rotarod even at low speed, indicating a severe balance and coordination deficit. To identify the origin of this abnormality, we assessed whether the development of the main CNS structure involved in the control of balance and coordination, namely the cerebellum, was affected by the absence of HNF-6. Firstly, we observed that Hnf6 was expressed transiently during the first week after birth in the Purkinje cells of wild type newborn mice. Secondly, we showed that, in Hnf6-/- mice, the organization of Purkinje cells became abnormal during a second phase of their development. Indeed, Purkinje cells were produced normally but part of them failed to reorganize as a regular continuous monolayer at the interface between the molecular and the granular layer of the cerebellum. Thus, the Onecut factor HNF-6 contributes to the reorganization of Purkinje cells during a late phase of cerebellar development.
  Molecular and Cellular Neuroscience 05/2013;
• Article: The Chemorepulsive Axon Guidance Protein Semaphorin 3A is a Constituent of Perineuronal Nets in the Adult Rodent Brain.

  Tam Vo, Daniela Carulli, Erich M E Ehlert, Jessica C F Kwok, Gunnar Dick, Vasil Mecollari, Elizabeth B Moloney, Gera Neufeld, Fred de Winter, James W Fawcett, Joost Verhaagen
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  ABSTRACT: In the adult rodent brain, subsets of neurons are surrounded by densely organised extracellular matrix called perineuronal nets (PNNs). PNNs consist of hyaluronan, tenascin-R, chondroitin sulphate proteoglycans (CSPGs), and the link proteins Crtl1 and Bral1. PNNs restrict plasticity at the end of critical periods and can be visualised with Wisteria floribunda agglutinin (WFA). Using a number of antibodies raised against different regions of Semaphorin 3A (Sema3A) we demonstrate that this secreted chemorepulsive axon guidance protein is localised to WFA-positive PNNs around inhibitory interneurons in the cortex and several other PNN-bearing neurons throughout the brain and co-localises with aggrecan, versican, phosphacan and tenascin-R. Chondroitinase ABC (ChABC) was injected in the cortex to degrade glycosaminoglycans (GAGs) from the CSPGs, abolishing WFA staining of PNNs around the injection site. Sema3A-positive nets were no longer observed in the area devoid of WFA staining. In mice lacking the link protein Crtl1 in the CNS only vestigial PNNs are present, and in these mice there were no Sema3A-positive PNN structures. A biochemical analysis shows that Sema3A protein binds with high-affinity to CS-GAGs and aggrecan and versican extracted from PNNs in the adult rat brain, and a significant proportion of Sema3A is retrieved in brain extracts that are enriched in PNN-associated GAGs. The Sema3A receptor components PlexinA1 and A4 are selectively expressed by inhibitory interneurons in the cortex that are surrounded by Sema3A positive PNNs. We conclude that the chemorepulsive axon guidance molecule Sema3A is present in PNNs of the adult rodent brain, bound to the GAGs of the CSPGs. These observations suggest a novel concept namely that chemorepulsive axon guidance molecules like Sema3A may be important functional attributes of PNNs in the adult brain.
  Molecular and Cellular Neuroscience 05/2013;
• Article: Convergence of FPR-rs3-expressing neurons in the mouse accessory olfactory bulb.

  Quentin Dietschi, Alexis Assens, Ludivine Challet, Alan Carleton, Ivan Rodriguez
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  ABSTRACT: In the mouse, most members of the FPR receptor family are expressed by vomeronasal sensory neurons. The neural circuitry corresponding to this class of chemical sensors is unknown. Taking advantage of the presence of FPR-rs3 on both vomeronasal dendrites and axonal fibers, we visualized the distribution of sensory cells expressing this member of the FPR family, and their corresponding axonal projections in the olfactory bulb. We found a rostrocaudal gradient of receptor choice frequency in the vomeronasal sensory neuroepithelium, and observed a convergence of FPR-rs3 axons into multiple, linked and deeply located glomeruli. These were homogenously innervated, and spatially restricted to the basal portion of the rostral accessory olfactory bulb. This organization, reminiscent of the one that characterizes axonal projections of V1R-expressing neurons, supports a role played by these receptors in the perception of semiochemicals.
  Molecular and Cellular Neuroscience 05/2013;
• Article: Differential role of Dok1 and Dok2 in TLR2-induced inflammatory signaling in glia.

  Eric J Downer, Daniel Johnston, Marina A Lynch
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  ABSTRACT: Accumulating evidence continues to underpin the role of the innate immune system in pathologies associated with neuroinflammation. Innate immunity is regulated by pattern recognition receptors that detect pathogens and, in the case of Gram-positive bacteria, binding of bacterial lipopeptides to toll-like receptor (TLR)2 is emerging as an important mechanism controlling glial cell activation. In the present study, we employed the use of the synthetic bacterial lipoprotein and a selective TLR2 agonist, Pam3CSK4, to induce inflammatory signaling in microglia and astrocytes. The adaptor proteins, downstream of kinase (Dok)1 and Dok2, are known to have a role in negatively regulating the Ras-ERK signaling cascade, with downstream consequences on pro-inflammatory cytokine expression. Data presented herein demonstrate that TLR2 enhanced the tyrosine phosphorylation of Dok1 and Dok2 in astrocytes and microglia, and that knockdown of these adaptors using small interfering RNA robustly elevated TLR2-induced ERK activation. Importantly, TLR2-induced NF-κB activation and IL-6 production was exacerbated in astrocytes transfected with Dok1 and Dok2 siRNA, indicating that both Dok proteins negatively regulate TLR2-induced inflammatory signaling in astrocytes. In contrast, Dok1 knockdown attenuated TLR2-induced NF-κB activation and IL-6 production in microglia, while Dok2 siRNA failed to affect TLR2-induced NF-κB activity and subsequent cytokine expression in this cell type. Overall this indicates that Dok1 and Dok2 are novel adaptors for TLR2 in glial cells and, importantly, indicates that Dok1 and Dok2 differentially regulate TLR2-induced pro-inflammatory signaling in astrocytes and microglia.
  Molecular and Cellular Neuroscience 05/2013;
• Article: Neurotrophin and Wnt signaling cooperatively regulate dendritic spine formation.

  Brian G Hiester, Domenico F Galati, Patricia C Salinas, Kevin R Jones
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  ABSTRACT: Dendritic spines are major sites of excitatory synaptic transmission and changes in their numbers and morphology have been associated with neurodevelopmental and neurodegenerative disorders. Brain-derived Neurotrophic Factor (BDNF) is a secreted growth factor that influences hippocampal, striatal and neocortical pyramidal neuron dendritic spine density. However, the mechanisms by which BDNF regulates dendritic spines, and how BDNF interacts with other regulators of spines remain unclear. We propose that one mechanism by which BDNF promotes dendritic spine formation is through an interaction with Wnt signaling. Here, we show that Wnt signaling inhibition in cultured cortical neurons disrupts dendritic spine development, reduces dendritic arbor size and complexity, and blocks BDNF-induced dendritic spine formation and maturation. Additionally, we show that BDNF regulates expression of Wnt2, and that Wnt2 is sufficient to promote cortical dendrite growth and dendritic spine formation. Together, these data suggest that BDNF and Wnt signaling cooperatively regulate dendritic spine formation.
  Molecular and Cellular Neuroscience 04/2013;
• Article: Splicing therapy for neuromuscular disease.

  Andrew G L Douglas, Matthew J A Wood
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  ABSTRACT: Duchenne muscular dystrophy (DMD) and spinal muscular atrophy (SMA) are two of the most common inherited neuromuscular diseases in humans. Both conditions are fatal and no clinically available treatments are able to significantly alter disease course in either case. However, by manipulation of pre-mRNA splicing using antisense oligonucleotides, defective transcripts from the DMD gene and from the SMN2 gene in SMA can be modified to once again produce protein and restore function. A large number of in vitro and in vivo studies have validated the applicability of this approach and an increasing number of preliminary clinical trials have either been completed or are under way. Several different oligonucleotide chemistries can be used for this purpose and various strategies are being developed to facilitate increased delivery efficiency and prolonged therapeutic effect. As these novel therapeutic compounds start to enter the clinical arena, attention must also be drawn to the question of how best to facilitate the clinical development of such personalised genetic therapies and how best to implement their provision.
  Molecular and Cellular Neuroscience 04/2013;
• Article: Predicting Protein-Protein Interactions in the Post Synaptic Density.

  Ossnat Bar-Shira, Gal Chechik
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  ABSTRACT: The post synaptic density (PSD) is a specialization of the cytoskeleton at the synaptic junction, composed of hundreds of different proteins. Characterizing the protein components of the PSD and their interactions can help elucidate the mechanism of long-term changes in synaptic plasticity, which underlie learning and memory. Unfortunately, our knowledge of the proteome and interactome of the PSD is still partial and noisy. In this study we describe a computational framework to improve the reconstruction of the PSD network. The approach is based on learning the characteristics of PSD protein interactions from a set of trusted interactions, expanding this set with data collected from large scale repositories, and then predicting novel interaction with proteins that are suspected to reside in the PSD. Using this method we obtained thirty predicted interactions, with more than half of which having supporting evidence in the literature. We discuss in details two of these new interactions, Lrrtm1 with PSD-95 and Src with Capg. The first may take part in a mechanism underlying glutamatergic dysfunction in schizophrenia. The second suggests an alternative mechanism to regulate dendritic spines maturation.
  Molecular and Cellular Neuroscience 04/2013;
• Article: The role of chromogranin B in an animal model of multiple sclerosis.

  Michelle Mo, Ha Thi Hoang, Stefan Schmidt, Robert B Clark, Barbara E Ehrlich
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  ABSTRACT: Chromogranin B (CGB) is a high capacity, low affinity calcium binding protein in the endoplasmic reticulum (ER) that binds to the inositol 1,4,5 trisphosphate receptor (InsP3R) and amplifies calcium release from ER stores. Recently, it was discovered that levels of CGB-derived peptides are decreased in the cerebrospinal fluid of multiple sclerosis (MS) patients. One of the mechanisms by which neurodegeneration in MS is thought to occur is through increased levels of intra-axonal calcium. The combination of excess intracellular calcium and dysregulated levels of CGB in MS led us to hypothesize that CGB may be involved in MS pathophysiology. Here, we show in a mouse model of MS that CGB levels are elevated in neurons prior to onset of symptoms. Once symptoms develop, CGB protein levels increase with disease severity. Additionally, we show that elevated levels of CGB may have a role in the pathophysiology of MS and suggest that the initial elevation of CGB, prior to symptom onset, is due to inflammatory processes. Upon development of symptoms, CGB accumulation in neurons results from decreased ubiquitination and decreased secretion. Furthermore, we show that calpain activity is increased and levels of InsP3R are decreased. From these results, we suggest that the elevated levels of CGB and altered InsP3R levels may contribute to the axonal/neuronal damage and dysregulated calcium homeostasis observed in MS. Additionally, we propose that CGB can be a biomarker that predicts the onset and severity of disease in patients with MS.
  Molecular and Cellular Neuroscience 04/2013;
• Article: Neuronal myosin-X is upregulated after peripheral nerve injury and mediates laminin-induced growth of neurites.

  Stefan Plantman, Johan Zelano, Liudmila Novikova, Lev Novikov, Staffan Cullheim
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  ABSTRACT: The successful outcome of peripheral neuronal regeneration is attributed both to the growth permissive milieu and the intrinsic ability of the neuron to initiate appropriate cellular responses such as changes in gene expression and cytoskeletal rearrangements. Even though numerous studies have shown the importance of interactions between the neuron and the extracellular matrix (ECM) in axonal outgrowth, the molecular mechanisms underlying the contact between ECM receptors and the cellular cytoskeleton remain largely unknown. Unconventional myosins constitute an important group of cytoskeletal-associated motor proteins. One member of this family is the recently described myosin-X. This protein interacts with several members of the axon growth-associated ECM receptor family of integrins and could therefore be important in neuronal outgrowth. In this study, using radioactive in situ hybridization, we found that expression of myosin-X mRNA is upregulated in adult rat sensory neurons and spinal motoneurons after peripheral nerve injury, but not after central injury. Thus, myosin-X was upregulated after injuries that can be followed by axonal regeneration. We also found that the protein is localized to neuronal growth cones and that silencing of myosin-X using RNA interference impairs the integrin-mediated growth of neurites on laminin, but has no effect on non-integrin mediated growth on N-cadherin.
  Molecular and Cellular Neuroscience 04/2013;
• Article: CLIPing the brain: Studies of protein-RNA interactions important for neurodegenerative disorders.

  Miha Modic, Jernej Ule, Christopher R Sibley
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  ABSTRACT: The fate of an mRNA is largely determined by its interactions with RNA binding proteins (RBPs). Post-transcriptional processing, RNA stability, localisation and translation are some of the events regulated by the plethora of RBPs present within cells. Mutations in various RBPs cause several diseases of the central nervous system, including frontotemporal lobar degeneration, amyotrophic lateral sclerosis and fragile X syndrome. Here we review the studies that integrated UV-induced cross-linked immunoprecipitation (CLIP) with other genome-wide methods to comprehensively characterise the function of diverse RBPs in the brain. We discuss the technical challenges of these studies, and review the strategies that can be used to reliably identify the RNAs bound and regulated by an RBP. We conclude by highlighting how CLIP and related techniques have been instrumental in addressing the role of RBPs in neurologic diseases.
  Molecular and Cellular Neuroscience 04/2013;
• Article: Fused in Sarcoma (FUS): An Oncogene Goes Awry in Neurodegeneration.

  Dorothee Dormann, Christian Haass
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  ABSTRACT: Fused in sarcoma (FUS) is a nuclear DNA/RNA binding protein that regulates different steps of gene expression, including transcription, splicing and mRNA transport. FUS has been implicated in neurodegeneration, since mutations in FUS cause familial amyotrophic lateral sclerosis (ALS-FUS) and lead to the cytosolic deposition of FUS in the brain and spinal cord of ALS-FUS patients. Moreover, FUS and two related proteins of the same protein family (FET family) are co-deposited in cytoplasmic inclusions in a subset of patients with frontotemporal lobar degeneration (FTLD-FUS). Cytosolic deposition of these otherwise nuclear proteins most likely causes the loss of a yet unknown essential nuclear function and/or the gain of a toxic function in the cytosol. Here we summarize what is known about the physiological functions of the FET proteins in the nucleus and cytoplasm and review the distinctive pathomechanisms that lead to the deposition of only FUS in ALS-FUS, but all three FET proteins in FTLD-FUS. We suggest that ALS-FUS is caused by a selective dysfunction of FUS, while FTLD-FUS may be caused by a dysfunction of the entire FET family.
  Molecular and Cellular Neuroscience 04/2013;
• Article: Intramolecular regulation of presynaptic scaffold protein SYD-2/Liprin-α

  Poh Hui Chia, Maulik Patel, Oliver I Wagner, Dieter R Klopfenstein, Kang Shen
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  ABSTRACT: SYD-2/Liprin-α is a multi-domain protein that associates with and recruits multiple active zone molecules to form presynaptic specializations. Given SYD-2's critical role in synapse formation, its synaptogenic ability is likely tightly regulated. However, mechanisms that regulate SYD-2 function are poorly understood. In this study, we provide evidence that SYD-2's function may be regulated by interactions between its coiled-coil (CC) domains and sterile α-motif (SAM) domains. We show that the N-terminal CC domains are necessary and sufficient to assemble functional synapses while C-terminal SAM domains are not, suggesting that the CC domains are responsible for the synaptogenic activity of SYD-2. Surprisingly, syd-2 alleles with single amino acid mutations in the SAM domain show strong loss of function phenotypes, suggesting that SAM domains also play an important role in SYD-2's function. A previously characterized syd-2 gain-of-function mutation within the CC domains is epistatic to the loss-of-function mutations in the SAM domain. In addition, yeast two-hybrid analysis showed interactions between the CC and SAM domains. Thus, the data is consistent with a model where the SAM domains regulate the CC domain-dependent synaptogenic activity of SYD-2. Taken together, our study provides new mechanistic insights into how SYD-2's activity may be modulated to regulate synapse formation during development.
  Molecular and Cellular Neuroscience 03/2013;
• Article: Atorvastatin-modified dendritic cells in vitro ameliorate experimental autoimmune myasthenia gravis by up-regulated Treg cells and shifted Th1/Th17 to Th2 cytokines.

  Xiao-Li Li, Ying Liu, Li-Li Cao, Heng Li, Long-Tao Yue, Shan Wang, Min Zhang, Xiu-Hua Li, Ying-Chun Dou, Rui-Sheng Duan
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  ABSTRACT: Conventional therapies for autoimmune diseases produce nonspecific immune suppression, which are usually continued lifelong to maintain disease control, and associated with a variety of adverse effects. In this study, we found that spleen-derived dendritic cells (DCs) from the ongoing experimental autoimmune myasthenia gravis (EAMG) rats can be induced into tolerogenic DCs by atorvastatin in vitro. Administration of these tolerogenic DCs to EAMG rats on days 5 and 13 post immunization (p.i.) resulted in improved clinical symptoms, which were associated with increased numbers of CD4(+)CD25(+) T regulatory (Treg) cells and Foxp3 expression, decreased lymphocyte proliferation among lymph node mononuclear cells (MNC), shifted cytokine profile from Th1/Th17 to Th2 type cytokines, decreased level of anti-R97-116 peptide (region 97-116 of the rat acetylcholine receptor α subunit) IgG antibody in serum. These tolerogenic DCs can migrate to spleen, thymus, popliteal and inguinal lymph nodes after they were injected into the EAMG rats intraperitoneally. Furthermore, these tolerogenic DCs played their immunomodulatory effects in vivo mainly by decreased expression of CD86 and MHC class II on endogenous DCs. All these data provided us a new strategy to treat EAMG and even human myasthenia gravis (MG).
  Molecular and Cellular Neuroscience 03/2013;
• Article: Postsynaptic FMRP bi-directionally regulates excitatory synapses as a function of developmental age and MEF2 activity.

  Tong Zang, Marina A Maksimova, Christopher W Cowan, Rhonda Bassel-Duby, Eric N Olson, Kimberly M Huber
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  ABSTRACT: Rates of synapse formation and elimination change over the course of postnatal development, but little is known of molecular mechanisms that mediate this developmental switch. Here we report that the dendritic RNA binding protein Fragile X Mental Retardation Protein (FMRP) bi-directionally and cell autonomously regulates excitatory synaptic function which depends on developmental age as well as function of the activity-dependent transcription factor Myocyte-Enhancer Factor 2 (MEF2). Acute postsynaptic expression of FMRP in CA1 neurons of hippocampal slice cultures (during the first postnatal week; P6-7) promotes synapse function and maturation. In contrast, acute expression of FMRP or endogenous FMRP in more mature neurons (during the second postnatal week; P13-16) suppresses synapse number. The ability of neuronal depolarization to stimulate MEF2 transcriptional activity increases over this same developmental time period. Knockout of endogenous MEF2 isoforms causes acute postsynaptic FMRP expression to promote, instead of eliminate, synapses onto two week old neurons. Conversely, expression of active MEF2 in neonatal neurons results in a precocious FMRP-dependent synapse elimination. Our findings suggest that FMRP and MEF2 function together to fine tune synapse formation and elimination rates in response to neuronal activity levels over the course of postnatal development.
  Molecular and Cellular Neuroscience 03/2013;
• Article: Insulin-like growth factor 1 inhibits hair-cell apoptosis and promotes the cell cycle of supporting cells by activating different downstream cascades after pharmacological hair cell injury in neonatal mice.

  Yushi Hayashi, Norio Yamamoto, Takayuki Nakagawa, Juichi Ito
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  ABSTRACT: Sensorineural hearing loss, which is mainly caused by cochlear hair cell damage, is an intractable disease, as cochlear hair cells and supporting cells are unable to proliferate in postnatal mammals. As a novel and potent treatment for sensorineural hearing loss, we have studied IGF-1 and found that it protects cochlear hair cells from the damage caused by noise and ischemic trauma. Through a clinical trial, we have also confirmed that IGF-1 is an effective treatment for idiopathic sudden sensorineural hearing loss. In the current study, we attempted to identify the downstream pathways of the IGF-1 signal and the mechanisms by which IGF-1 protects the neonatal mouse cochlear hair cells that have been damaged by neomycin. IGF-1 activated both the PI3K/Akt and MEK/ERK pathways to maintain the hair cell numbers in the injured cochlea. The PI3K/Akt pathway specifically protected the cochlear inner hair cells through the inhibition of apoptosis. In contrast, the MEK/ERK pathway induced the cell cycle promotion of Hensen's and Claudius' cells, the supporting cells that are located lateral to the outer hair cells of the cochlea. This cell cycle promotion of the supporting cells resulted in the maintenance of the outer hair cell numbers. These results indicate that IGF-1 is a growth factor that efficiently regulates different mechanisms through different downstream cascades, thereby protecting cochlear hair cells.
  Molecular and Cellular Neuroscience 03/2013;
• Article: 7,8-Dihydroxyflavone leads to survival of cultured embryonic motoneurons by activating intracellular signaling pathways.

  Tsai T, Klausmeyer A, Conrad R, Gottschling C, Leo M, Faissner A, Wiese S
  Molecular and Cellular Neuroscience 03/2013;
• Article: 7,8-dihydroxyflavone leads to survival of cultured embryonic motoneurons by activating intracellular signaling pathways.

  Teresa Tsai, Alice Klausmeyer, Rebecca Conrad, Christine Gottschling, Markus Leo, Andreas Faissner, Stefan Wiese
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  ABSTRACT: Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family and a ligand for the tropomyosin-receptor kinase B (TrkB), mediates neuronal survival, differentiation, and synaptic plasticity. However, BDNF is not used to treat neurodegenerative diseases because of its poor pharmacokinetic profile, side effects, and absence of survival properties in clinical trials. Consequently, alternative approaches such as TrkB receptor agonist application are gaining importance. 7,8-dihydroxyflavone (7,8-DHF), a member of the flavonoid family, has been described as a robust TrkB receptor agonist in hippocampal neurons. Nevertheless, the influence of 7,8-DHF on motoneurons, one of the main targets of BDNF in vivo, are so far unknown. Therefore, we investigated the impact of 7,8-DHF treatment on primary cultured mouse motoneurons. Indeed, we found an activation of the TrkB receptor. Moreover, 7,8-DHF application promotes survival and neurite growth of cultured motoneurons and these effects appear dose-dependent. To investigate the PI3K/AKT and MAPK pathway activation in 7,8-DHF treated motoneurons, we developed a high-density culture system of primary mouse motoneurons. Analysis of both pathways demonstrated a PI3K/AKT but not MAPK pathway activation in cultured motoneurons. This is in contrast to previously published reports about BDNF-mediated activation of TrkB. The lack of MAPK pathway activation is also in contrast to what has been found for hippocampal neurons that indeed show MAPK activation after 7,8-DHF treatment. The ability of 7,8-DHF to imitate BDNF function in motoneurons by using Trk receptor signaling would provide a new approach for treatment of motoneuron diseases, but needs a more detailed analysis of the activation profile of 7,8-DHF.
  Molecular and Cellular Neuroscience 03/2013;
• Article: Modeling Huntington's Disease with Induced Pluripotent Stem Cells.

  Julia A Kaye, Steven Finkbeiner
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  ABSTRACT: Huntington's disease (HD) causes severe motor dysfunction, behavioral abnormalities, cognitive impairment and death. Investigations into its molecular pathology have primarily relied on murine tissues; however, the recent discovery of induced pluripotent stem cells (iPSCs) has opened new possibilities to model neurodegenerative disease using cells derived directly from patients, and therefore may provide a human-cell-based platform for unique insights into the pathogenesis of HD. Here, we will examine the practical implementation of iPSCs to study HD, such as approaches to differentiate embryonic stem cells (ESCs) or iPSCs into medium spiny neurons, the cell type most susceptible in HD. We will explore the HD-related phenotypes identified in iPSCs and ESCs and review how brain development and neurogenesis may actually be altered early, before the onset of HD symptoms, which could inform the search for drugs that delay disease onset. Finally, we will speculate on the exciting possibility that ESCs or iPSCs might be used as therapeutics to restore or replace dying neurons in HD brains.
  Molecular and Cellular Neuroscience 02/2013;
• Article: Heterochronic misexpression of Ascl1 in the Atoh7 retinal cell lineage blocks cell cycle exit.

  Robert B Hufnagel, Amy N Riesenberg, Malgorzata Quinn, Joseph A Brzezinski, Tom Glaser, Nadean L Brown
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  ABSTRACT: Retinal neurons and glia arise from a common progenitor pool in a temporal order, with retinal ganglion cells (RGCs) appearing first, and Müller glia last. The transcription factors Atoh7/Math5 and Ascl1/Mash1 represent divergent bHLH clades, and exhibit distinct spatial and temporal retinal expression patterns, with little overlap during early development. Here, we tested the ability of Ascl1 to change the fate of cells in the Atoh7 lineage when misexpressed from the Atoh7 locus, using an Ascl1-IRES-DsRed2 knock-in allele. In Atoh7Ascl1KI/+ and Atoh7Ascl1KI/Ascl1KI embryos, ectopic Ascl1 delayed cell cycle exit and differentiation, even in cells coexpressing Atoh7. The heterozygous retinas recovered, and eventually produced a normal complement of RGCs, while homozygous substitution of Ascl1 for Atoh7 did not promote postnatal retinal fates precociously, nor rescue Atoh7 mutant phenotypes. However, our analyses revealed two unexpected findings. First, ectopic Ascl1 disrupted cell cycle progression within the marked Atoh7 lineage, but also nonautonomously in other retinal cells. Second, the size of the Atoh7 retinal lineage was unaffected, supporting the idea of a compensatory shift of the non-proliferative cohort to maintain lineage size. Overall, we conclude that Ascl1 acts dominantly to block cell cycle exit, but is incapable of redirecting the fates of early RPCs.
  Molecular and Cellular Neuroscience 02/2013;