Publications by authors named "Seong-Seng Tan"

73 Publications

Transcriptome analysis of ankylosed primary molars with infraocclusion.

Int J Oral Sci 2020 02 21;12(1). Epub 2020 Feb 21.

Florey Institute of Neuroscience, The University of Melbourne, Melbourne, Australia.

Primary molar ankylosis with infraocclusion can retard dental arch development and cause dental asymmetry. Despite its widespread prevalence, little is known about its molecular etiology and pathogenesis. To address this, RNA sequencing was used to generate transcriptomes of furcal bone from infraoccluded (n = 7) and non-infraoccluded (n = 9) primary second molars, all without succeeding biscuspids. Of the 18 529 expressed genes, 432 (2.3%) genes were differentially expressed between the two groups (false discovery rate < 0.05). Hierarchical clustering and principal component analysis showed clear separation in gene expression between infraoccluded and non-infraoccluded samples. Pathway analyses indicated that molar ankylosis is associated with the expression of genes consistent with the cellular inflammatory response and epithelial cell turnover. Independent validation using six expressed genes by immunohistochemical analysis demonstrated that the corresponding proteins are strongly expressed in the developing molar tooth germ, in particular the dental follicle and inner enamel epithelium. The descendants of these structures include the periodontal ligament, cementum, bone and epithelial rests of Malassez; tissues that are central to the ankylotic process. We therefore propose that ankylosis involves an increased inflammatory response associated with disruptions to the developmental remnants of the dental follicle and epithelial rests of Malassez.
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http://dx.doi.org/10.1038/s41368-019-0070-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7033215PMC
February 2020

The Ubiquitin Ligase Adaptor NDFIP1 Selectively Enforces a CD8 T Cell Tolerance Checkpoint to High-Dose Antigen.

Cell Rep 2018 07;24(3):577-584

John Curtin School of Medical Research, Australian National University, Canberra, ACT, Australia; Sir Peter MacCallum Department of Oncology, The University of Melbourne, Parkville, VIC, Australia; Cancer Immunology Program, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia. Electronic address:

Escape from peripheral tolerance checkpoints that control cytotoxic CD8 T cells is important for cancer immunotherapy and autoimmunity, but pathways enforcing these checkpoints are mostly uncharted. We reveal that the HECT-type ubiquitin ligase activator, NDFIP1, enforces a cell-intrinsic CD8 T cell checkpoint that desensitizes TCR signaling during in vivo exposure to high antigen levels. Ndfip1-deficient OT-I CD8 T cells responding to high exogenous tolerogenic antigen doses that normally induce anergy aberrantly expanded and differentiated into effector cells that could precipitate autoimmune diabetes in RIP-OVA mice. In contrast, NDFIP1 was dispensable for peripheral deletion to low-dose exogenous or pancreatic islet-derived antigen and had little impact upon effector responses to Listeria or acute LCMV infection. These data provide evidence that NDFIP1 mediates a CD8 T cell tolerance checkpoint, with a different mechanism to CD4 T cells, and indicates that CD8 T cell deletion and anergy are molecularly separable checkpoints.
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http://dx.doi.org/10.1016/j.celrep.2018.06.060DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6112980PMC
July 2018

A method for isolating cortical interneurons sharing the same birthdays for gene expression studies.

Exp Neurol 2017 09 13;295:36-45. Epub 2017 May 13.

Florey Institute of Neuroscience and Mental Health, Parkville, VIC, Australia; University of Melbourne, Parkville, VIC, Australia. Electronic address:

The two neuronal populations in the cortex, pyramidal neurons and interneurons, can be separated based on neurotransmitter identity, however, within this segregation a large degree of diversity exists. Investigations into the molecular diversity of neurons are impeded by the inability to isolate cell populations born at different times for gene expression analysis. Developing interneurons may be distinguished by the expression of Glutamic Acid Decarboxylase-67 (GAD67). Neuronal birthdating using nucleoside analogs is an effective means of identifying coetaneous interneurons. Using these two features, neurotransmitter identity and birthdating, we have developed a method to isolate migrating interneurons using fluorescent-activated cell sorting (FACS) for RNA extraction and gene expression analysis. We utilized 5-ethynyl-2'-deoxyuridine (EdU) to birthdate interneuron cohorts and the GAD67 knock-in GFP transgenic mice to identify interneurons. In combination, we achieved simultaneous detection of GFP and EdU signals during FACS sorting of coetaneous interneurons with minimum loss of RNA integrity. RNA quality was deemed to be satisfactory by quantitative polymerase chain reaction (qPCR) for the interneuron-specific transcript Gad67.
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http://dx.doi.org/10.1016/j.expneurol.2017.05.006DOI Listing
September 2017

Engineered Exosomes as Vehicles for Biologically Active Proteins.

Mol Ther 2017 06 13;25(6):1269-1278. Epub 2017 Apr 13.

The Florey Institute of Neuroscience and Mental Health, The University of Melbourne, Parkville, Victoria 3052, Australia. Electronic address:

Exosomes represent an attractive vehicle for the delivery of biomolecules. However, mechanisms for loading functional molecules into exosomes are relatively unexplored. Here we report the use of the evolutionarily conserved late-domain (L-domain) pathway as a mechanism for loading exogenous proteins into exosomes. We demonstrate that labeling of a target protein, Cre recombinase, with a WW tag leads to recognition by the L-domain-containing protein Ndfip1, resulting in ubiquitination and loading into exosomes. Our results show that Ndfip1 expression acts as a molecular switch for exosomal packaging of WW-Cre that can be suppressed using the exosome inhibitor GW4869. When taken up by floxed reporter cells, exosomes containing WW-Cre were capable of inducing DNA recombination, indicating functional delivery of the protein to recipient cells. Engineered exosomes were administered to the brain of transgenic reporter mice using the nasal route to test for intracellular protein delivery in vivo. This resulted in the transport of engineered exosomes predominantly to recipient neurons in a number of brain regions, including the olfactory bulb, cortex, striatum, hippocampus, and cerebellum. The ability to engineer exosomes to deliver biologically active proteins across the blood-brain barrier represents an important step for the development of therapeutics to treat brain diseases.
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http://dx.doi.org/10.1016/j.ymthe.2017.03.030DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5474961PMC
June 2017

The HSA21 gene EURL/C21ORF91 controls neurogenesis within the cerebral cortex and is implicated in the pathogenesis of Down Syndrome.

Sci Rep 2016 07 11;6:29514. Epub 2016 Jul 11.

EMBL Australia, The Australian Regenerative Medicine Institute, Monash University, Clayton, Victoria 3800, Australia.

Copy number variations to chromosome 21 (HSA21) cause intellectual disability and Down Syndrome, but our understanding of the HSA21 genetic factors which contribute to fetal brain development remains incomplete. Here, we focussed on the neurodevelopmental functions for EURL (also known as C21ORF91, Refseq Gene ID:54149), a protein-coding gene at the centromeric boundary of the Down Syndrome Critical Region (DSCR) of HSA21. We report that EURL is expressed during human and mouse cerebral cortex development, and we report that alterations to EURL mRNA levels within the human brain underlie Down Syndrome. Our gene perturbation studies in mice demonstrate that disruptions to Eurl impair progenitor proliferation and neuronal differentiation. Also, we find that disruptions to Eurl impair the long-term positioning and dendritic spine densities of cortical projection neurons. We provide evidence that EURL interacts with the coiled-coil domain-containing protein CCDC85B so as to modulate β-catenin levels in cells. Further, we utilised a fluorescent reporter (8xTOPFLASHd2EGFP) to demonstrate that disruptions to Eurl alter β-catenin signalling in vitro as well as in vivo. Together, these studies highlight EURL as an important new player in neuronal development that is likely to impact on the neuropathogenesis of HSA21-related disorders including Down Syndrome.
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http://dx.doi.org/10.1038/srep29514DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4941730PMC
July 2016

An aesthetic approach towards the temporary restoration of missing upper lateral incisors during orthodontic treatment.

Aust Orthod J 2015 Nov;31(2):236-8

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November 2015

Cortical Layer Inversion and Deregulation of Reelin Signaling in the Absence of SOCS6 and SOCS7.

Cereb Cortex 2017 01;27(1):576-588

Walter and Eliza Hall Institute of Medical Research, Melbourne, Parkville, VIC 3052, Australia.

Mutations of the reelin gene cause severe defects in cerebral cortex development and profound intellectual impairment. While many aspects of the reelin signaling pathway have been identified, the molecular and ultimate cellular consequences of reelin signaling remain unknown. Specifically, it is unclear if termination of reelin signaling is as important for normal cortical neuron migration as activation of reelin signaling. Using mice that are single or double deficient, we discovered that combined loss of the suppressors of cytokine signaling, SOCS6 and SOCS7, recapitulated the cortical layer inversion seen in mice lacking reelin and led to a dramatic increase in the reelin signaling molecule disabled (DAB1) in the cortex. The SRC homology domains of SOCS6 and SOCS7 bound DAB1 ex vivo. Mutation of DAB1 greatly diminished binding and protected from degradation by SOCS6. Phosphorylated DAB1 was elevated in cortical neurons in the absence of SOCS6 and SOCS7. Thus, constitutive activation of reelin signaling was observed to be equally detrimental as lack of activation. We hypothesize that, by terminating reelin signaling, SOCS6 and SOCS7 may allow new cycles of reelin signaling to occur and that these may be essential for cortical neuron migration.
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http://dx.doi.org/10.1093/cercor/bhv253DOI Listing
January 2017

Ndfip1 represses cell proliferation by controlling Pten localization and signaling specificity.

J Mol Cell Biol 2015 Apr 23;7(2):119-31. Epub 2015 Mar 23.

Brain Development and Regeneration Division, Florey Institute of Neuroscience and Mental Health, The University of Melbourne, Parkville, Victoria 3010, Australia

Pten controls a signaling axis that is implicated to regulate cell proliferation, growth, survival, migration, and metabolism. The molecular mechanisms underlying the specificity of Pten responses to such diverse cellular functions are currently poorly understood. Here we report the control of Pten activity and signaling specificity during the cell cycle by Ndfip1 regulation of Pten spatial distribution. Genetic deletion of Ndfip1 resulted in a loss of Pten nuclear compartmentalization and increased cell proliferation, despite cytoplasmic Pten remaining active in regulating PI3K/Akt signaling. Cells lacking nuclear Pten were found to have dysregulated levels of Plk1 and cyclin D1 that could drive cell proliferation. In vivo, transgene expression of Ndfip1 in the developing brain increased nuclear Pten and lengthened the cell cycle of neuronal progenitors, resulting in microencephaly. Our results show that local partitioning of Pten from the cytoplasm to the nucleus represents a key mechanism contributing to the specificity of Pten signaling during cell proliferation.
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http://dx.doi.org/10.1093/jmcb/mjv020DOI Listing
April 2015

Nedd4 family interacting protein 1 (Ndfip1) is required for ubiquitination and nuclear trafficking of BRCA1-associated ATM activator 1 (BRAT1) during the DNA damage response.

J Biol Chem 2015 Mar 28;290(11):7141-50. Epub 2015 Jan 28.

From the Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, 3010 Victoria, Australia,

During injury, cells are vulnerable to apoptosis from a variety of stress conditions including DNA damage causing double-stranded breaks. Without repair, these breaks lead to aberrations in DNA replication and transcription, leading to apoptosis. A major response to DNA damage is provided by the protein kinase ATM (ataxia telangiectasia mutated) that is capable of commanding a plethora of signaling networks for DNA repair, cell cycle arrest, and even apoptosis. A key element in the DNA damage response is the mobilization of activating proteins into the cell nucleus to repair damaged DNA. BRAT1 is one of these proteins, and it functions as an activator of ATM by maintaining its phosphorylated status while also keeping other phosphatases at bay. However, it is unknown how BRAT1 is trafficked into the cell nucleus to maintain ATM phosphorylation. Here we demonstrate that Ndfip1-mediated ubiquitination of BRAT1 leads to BRAT1 trafficking into the cell nucleus. Without Ndfip1, BRAT1 failed to translocate to the nucleus. Under genotoxic stress, cells showed increased expression of both Ndfip1 and phosphorylated ATM. Following brain injury, neurons show increased expression of Ndfip1 and nuclear translocation of BRAT1. These results point to Ndfip1 as a sensor protein during cell injury and Ndfip1 up-regulation as a cue for BRAT1 ubiquitination by Nedd4 E3 ligases, followed by nuclear translocation of BRAT1.
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http://dx.doi.org/10.1074/jbc.M114.613687DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4358134PMC
March 2015

PTEN secretion in exosomes.

Methods 2015 May 24;77-78:157-63. Epub 2014 Dec 24.

Brain Development and Regeneration Laboratory, The Florey Institute of Neuroscience and Mental Health, The University of Melbourne, Parkville, Australia. Electronic address:

PTEN was discovered as a membrane-associated tumor suppressor protein nearly two decades ago, but the concept that it can be secreted and taken up by recipient cells is revolutionary. Since then, various laboratories have reported that PTEN is indeed secreted and available for uptake by other cells in at least two different guises. First, PTEN may be packaged and exported within extracellular vesicles (EV) called exosomes. Second, PTEN may also be secreted as a naked protein in a longer isoform called PTEN-long. While the conditions favouring the secretion of PTEN-long remain unknown, PTEN secretion in exosomes is enhanced by the Ndfip1/Nedd4 ubiquitination system. In this report, we describe conditions for packaging PTEN in exosomes and their potential use for mediating non cell-autonomous functions in recipient cells. We suggest that this mode of PTEN transfer may potentially provide beneficial PTEN for tumor suppression, however it may also propagate deleterious versions of mutated PTEN causing tumorigenesis.
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http://dx.doi.org/10.1016/j.ymeth.2014.12.016DOI Listing
May 2015

A unified nomenclature and amino acid numbering for human PTEN.

Sci Signal 2014 Jul 1;7(332):pe15. Epub 2014 Jul 1.

Institute of Biological Chemistry, Biophysics and Bioengineering, School of Engineering and Physical Sciences, Heriot Watt University, Edinburgh, UK.

The tumor suppressor PTEN is a major brake for cell transformation, mainly due to its phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P3] phosphatase activity that directly counteracts the oncogenicity of phosphoinositide 3-kinase (PI3K). PTEN mutations are frequent in tumors and in the germ line of patients with tumor predisposition or with neurological or cognitive disorders, which makes the PTEN gene and protein a major focus of interest in current biomedical research. After almost two decades of intense investigation on the 403-residue-long PTEN protein, a previously uncharacterized form of PTEN has been discovered that contains 173 amino-terminal extra amino acids, as a result of an alternate translation initiation site. To facilitate research in the field and to avoid ambiguities in the naming and identification of PTEN amino acids from publications and databases, we propose here a unifying nomenclature and amino acid numbering for this longer form of PTEN.
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http://dx.doi.org/10.1126/scisignal.2005560DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4367864PMC
July 2014

Rab5 and Ndfip1 are involved in Pten ubiquitination and nuclear trafficking.

Traffic 2014 Jul 3;15(7):749-61. Epub 2014 Jun 3.

Brain Development and Regeneration Division, Florey Institute of Neuroscience and Mental Health, The University of Melbourne, Parkville, Victoria, 3010, Australia.

The spatial regulation of Pten is critical for its role as a tumour suppressor with both nuclear and cytoplasmic locations being implicated with distinct functions. In the cytoplasm, Pten plays a central role in opposing PI3K/Akt cell signalling, whereas in the nucleus, Pten is important for maintaining genome stability and enhancing the tumour suppressor activity of APC-CDH1. Despite this diversity in protein function at different subcellular locations, there is limited knowledge on how Pten is able to find different cellular niches. Here, we report that Rab5 GTPase is required for efficient trafficking and ubiquitination of Pten on endosomes inside the cytosol. Using bimolecular fluorescence complementation (BiFC) for imaging protein interactions, we observed that ubiquitinated Pten is localized to peri-nuclear and nuclear regions of the cell. Nuclear trafficking of Pten required both Rab5 as well as the E3 ligase adaptor protein Ndfip1. Rab5 colocalization with Pten was observed on endosomes and expression of a dominant negative form of Rab5 significantly reduced Pten ubiquitination and nuclear trafficking. Genomic deletion of Ndfip1 abrogated nuclear trafficking of ubiquitinated Pten, even in the presence of Rab5. Our findings show that endosomal trafficking and ubiquitination are important mechanisms for the subcellular distribution of Pten.
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http://dx.doi.org/10.1111/tra.12175DOI Listing
July 2014

Ndfip1 mediates peripheral tolerance to self and exogenous antigen by inducing cell cycle exit in responding CD4+ T cells.

Proc Natl Acad Sci U S A 2014 Feb 13;111(6):2067-74. Epub 2014 Jan 13.

John Curtin School of Medical Research, Australian National University, Canberra, ACT 2601, Australia.

The NDFIP1 (neural precursor cell expressed, developmentally down-regulated protein 4 family-interacting protein 1) adapter for the ubiquitin ligase ITCH is genetically linked to human allergic and autoimmune disease, but the cellular mechanism by which these proteins enable foreign and self-antigens to be tolerated is unresolved. Here, we use two unique mouse strains--an Ndfip1-YFP reporter and an Ndfip1-deficient strain--to show that Ndfip1 is progressively induced during T-cell differentiation and activation in vivo and that its deficiency causes a cell-autonomous, Forkhead box P3-independent failure of peripheral CD4(+) T-cell tolerance to self and exogenous antigen. In small cohorts of antigen-specific CD4(+) cells responding in vivo, Ndfip1 was necessary for tolerogen-reactive T cells to exit cell cycle after one to five divisions and to abort Th2 effector differentiation, defining a step in peripheral tolerance that provides insights into the phenomenon of T-cell anergy in vivo and is distinct from the better understood process of Bcl2-interacting mediator of cell death-mediated apoptosis. Ndfip1 deficiency precipitated autoimmune pancreatic destruction and diabetes; however, this depended on a further accumulation of nontolerant anti-self T cells from strong stimulation by exogenous tolerogen. These findings illuminate a peripheral tolerance checkpoint that aborts T-cell clonal expansion against allergens and autoantigens and demonstrate how hypersensitive responses to environmental antigens may trigger autoimmunity.
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http://dx.doi.org/10.1073/pnas.1322739111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3926078PMC
February 2014

Increased Ndfip1 in the substantia nigra of Parkinsonian brains is associated with elevated iron levels.

PLoS One 2014 24;9(1):e87119. Epub 2014 Jan 24.

Florey Institute of Neuroscience and Mental Health, The University of Melbourne, Parkville, Australia.

Iron misregulation is a central component in the neuropathology of Parkinson's disease. The iron transport protein DMT1 is known to be increased in Parkinson's brains linking functional transport mechanisms with iron accumulation. The regulation of DMT1 is therefore critical to the management of iron uptake in the disease setting. We previously identified post-translational control of DMT1 levels through a ubiquitin-mediated pathway led by Ndfip1, an adaptor for Nedd4 family of E3 ligases. Here we show that loss of Ndfip1 from mouse dopaminergic neurons resulted in misregulation of DMT1 levels and increased susceptibility to iron induced death. We report that in human Parkinson's brains increased iron concentrations in the substantia nigra are associated with upregulated levels of Ndfip1 in dopaminergic neurons containing α-synuclein deposits. Additionally, Ndfip1 was also found to be misexpressed in astrocytes, a cell type normally devoid of this protein. We suggest that in Parkinson's disease, increased iron levels are associated with increased Ndfip1 expression for the regulation of DMT1, including abnormal Ndfip1 activation in non-neuronal cell types such as astrocytes.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0087119PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3901732PMC
February 2015

Amino acid signatures in the developing mouse retina.

Int J Dev Neurosci 2014 Apr 22;33:62-80. Epub 2013 Dec 22.

School of Optometry and Vision Science, University of New South Wales, Sydney, NSW, Australia; Department of Optometry and Vision Science, University of Auckland, Auckland, New Zealand; Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Australia; Centre for Eye Health, Sydney, Australia. Electronic address:

This study characterizes the developmental patterns of seven key amino acids: glutamate, γ-amino-butyric acid (GABA), glycine, glutamine, aspartate, alanine and taurine in the mouse retina. We analyze amino acids in specific bipolar, amacrine and ganglion cell sub-populations (i.e. GABAergic vs. glycinergic amacrine cells) and anatomically distinct regions of photoreceptors and Müller cells (i.e. cell bodies vs. endfeet) by extracting data from previously described pattern recognition analysis. Pattern recognition statistically classifies all cells in the retina based on their neurochemical profile and surpasses the previous limitations of anatomical and morphological identification of cells in the immature retina. We found that the GABA and glycine cellular content reached adult-like levels in most neurons before glutamate. The metabolic amino acids glutamine, aspartate and alanine also reached maturity in most retinal cells before eye opening. When the overall amino acid profiles were considered for each cell group, ganglion cells and GABAergic amacrine cells matured first, followed by glycinergic amacrine cells and finally bipolar cells. Photoreceptor cell bodies reached adult-like amino acid profiles at P7 whilst Müller cells acquired typical amino acid profiles in their cell bodies at P7 and in their endfeet by P14. We further compared the amino acid profiles of the C57Bl/6J mouse with the transgenic X-inactivation mouse carrying the lacZ gene on the X chromosome and validated this animal model for the study of normal retinal development. This study provides valuable insight into normal retinal neurochemical maturation and metabolism and benchmark amino acid values for comparison with retinal disease, particularly those which occur during development.
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http://dx.doi.org/10.1016/j.ijdevneu.2013.12.005DOI Listing
April 2014

Nuclear trafficking of Pten after brain injury leads to neuron survival not death.

Exp Neurol 2014 Feb 22;252:37-46. Epub 2013 Nov 22.

Brain Development and Regeneration Laboratory, The Florey Institute of Neuroscience and Mental Health, The University of Melbourne, Parkville, Australia. Electronic address:

There is controversy whether accumulation of the tumor suppressor PTEN protein in the cell nucleus under stress conditions such as trauma and stroke causes cell death. A number of in vitro studies have reported enhanced apoptosis in neurons possessing nuclear PTEN, with the interpretation that its nuclear phosphatase activity leads to reduction of the survival protein phospho-Akt. However, there have been no in vivo studies to show that nuclear PTEN in neurons under stress is detrimental. Using a mouse model of injury, we demonstrate here that brain trauma altered the nucleo-cytoplasmic distribution of Pten, resulting in increased nuclear Pten but only in surviving neurons near the lesion. This event was driven by Ndfip1, an adaptor and activator of protein ubiquitination by Nedd4 E3 ligases. Neurons next to the lesion with nuclear PTEN were invariably negative for TUNEL, a marker for cell death. These neurons also showed increased Ndfip1 which we previously showed to be associated with neuron survival. Biochemical assays revealed that overall levels of Pten in the affected cortex were unchanged after trauma, suggesting that Pten abundance globally had not increased but rather Pten subcellular location in affected neurons had changed. Following experimental injury, the number of neurons with nuclear Pten was reduced in heterozygous mice (Ndfip1(+/-)) although lesion volumes were increased. We conclude that nuclear trafficking of Pten following injury leads to neuron survival not death.
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http://dx.doi.org/10.1016/j.expneurol.2013.11.017DOI Listing
February 2014

The zinc finger transcription factor RP58 negatively regulates Rnd2 for the control of neuronal migration during cerebral cortical development.

Cereb Cortex 2015 Mar 1;25(3):806-16. Epub 2013 Oct 1.

Florey Institute of Neuroscience and Mental Health, Genetics Lane, The University of Melbourne, Parkville, Melbourne, VIC 3010, Australia.

The zinc finger transcription factor RP58 (also known as ZNF238) regulates neurogenesis of the mouse neocortex and cerebellum (Okado et al. 2009; Xiang et al. 2011; Baubet et al. 2012; Ohtaka-Maruyama et al. 2013), but its mechanism of action remains unclear. In this study, we report a cell-autonomous function for RP58 during the differentiation of embryonic cortical projection neurons via its activities as a transcriptional repressor. Disruption of RP58 expression alters the differentiation of immature neurons and impairs their migration and positioning within the mouse cerebral cortex. Loss of RP58 within the embryonic cortex also leads to elevated mRNA for Rnd2, a member of the Rnd family of atypical RhoA-like GTPase proteins important for cortical neuron migration (Heng et al. 2008). Mechanistically, RP58 represses transcription of Rnd2 via binding to a 3'-regulatory enhancer in a sequence-specific fashion. Using reporter assays, we found that RP58 repression of Rnd2 is competed by proneural basic helix-loop-helix transcriptional activators. Finally, our rescue experiments revealed that negative regulation of Rnd2 by RP58 was important for cortical cell migration in vivo. Taken together, these studies demonstrate that RP58 is a key player in the transcriptional control of cell migration in the developing cerebral cortex.
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http://dx.doi.org/10.1093/cercor/bht277DOI Listing
March 2015

Metabolic profiling of the mouse retina using amino acid signatures: insight into developmental cell dispersion patterns.

Exp Neurol 2013 Dec 13;250:74-93. Epub 2013 Sep 13.

Department of Optometry and Vision Science, University of Auckland, Auckland, New Zealand.

Pattern recognition has been used for the complete and statistically rigid classification of retinal neurons in vertebrates such as the adult cat, primate, rat and goldfish. Here, we label the mouse retina with antibodies against seven amino acids and use pattern recognition to characterize distinct retinal neurochemical cell classes based on their unique amino acid signatures. We followed the development of the cell classes in the X-inactivation transgenic mouse expressing the lacZ reporter gene on one X-chromosome. This mouse allows clonally related cells to be identified through differential β-galactosidase activity due to random X-chromosome inactivation. Pattern recognition analysis partitioned the retina into nine neuronal classes at birth, increasing to 19 classes at eye opening and 26 classes by adulthood. Emergence of new cell classes was partly attributed to new neuron types and partly to the splitting of classes from early ages from refinement of their amino acid profiles. All six GABAergic amacrine cell classes and most ganglion cell classes appeared by P7 whilst all the glycinergic amacrine cell classes did not appear till adulthood. Separable bipolar cell classes were not detected till eye opening. Photoreceptor cell classes were detected at P3 but inner and outer segments did not form separable classes until adulthood. More importantly, we show that cells which share common amino acid profiles also shared cell dispersion patterns. GABAergic amacrine cell classes with conventional and displaced counterparts transgressed clonal boundaries whereas GABAergic amacrine cell classes found exclusively in the inner nuclear layer and all glycinergic amacrine cell classes did not transgress. Ganglion cells displayed both dispersion patterns. This study provides a comprehensive neurochemical atlas of the developing mouse retina, tracking the amino acid levels within distinct neuronal populations and highlighting unique migratory patterns within subpopulations of inner retinal neurons.
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http://dx.doi.org/10.1016/j.expneurol.2013.09.007DOI Listing
December 2013

Ndfip1 expression in developing neurons indicates a role for protein ubiquitination by Nedd4 E3 ligases during cortical development.

Neurosci Lett 2013 Oct 13;555:225-30. Epub 2013 Sep 13.

Brain Development and Regeneration Laboratory, The Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville 3010, Australia.

During development, protein substrates need to be removed and degraded when they are no longer required. The E3 ubiquitin ligases, including Nedd4 family proteins, are a major group of enzymes responsible for adding ubiquitin chains to protein substrates prior to their degradation. Ndfip1 (Nedd4 family-interacting protein 1) is an adaptor and activator for Nedd4-family ubiquitin ligases for increasing substrate specificity. To study Nedd4-mediated ubiquitination during cortical development, we have mapped the spatio-temporal dynamics of Ndfip1 protein expression by immunocytochemistry. Ndfip1 expression was observed from embryonic day 11 (E11.5) until adult stages. Its presence increased during the postnatal stages and peaked at postnatal day 7 (P7). Spatially, Ndfip1 was found in the ventricular and marginal zones during corticogenesis but also in the cortical plate and subplate during midstage cortical development (E15.5). Postnatally, Ndfip1 was expressed in all cortical neurons (but not in glial cells) and this expression was both ubiquitous and uniform across cortical layers involving both pyramidal and non-pyramidal neurons. This consistent but dynamic pattern of Ndfip1 expression in temporal and spatial domains of the cortical landscape is indicative of complex programs of protein ubiquitination during corticogenesis.
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http://dx.doi.org/10.1016/j.neulet.2013.09.017DOI Listing
October 2013

Ndfip1 is required for the development of pyramidal neuron dendrites and spines in the neocortex.

Cereb Cortex 2014 Dec 29;24(12):3289-300. Epub 2013 Jul 29.

Florey Institute of Neuroscience and Mental Health and.

Ubiquitin ligases of the Nedd4 family are important for axon and dendrite development, but little is known about their adaptor, Nedd4 family-interacting protein 1 (Ndfip1), that is responsible for their enzymatic activation. To study the function of Ndfip1 in cortical development, we generated a conditional knock-out (conditional KO) in neurons. The Ndfip1 conditional KO mice were viable; however, cortical neurons in the adult brain exhibited atrophic characteristics, including stunted dendritic arbors, blebbing of dendrites, and fewer dendritic spines. In electron micrographs, these neurons appeared shrunken with compacted somata and involutions of the nuclear membrane. In culture, Ndfip1 KO neurons exhibited exuberant sprouting suggesting loss of developmental control. Biochemical analysis of postsynaptic density (PSD) fractions from Ndfip1 KO cortical and hippocampal neurons showed that the postsynaptic proteins (Arc and PSD-95) were reduced compared with wild-type controls. In addition, the PI3 kinase/Akt signaling pathway was altered. These results indicate that Ndfip1, through its Nedd4 effectors, is important for the development of dendrites and dendritic spines in the cortex.
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http://dx.doi.org/10.1093/cercor/bht191DOI Listing
December 2014

Exogenous Reelin modifies the migratory behavior of neurons depending on cortical location.

Cereb Cortex 2014 Nov 7;24(11):2835-47. Epub 2013 Jun 7.

Brain Development and Regeneration Division, The Florey Institute of Neuroscience and Mental Health, Centre for Neuroscience, University of Melbourne, Parkville, Victoria, Australia and.

Malformations of cortical development can arise when projection neurons generated in the germinal zones fail to migrate properly into the cortical plate. This process is critically dependent on the Reelin glycoprotein, which when absent leads to an inversion of cortical layers and blurring of borders. Reelin has other functions including supporting neuron migration and maintaining their trajectories; however, the precise role on glial fiber-dependent or -independent migration of neurons remains controversial. In this study, we wish to test the hypothesis that migrating cortical neurons at different levels of the cortical wall have differential responses to Reelin. We exposed neurons migrating across the cortical wall to exogenous Reelin and monitored their migratory behavior using time-lapse imaging. Our results show that, in the germinal zones, exogenous Reelin retarded neuron migration and altered their trajectories. This behavior is in contrast to the response of neurons located in the intermediate zone (IZ), possibly because Reelin receptors are not expressed in this zone. In the reeler cortex, Reelin receptors are expressed in the IZ and exposure to exogenous Reelin was able to rescue the migratory defect. These studies demonstrate that migrating neurons have nonequivalent responses to Reelin depending on their location within the cortical wall.
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http://dx.doi.org/10.1093/cercor/bht123DOI Listing
November 2014

Perturbations in cortical development and neuronal network excitability arising from prenatal exposure to benzodiazepines in mice.

Eur J Neurosci 2013 May 4;37(10):1584-93. Epub 2013 Mar 4.

The Australian Regenerative Medicine Institute, Monash University, Clayton, Victoria, Australia.

During brain development, many factors influence the assembly and final positioning of cortical neurons, and this process is essential for proper circuit formation and normal brain function. Among many important extrinsic factors that guide the maturation of embryonic cortical neurons, the secreted neurotransmitter GABA has been proposed to influence both their migratory behaviour and their terminal differentiation. The full extent of the short-term and long-term changes in brain patterning and function caused by modulators of the GABA system is not known. In this study, we specifically investigated whether diazepam, a commonly used benzodiazepine that modulates the GABAA receptor, alters neuronal positioning in vivo, and whether this can lead to lasting effects on brain function. We found that fetal exposure to diazepam did not change cell positioning within the embryonic day (E)14.5 mouse cerebral cortex, but significantly altered neuron positioning within the E18.5 cortex. In adult mice, diazepam treatment affected the distribution of cortical interneurons that express parvalbumin or calretinin, and also led to a decrease in the numbers of calretinin-expressing interneurons. In addition, we observed that neonatal exposure to diazepam altered the sensitivity of mice to a proconvulsant challenge. Therefore, exposure of the fetal brain to benzodiazepines has consequences for the positioning of neurons and cortical network excitability.
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http://dx.doi.org/10.1111/ejn.12167DOI Listing
May 2013

The new Fandangle.

Authors:
Seong-Seng Tan

Aust Orthod J 2012 Nov;28(2):265

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November 2012

The tumor suppressor PTEN is exported in exosomes and has phosphatase activity in recipient cells.

Sci Signal 2012 Sep 25;5(243):ra70. Epub 2012 Sep 25.

Brain Development and Regeneration Division, Florey Neuroscience Institutes, The University of Melbourne, Parkville, Victoria 3010, Australia.

Exosomes are microvesicles of endosomal origin that are secreted, and their contents (proteins, lipids, DNA, or microRNAs) can alter the physiological states of recipient cells. We demonstrated that phosphatase and tensin homolog deleted on chromosome 10 (PTEN), a tumor suppressor protein normally localized in the cytoplasm and nucleus, was secreted in exosomes. Secreted PTEN was internalized by recipient cells with resultant functional activity, which resulted in reduced phosphorylation of the serine and threonine kinase Akt and reduced cellular proliferation. PTEN secretion in exosomes required Ndfip1, an adaptor protein for members of the Nedd4 family of E3 ubiquitin ligases. Without Ndfip1, neither Nedd4-1 nor Nedd4-2 promoted the recruitment of PTEN into exosomes. In addition, lysine 13 within PTEN, which is required for its ubiquitination by Nedd4-1, was required for exosomal transport of PTEN. These results implicate Ndfip1 as a molecular regulator of the exosomal export of PTEN, with consequences for non-cell-autonomous PTEN activity. Thus, we suggest that the ability of PTEN to exert phosphatase activity beyond the cell in which it is produced has implications for PTEN function during development, health, and disease.
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http://dx.doi.org/10.1126/scisignal.2003084DOI Listing
September 2012

Differential regulation of Nedd4 ubiquitin ligases and their adaptor protein Ndfip1 in a rat model of ischemic stroke.

Exp Neurol 2012 May 5;235(1):326-35. Epub 2012 Mar 5.

Brain Development and Regeneration Laboratory, Florey Neuroscience Institutes, The University of Melbourne, Parkville, Australia.

Ubiquitin-modification of proteins by E3 ubiquitin ligases is an important post-translational mechanism implicated in neuronal survival and injury following cerebral ischemia. However, of the 500 or so E3s thought to be present in mammalian cells, very few specific E3s have been identified and associated with brain ischemia. Here, we demonstrate endogenous induction of HECT-type E3 ligases of the Nedd4 family and their adaptor Nedd4-family interacting protein 1 (Ndfip1) following transient focal cerebral ischemia in rats. Ndfip1 is upregulated in surviving cortical neurons and its neuroprotective activity is correlated with Nedd4-2 upregulation, but not two other Nedd4 family members examined (Nedd4-1 and Itch). Immunoprecipitation assays confirmed biochemical binding of Ndfip1 with Nedd4-2 in the brain, with or without ischemic stroke, indicating their endogenous interaction. While Ndfip1 and Itch have been previously shown to interact outside of the nervous system, ischemic induction of Itch in the present study was associated with cellular survival independent of Ndfip1. Together, these findings demonstrate specific and differential regulation of Nedd4 family E3 ligases under ischemic conditions, and identify two E3 ligases and their adaptor that potentially regulate ubiquitination in ischemic stroke to provide neuroprotection.
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http://dx.doi.org/10.1016/j.expneurol.2012.02.014DOI Listing
May 2012

Cyclin D2 in the basal process of neural progenitors is linked to non-equivalent cell fates.

EMBO J 2012 Apr 6;31(8):1879-92. Epub 2012 Mar 6.

Division of Developmental Neuroscience, United Core Centers for Advanced Research and Translational Medicine, Tohoku University Graduate School of Medicine, Sendai, Japan.

Asymmetric cell division plays an indispensable role during corticogenesis for producing new neurons while maintaining a self-renewing pool of apical progenitors. The cellular and molecular determinants favouring asymmetric division are not completely understood. Here, we identify a novel mechanism for generating cellular asymmetry through the active transportation and local translation of Cyclin D2 mRNA in the basal process. This process is regulated by a unique cis-regulatory sequence found in the 3' untranslated region (3'UTR) of the mRNA. Unequal inheritance of Cyclin D2 protein to the basally positioned daughter cell with the basal process confers renewal of the apical progenitor after asymmetric division. Conversely, depletion of Cyclin D2 in the apically positioned daughter cell results in terminal neuronal differentiation. We demonstrate that Cyclin D2 is also expressed in the developing human cortex within similar domains, thus indicating that its role as a fate determinant is ancient and conserved.
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http://dx.doi.org/10.1038/emboj.2012.43DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3343330PMC
April 2012

Ndfip1 regulates nuclear Pten import in vivo to promote neuronal survival following cerebral ischemia.

J Cell Biol 2012 Jan 2;196(1):29-36. Epub 2012 Jan 2.

Brain Development and Regeneration Laboratory, Florey Neuroscience Institutes, The University of Melbourne, Parkville, Victoria 3010, Australia.

PTEN (phosphatase and tensin homologue deleted on chromosome TEN) is the major negative regulator of phosphatidylinositol 3-kinase signaling and has cell-specific functions including tumor suppression. Nuclear localization of PTEN is vital for tumor suppression; however, outside of cancer, the molecular and physiological events driving PTEN nuclear entry are unknown. In this paper, we demonstrate that cytoplasmic Pten was translocated into the nuclei of neurons after cerebral ischemia in mice. Critically, this transport event was dependent on a surge in the Nedd4 family-interacting protein 1 (Ndfip1), as neurons in Ndfip1-deficient mice failed to import Pten. Ndfip1 binds to Pten, resulting in enhanced ubiquitination by Nedd4 E3 ubiquitin ligases. In vitro, Ndfip1 overexpression increased the rate of Pten nuclear import detected by photobleaching experiments, whereas Ndfip1(-/-) fibroblasts showed negligible transport rates. In vivo, Ndfip1 mutant mice suffered larger infarct sizes associated with suppressed phosphorylated Akt activation. Our findings provide the first physiological example of when and why transient shuttling of nuclear Pten occurs and how this process is critical for neuron survival.
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http://dx.doi.org/10.1083/jcb.201105009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3255971PMC
January 2012

Cellular up-regulation of Nedd4 family interacting protein 1 (Ndfip1) using low levels of bioactive cobalt complexes.

J Biol Chem 2011 Mar 27;286(10):8555-64. Epub 2010 Dec 27.

School of Chemistry, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Parkville 3010, Victoria, Australia.

The delivery of metal ions using cell membrane-permeable metal complexes represents a method for activating cellular pathways. Here, we report the synthesis and characterization of new [Co(III)(salen)(acac)] complexes capable of up-regulating the ubiquitin ligase adaptor protein Ndfip1. Ndfip1 is a neuroprotective protein that is up-regulated in the brain after injury and functions in combination with Nedd4 ligases to ubiquitinate harmful proteins for removal. We previously showed that Ndfip1 can be increased in human neurons using CoCl(2) that is toxic at high concentration. Here we demonstrate a similar effect can be achieved by low concentrations of synthetic Co(III) complexes that are non-toxic and designed to be activated following cellular entry. Activation is achieved by intracellular reduction of Co(III) to Co(II) leading to release of Co(II) ions for Ndfip1 up-regulation. The cellular benefit of Ndfip1 up-regulation by Co(III) complexes includes demonstrable protection against cell death in SH-SY5Y cells during stress. In vivo, focal delivery of Co(III) complexes into the adult mouse brain was observed to up-regulate Ndfip1 in neurons. These results demonstrate that a cellular response pathway can be advantageously manipulated by chemical modification of metal complexes, and represents a significant step of harnessing low concentration metal complexes for therapeutic benefit.
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http://dx.doi.org/10.1074/jbc.M110.203448DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3048738PMC
March 2011

Altered speeds and trajectories of neurons migrating in the ventricular and subventricular zones of the reeler neocortex.

Cereb Cortex 2011 May 16;21(5):1018-27. Epub 2010 Sep 16.

Howard Florey Institute, Florey Neuroscience Institutes, Parkville, Victoria 3010, Australia.

The Reelin signaling pathway is essential for proper cortical development, but it is unclear to whether Reelin function is primarily important for cortical layering or neuron migration. It has been proposed that Reelin is perhaps required only for somal translocation but not glial-dependent locomotion. This implies that the location of neurons responding to Reelin is restricted to the outer regions of the cortical plate (CP). To determine whether Reelin is required for migration outside of the CP, we used time-lapse imaging to track the behavior of cells undergoing locomotion in the germinal zones. We focused on the migratory activity in the ventricular/subventricular zones where the first transition of bipolar to multipolar migration occurs and where functional Reelin receptors are known to be expressed. Despite Reelin loss, neurons had no difficulty in undergoing radial migration and indeed displayed greater migratory speed. Additionally, compared with the wild-type, reeler neurons displayed altered trajectories with greater deviation from a radial path. These results suggest that Reelin loss has early consequences for migration in the germinal zones that are portrayed as defective radial trajectories and migratory speeds. Together, these abnormalities can give rise to the increased cell dispersion observed in the reeler cortex.
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http://dx.doi.org/10.1093/cercor/bhq168DOI Listing
May 2011

Spatiotemporal regulation of multiple overlapping sense and novel natural antisense transcripts at the Nrgn and Camk2n1 gene loci during mouse cerebral corticogenesis.

Cereb Cortex 2011 Mar 6;21(3):683-97. Epub 2010 Aug 6.

Department of Molecular Pathology, The Institute of Medical and Veterinary Science, Adelaide, SA 5000, Australia.

Nrgn and Camk2n1 are highly expressed in the brain and play an important role in synaptic long-term potentiation via regulation of Ca(2+)/calmodulin-dependent protein kinase II. We have shown that the gene loci for these 2 proteins are actively transcribed in the adult cerebral cortex and feature multiple overlapping transcripts in both the sense and antisense orientations with alternative polyadenylation. These transcripts were upregulated in the adult compared with embryonic and P1.5 mouse cerebral cortices, and transcripts with different 3' untranslated region lengths showed differing expression profiles. In situ hybridization (ISH) analysis revealed spatiotemporal regulation of the Nrgn and Camk2n1 sense and natural antisense transcripts (NATs) throughout cerebral corticogenesis. In addition, we also demonstrated that the expression of these transcripts was organ-specific. Both Nrgn and Camk2n1 sense and NATs were also upregulated in differentiating P19 teratocarcinoma cells. RNA fluorescent ISH analysis confirmed the capability of these NATs to form double-stranded RNA aggregates with the sense transcripts in the cytoplasm of cells obtained from the brain. We propose that the differential regulation of multiple sense and novel overlapping NATs at the Nrgn and Camk2n1 loci will increase the diversity of posttranscriptional regulation, resulting in cell- and time-specific regulation of their gene products during cerebral corticogenesis and function.
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http://dx.doi.org/10.1093/cercor/bhq141DOI Listing
March 2011