James M Murphy

The Walter and Eliza Hall Institute of Medical Research, Melbourne, Victoria, Australia

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Publications (44)255.19 Total impact

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    ABSTRACT: Interleukin-3 (IL-3) is a cytokine secreted by mast cells and activated T-cells known to be an important regulator of differentiation, survival, proliferation and activation of a range of hematopoietic lineages. The effects of IL-3 on target cells are mediated by a transmembrane receptor system composed of a cytokine-specific α-subunit and a β-subunit, the principal signalling entity. In the mouse, two β-subunits have co-evolved: a common β-subunit (βc) shared between IL-3 and the related cytokines, IL-5 and GM-CSF; and an IL-3-specific β-subunit (βIL-3). βIL‑3 differs from βc in its specificity for IL-3 and its capacity to bind IL-3 directly in the absence of an α-subunit and, in the absence of structural information, the basis for these properties has remained enigmatic. Here, we present the crystal structure of the βIL-3 ectodomain at 3.45 Å resolution. This structure provides the first evidence that βIL-3 adopts an arch-shaped, intertwined homodimer with similar topology to the paralogous βc structure. In contrast to apo-βc, however, the ligand-binding interface of βIL‑3 appears to pre-exist in a conformation receptive to IL-3 engagement. Molecular modelling of the IL-3:βIL‑3 interface, in conjunction with previous mutational studies, suggests that divergent evolution of both βIL‑3 and IL-3 underlies their unique capacity for direct interaction and specificity.
    The Biochemical journal. 08/2014;
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    ABSTRACT: The JAK (Janus kinase) family members serve essential roles as the intracellular signalling effectors of cytokine receptors. This family, comprising JAK1, JAK2, JAK3 and TYK2 (tyrosine kinase 2), was first described more than 20 years ago, but the complexities underlying their activation, regulation and pleiotropic signalling functions are still being explored. Here, we review the current knowledge of their physiological functions and the causative role of activating and inactivating JAK mutations in human diseases, including haemopoietic malignancies, immunodeficiency and inflammatory diseases. At the molecular level, recent studies have greatly advanced our knowledge of the structures and organization of the component FERM (4.1/ezrin/radixin/moesin)-SH2 (Src homology 2), pseudokinase and kinase domains within the JAKs, the mechanism of JAK activation and, in particular, the role of the pseudokinase domain as a suppressor of the adjacent tyrosine kinase domain's catalytic activity. We also review recent advances in our understanding of the mechanisms of negative regulation exerted by the SH2 domain-containing proteins, SOCS (suppressors of cytokine signalling) proteins and LNK. These recent studies highlight the diversity of regulatory mechanisms utilized by the JAK family to maintain signalling fidelity, and suggest alternative therapeutic strategies to complement existing ATP-competitive kinase inhibitors.
    The Biochemical journal. 08/2014; 462(1):1-13.
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    ABSTRACT: Upon ligand binding, RIPK1 is recruited to tumor necrosis factor receptor superfamily (TNFRSF) and Toll-like receptor (TLR) complexes promoting prosurvival and inflammatory signaling. RIPK1 also directly regulates caspase-8-mediated apoptosis or, if caspase-8 activity is blocked, RIPK3-MLKL-dependent necroptosis. We show that C57BL/6 Ripk1(-/-) mice die at birth of systemic inflammation that was not transferable by the hematopoietic compartment. However, Ripk1(-/-) progenitors failed to engraft lethally irradiated hosts properly. Blocking TNF reversed this defect in emergency hematopoiesis but, surprisingly, Tnfr1 deficiency did not prevent inflammation in Ripk1(-/-) neonates. Deletion of Ripk3 or Mlkl, but not Casp8, prevented extracellular release of the necroptotic DAMP, IL-33, and reduced Myd88-dependent inflammation. Reduced inflammation in the Ripk1(-/-)Ripk3(-/-), Ripk1(-/-)Mlkl(-/-), and Ripk1(-/-)Myd88(-/-) mice prevented neonatal lethality, but only Ripk1(-/-)Ripk3(-/-)Casp8(-/-) mice survived past weaning. These results reveal a key function for RIPK1 in inhibiting necroptosis and, thereby, a role in limiting, not only promoting, inflammation.
    Cell 05/2014; · 31.96 Impact Factor
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    ABSTRACT: Loss of Inhibitor of Apoptosis (IAP) proteins, particularly cIAP1, can promote production of tumor necrosis factor (TNF) and sensitize cancer cell lines to TNF induced necroptosis by promoting formation of a death inducing signaling complex containing receptor-interacting serine/threonine-protein kinase 1 and 3 (RIPK1, RIPK3). To define the role of IAPs in myelopoiesis, we generated a mouse with cIAP1, cIAP2 and XIAP deleted in the myeloid lineage. Loss of cIAPs and XIAP in the myeloid lineage caused over-production of many pro-inflammatory cytokines, resulting in granulocytosis and severe sterile inflammation. In vitro differentiation of macrophages from bone marrow in the absence of cIAPs and XIAP led to detectable levels of TNF and resulted in reduced numbers of mature macrophages. The cytokine production and consequent cell death caused by IAP depletion was attenuated by loss or inhibition of TNF or TNFR1. The loss of RIPK1 or RIPK3, but not the RIPK3 substrate MLKL, attenuated TNF secretion and thereby prevented apoptotic cell death and not necrosis. Our results demonstrate that cIAPs and XIAP together restrain RIPK1 and RIPK3 dependent cytokine production in myeloid cells to critically regulate myeloid homeostasis.
    Blood 02/2014; · 9.78 Impact Factor
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    ABSTRACT: Necroptosis describes a pro-inflammatory form of cell death governed by the kinases RIP1 and RIP3. Necroptosis can occur following stimulation of the DNA receptor, DAI, or activation of death receptor, Toll-like receptor, T-cell antigen receptor, or interferon receptor signaling. Analysis of RIP3 deficient mice has implicated necroptosis in several inflammatory-driven diseases, including atherosclerosis, alcoholic liver disease and retinal degeneration. Although studies have demonstrated that mixed lineage kinase domain-like (MLKL) is the only substrate of RIP3 kinase that is essential for necroptotic death, the molecular determinants acting downstream of MLKL remain ambiguous. In addition, RIP3 can signal necroptosis independent of RIP1, may induce apoptosis, and can directly promote pro-inflammatory cytokine production. Therefore it will be important to determine if non-necroptotic RIP3 signaling influences RIP3 dependent pathologies.
    Current opinion in immunology 02/2014; 26C:76-89. · 10.88 Impact Factor
  • James M Murphy, John Silke
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    ABSTRACT: When our time comes to die most people would probably opt for a quick, peaceful and painless exit. But the manner and timing are rarely under our direct control. Hence the Ars moriendi, literally, "The Art of Dying", two texts written in Latin around the 15th century that offered advice on how to die well according to the Christian ideals of the time. In contrast, for individual cells, the death process is frequently under their control and several signaling pathways that cause cell death, including apoptosis, pyroptosis and necroptosis, have been described. Furthermore the manner in which cells die can have good or bad consequences for the organism. In this review we will discuss how cells die via the necroptotic signaling pathway, with emphasis on recent structural work and place this work in a biological context by discussing relevant studies with knock-out animals.
    EMBO Reports 01/2014; · 7.19 Impact Factor
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    ABSTRACT: Abstract Activation of the cell surface receptor, c-Mpl, by the cytokine, thrombopoietin (TPO), underpins megakaryocyte and platelet production in mammals. In humans, mutations in c-Mpl have been identified as the molecular basis of Congenital Amegakaryocytic Thrombocytopenia (CAMT). Here, we show that CAMT-associated mutations in c-Mpl principally lead to defective receptor presentation on the cell surface. In contrast, one CAMT mutant c-Mpl, F104S, was expressed on the cell surface, but showed defective TPO binding and receptor activation. Using mutational analyses, we examined which residues adjacent to F104 within the membrane-distal cytokine receptor homology module (CRM) of c-Mpl comprise the TPO-binding epitope, revealing residues within the predicted Domain 1 E-F and A-B loops and Domain 2 F'-G' loop as key TPO-binding determinants. These studies underscore the importance of the c-Mpl membrane-distal CRM to TPO-binding and suggest that mutations within this CRM that perturb TPO binding could give rise to CAMT.
    Growth factors (Chur, Switzerland) 01/2014; · 2.47 Impact Factor
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    ABSTRACT: JAK2 (Janus kinase 2) initiates the intracellular signalling cascade downstream of cell surface receptor activation by cognate haematopoietic cytokines, including erythropoietin and thrombopoietin. The pseudokinase (JH2) domain of JAK2 negatively regulates the catalytic activity of the adjacent tyrosine kinase (JH1) domain and mutations within the pseudokinase domain underlie human myeloproliferative neoplasms, including polycythaemia vera and essential thrombocytosis. To date, the mechanism of JH2-mediated inhibition of JH1 kinase activation as well as the susceptibility of pathological mutant JAK2 to inhibition by the physiological negative regulator, SOCS3, have remained unclear. Here, using recombinant, purified JAK2JH1-JH2 proteins, we demonstrate that, when activated, wild-type and myeloproliferative neoplasm-associated mutants of JAK2 exhibit comparable enzymatic activity and inhibition by SOCS3 in in vitro kinase assays. Small angle X-ray scattering (SAXS) showed that JAK2JH1-JH2 exists in an elongated configuration in solution with no evidence for interaction between JH1 and JH2 domains in cis. Collectively, these data are consistent with a model in which JAK2's pseudokinase domain binds and inhibits the activation of the tyrosine kinase domain of a neighbouring JAK2 molecule within a cytokine receptor complex, but does not influence the activity of JAK2 once it has been activated. Our data indicate that, in the absence of the N-terminal FERM domain and thus cytokine receptor association, the wild-type and pathological mutants of JAK2 are enzymatically equivalent and equally susceptible to inhibition by SOCS3.
    Biochemical Journal 12/2013; · 4.65 Impact Factor
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    ABSTRACT: The pseudokinase, Mixed lineage kinase domain-like (MLKL), was recently identified as an essential checkpoint in the programmed necrosis or "necroptosis" cell death pathway. Here, we present the crystal structure of the human MLKL pseudokinase domain at 1.7 Å resolution and probe its nucleotide-binding mechanism by performing structure-based mutagenesis. By comparing the structures and nucleotide binding determinants of human and mouse MLKL orthologues, our study provides insights into the evolution of nucleotide binding mechanisms amongst pseudokinases and their mechanistic divergence from conventional, catalytically-active protein kinases.
    Biochemical Journal 11/2013; · 4.65 Impact Factor
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    ABSTRACT: Protein kinase-like domains that lack conserved residues known to catalyze phosphoryl transfer, termed pseudokinases, have emerged as important signaling domains across the kingdoms of life. Although predicted to function principally as catalysis-independent protein interaction modules, several pseudokinase domains have been attributed unexpected catalytic functions, often amidst controversy. We established a thermal stability shift assay as a benchmark technique to define the nucleotide binding properties of kinase-like domains. Unlike in vitro kinase assays, this assay is insensitive to the presence of minor quantities of contaminating kinases that may otherwise lead to incorrect attributions of catalytic functions to pseudokinases. We demonstrated the utility of this method by classifying 31 diverse pseudokinase domains into four groups: devoid of detectable nucleotide or cation binding; cation-independent nucleotide binding; cation binding; or nucleotide binding enhanced by cations. While nine pseudokinases bound ATP in a divalent cation-dependent manner, over half of those examined did not detectably bind nucleotides, illustrating that pseudokinase domains predominantly function as non-catalytic protein interaction modules within signaling networks and that only a small subset is potentially catalytically active. We propose that henceforth the thermal shift assay be adopted as the standard technique for establishing the nucleotide binding and catalytic potential of kinase-like domains.
    Biochemical Journal 10/2013; · 4.65 Impact Factor
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    ABSTRACT: Mixed lineage kinase domain-like (MLKL) is a component of the "necrosome," the multiprotein complex that triggers tumor necrosis factor (TNF)-induced cell death by necroptosis. To define the specific role and molecular mechanism of MLKL action, we generated MLKL-deficient mice and solved the crystal structure of MLKL. Although MLKL-deficient mice were viable and displayed no hematopoietic anomalies or other obvious pathology, cells derived from these animals were resistant to TNF-induced necroptosis unless MLKL expression was restored. Structurally, MLKL comprises a four-helical bundle tethered to the pseudokinase domain, which contains an unusual pseudoactive site. Although the pseudokinase domain binds ATP, it is catalytically inactive and its essential nonenzymatic role in necroptotic signaling is induced by receptor-interacting serine-threonine kinase 3 (RIPK3)-mediated phosphorylation. Structure-guided mutation of the MLKL pseudoactive site resulted in constitutive, RIPK3-independent necroptosis, demonstrating that modification of MLKL is essential for propagation of the necroptosis pathway downstream of RIPK3.
    Immunity 09/2013; · 19.80 Impact Factor
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    ABSTRACT: JAKs (Janus kinases) are essential mediators of almost all biological signalling events initiated by haemopoietic and immune cytokines. However, aberrant and/or prolonged JAK-induced signalling is detrimental and can give rise to a number of inflammatory and proliferative pathologies. For this reason, the tyrosine kinase activity of the JAKs is carefully regulated at a number of different levels. Primarily, this is achieved by: (i) ensuring that the catalytic domain is 'switched off' under basal conditions, and (ii) inhibiting the activity of JAK after it has been switched on. Whereas the first mode of inhibition is mediated by JAK's own pseudokinase domain as well as the action of phosphatases, the second is achieved by the action of the SOCS (suppressor of cytokine signalling) proteins, negative-feedback inhibitors of JAK-mediated signalling. The present review focuses on the mode of action of SOCS1 and SOCS3, the two most potent JAK inhibitors.
    Biochemical Society Transactions 08/2013; 41(4):1042-7. · 2.59 Impact Factor
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    ABSTRACT: Approximately 10% of the human kinome has been classified as pseudokinases due to the absence of one or more of three motifs known to play key roles in the catalytic activities of protein kinases. Structural and functional studies are now emerging, reclassifying this 'dead' kinase family as essential signalling molecules that act as crucial modulators of signal transduction. This raises the prospect that pseudokinases may well represent an as-yet-unexplored class of drug targets. However, the extent to which nucleotide binding and catalytic activity contribute to the biological functions of pseudokinases remains an area of great controversy. In the present review, we discuss the advantages and disadvantages of the different methods employed to characterize the nucleotide-binding properties and activity of pseudokinases.
    Biochemical Society Transactions 08/2013; 41(4):975-80. · 2.59 Impact Factor
  • Patrick A Eyers, James M Murphy
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    ABSTRACT: Recent studies of proteins containing kinase-like domains that lack catalytic residue(s) classically required for phosphotransfer, termed pseudokinases, have uncovered important roles in cell signalling across the kingdoms of life. Additionally, mutations within pseudokinase domains are known to underlie human diseases, suggesting that these proteins may represent new and unexplored therapeutic targets. To date, few pseudokinases have been studied in intricate detail, but as described in the present article and in the subsequent papers in this issue of Biochemical Society Transactions, several new studies have provided an advanced template and an improved framework for interrogating the roles of pseudokinases in signal transduction. In the present article, we review landmarks in the establishment of this field of study, highlight some experimental challenges and propose a simple scheme for definition of these domains based on their primary sequences, rather than experimentally defined nucleotide-binding or catalytic activities.
    Biochemical Society Transactions 08/2013; 41(4):969-74. · 2.59 Impact Factor
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    ABSTRACT: Both of the TNF superfamily ligands, TNF and LTα, can bind and signal through TNFR1 and TNFR2, yet mice mutant for each have different phenotypes. Part of this difference is because LTα but not TNF can activate Herpes Virus Entry Mediator and also heterotrimerise with LTβ to activate LTβR, which is consistent with the similar phenotypes of the LTα and LTβR deficient mice. However, it has also been reported that the LTα3 homotrimer signals differently than TNF through TNFR1, and has unique roles in initiation and exacerbation of some inflammatory diseases. Our modeling of the TNF/TNFR1 interface compared to the LTα3 /TNFR1 structure revealed some differences that could affect signalling by the two ligands. To determine whether there were any functional differences in the ability of TNF and LTα3 to induce TNFR1-dependent apoptosis or necroptosis, and if there were different requirements for cIAPs and Sharpin to transmit the TNFR1 signal, we compared the ability of cells to respond to TNF and LTα3 . Contrary to our hypothesis, we were unable to discover differences in signalling by TNFR1 in response to TNF and LTα3 . Our results imply that the reasons for the conservation of LTα are most likely due either to differential regulation, the ability to signal through Herpes Virus Entry Mediator or the ability of LTα to form heterotrimers with LTβ. This article is protected by copyright. All rights reserved.
    FEBS Journal 07/2013; · 4.25 Impact Factor
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    ABSTRACT: The inhibitory protein SOCS3 plays a key part in the immune and hematopoietic systems by regulating signaling induced by specific cytokines. SOCS3 functions by inhibiting the catalytic activity of Janus kinases (JAKs) that initiate signaling within the cell. We determined the crystal structure of a ternary complex between mouse SOCS3, JAK2 (kinase domain) and a fragment of the interleukin-6 receptor β-chain. The structure shows that SOCS3 binds JAK2 and receptor simultaneously, using two opposing surfaces. While the phosphotyrosine-binding groove on the SOCS3 SH2 domain is occupied by receptor, JAK2 binds in a phosphoindependent manner to a noncanonical surface. The kinase-inhibitory region of SOCS3 occludes the substrate-binding groove on JAK2, and biochemical studies show that it blocks substrate association. These studies reveal that SOCS3 targets specific JAK-cytokine receptor pairs and explains the mechanism and specificity of SOCS action.
    Nature Structural & Molecular Biology 03/2013; · 11.90 Impact Factor
  • Jeffrey J Babon, James M Murphy
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    ABSTRACT: The discovery that a range of myeloproliferative diseases and leukemias are associated with Janus Kinase (JAK) mutations has highlighted the importance of JAK/STAT signalling in disease and sparked a renewed interest in developing JAK inhibitors. In vitro kinase assays are the most direct and quantitative method to assess mutant forms of JAK for altered enzymatic properties as well as verifying and quantifying the affinity and efficacy of potential inhibitors. Here, we describe protocols for heterologous expression and purification of JAK kinases from insect cells, assays to determine the activity of these purified kinases, and finally inhibition assays to determine the effectiveness of potential inhibitors.
    Methods in molecular biology (Clifton, N.J.) 01/2013; 967:39-55. · 1.29 Impact Factor
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    ABSTRACT: Suppressor of Cytokine Signaling (SOCS)5 is thought to act as a tumour suppressor through negative regulation of JAK/STAT and epidermal growth factor (EGF) signaling. However, the mechanism/s by which SOCS5 acts on these two distinct pathways is unclear. We show for the first time that SOCS5 can interact directly with JAK via a unique, conserved region in its N-terminus, which we have termed the JAK interaction region (JIR). Co-expression of SOCS5 was able to specifically reduce JAK1 and JAK2 (but not JAK3 or TYK2) autophosphorylation and this function required both the conserved JIR and additional sequences within the long SOCS5 N-terminal region. We further demonstrate that SOCS5 can directly inhibit JAK1 kinase activity, although its mechanism of action appears distinct from that of SOCS1 and SOCS3. In addition, we identify phosphoTyr317 in Shc-1 as a high-affinity substrate for the SOCS5-SH2 domain and suggest that SOCS5 may negatively regulate EGF and growth factor-driven Shc-1 signaling by binding to this site. These findings suggest that different domains in SOCS5 contribute to two distinct mechanisms for regulation of cytokine and growth factor signaling.
    PLoS ONE 01/2013; 8(8):e70536. · 3.53 Impact Factor
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    ABSTRACT: Human interleukin-3 (hIL-3) is a polypeptide growth factor that regulates the proliferation, differentiation, survival and function of hematopoietic progenitors and many mature blood cell lineages. Although recombinant hIL-3 is a widely used laboratory reagent in hematology, standard methods for its preparation, including those employed by commercial suppliers, remain arduous owing to a reliance on refolding insoluble protein expressed in E. coli. In addition, wild-type hIL-3 is a poor substrate for radio-iodination, which has been a long-standing hindrance to its use in receptor binding assays. To overcome these problems, we developed a method for expression of hIL-3 in E. coli as a soluble protein, with typical yields of >3mg of purified hIL-3 per litre of shaking microbial culture. Additionally, we introduced a non-native tyrosine residue into our hIL-3 analog, which allowed radio-iodination to high specific activities for receptor binding studies whilst not compromising bioactivity. The method presented herein provides a cost-effective and convenient route to milligram quantities of a hIL-3 analog with wild-type bioactivity that, unlike wild-type hIL‑3, can be efficiently radio-iodinated for receptor binding studies.
    PLoS ONE 01/2013; 8(8):e74376. · 3.53 Impact Factor
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    ABSTRACT: SMCHD1 is an epigenetic modifier of gene expression that is critical to maintain X chromosome inactivation. Here we show in the mouse that genetic inactivation of Smchd1 accelerates tumorigenesis in male mice. Loss of Smchd1 in transformed mouse embryonic fibroblasts increased tumor growth upon transplantation into immunodeficient nude mice. Additionally, loss of Smchd1 in Eµ-Myc transgenic mice that undergo lymphomagenesis reduced disease latency by 50% relative to control animals. In pre-malignant Eμ-Myc transgenic mice deficient in Smchd1, there was an increase in the number of pre-B cells in the periphery, likely accounting for the accelerated disease in these animals. Global gene expression profiling suggested that Smchd1 normally represses genes activated by MLL-chimeric fusion proteins in leukaemia, implying that Smchd1 loss may work through the same pathways as overexpressed MLL-fusion proteins do in leukaemia and lymphoma. Notably, we found that SMCHD1 is underexpressed in many types of human hematopoietic malignancy. Together, our observations collectively highlight a hitherto uncharacterized role for SMCHD1 as a candidate tumor suppressor gene in hematopoietic cancers.
    Cancer Research 12/2012; · 9.28 Impact Factor

Publication Stats

386 Citations
255.19 Total Impact Points

Institutions

  • 2009–2014
    • The Walter and Eliza Hall Institute of Medical Research
      • • Division of Cancer and Haematology
      • • Division of Molecular Medicine
      Melbourne, Victoria, Australia
    • University Health Network
      Toronto, Ontario, Canada
  • 2013
    • Adelaide Cancer Centre
      Tarndarnya, South Australia, Australia
    • Monash University (Australia)
      • Department of Biochemistry and Molecular Biology
      Melbourne, Victoria, Australia
    • University of Liverpool
      • Institute of Integrative Biology
      Liverpool, ENG, United Kingdom
  • 2012
    • University of Melbourne
      Melbourne, Victoria, Australia
  • 2003–2010
    • Australian National University
      • Molecular Bioscience Department
      Canberra, Australian Capital Territory, Australia
  • 2006–2009
    • Samuel Lunenfeld Research Institute
      Toronto, Ontario, Canada
    • University of Toronto
      • Department of Molecular Genetics
      Toronto, Ontario, Canada