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Immunogenetics

One of the key challenges in medical research is to elucidate the factors that increase an individual’s risk for developing disease. The focus of my group is identifying how sequence variation for certain genes affects the immune system and increases susceptibility to autoimmune and infectious diseases. It is estimated that autoimmune diseases, such as type 1 diabetes, affect ~4% of the population. During the course of evolution it might be assumed that genetic variation conferring susceptibility for autoimmune disease would undergo negative selection. However, genome-wide association studies and the relatively high prevalence of autoimmune disease suggest that susceptibility alleles are common within the human population. One explanation is that these susceptibility alleles are maintained because they provide resistance to infectious disease. Nevertheless, studying this dichotomy in humans is difficult due to genetic heterogeneity and tissue availability. Instead, mouse models have been widely used to better understand the genetics and disease pathology of infection and autoimmunity. Our principal research strategy is to use the parallel characterization of type 1 diabetes and bacterial infection in mice to facilitate the identification of disease-related genes, as well as determine if bacterial infection can modulate the immune system and potentially prevent autoimmune disease.

Research Themes

Genomic and functional analyses of a type 1 diabetes genes

Group Leader: Dr Tom Brodnicki
Team Members: Ms Iris Tan, Ms Michelle Ashton, Ms Leanne Mackin, Dr Colleen Elso, Mr Sean Ivory, Mr Edward Chu
Collaborators: Meredith O’Keeffe (Burnet Institute), Ken Shortman & Li Wu (The Walter & Eliza Hall Institute)

Despite the recent success of human genetic studies for type 1 diabetes (T1D), there have been limits to translating these findings into a better understanding of disease susceptibility and pathogenesis.  In some cases, the contribution of identified genes is not clear and still requires basic biological studies, which are not possible in human subjects.  An excellent animal model for studying the role of T1D susceptibility genes is the nonobese diabetic (NOD) mouse.  Similar to humans affected by this autoimmune disease, NOD mice suffer from destruction of insulin-producing beta cells mediated by autoreactive lymphocytes.  The goal of this work is to identify and characterize genes using the NOD mouse model to better understand which genes in humans contribute to T1D.

We have recently used selective mating and genetic studies of NOD mice to discover a novel gene, which we have temporarily named Latet (Latin for “to be unknown”).  Comparison of this gene between different mouse strains identified a mutation associated with T1D.  As the function of this gene is currently unknown, we have used molecular techniques to disrupt this gene in a mouse strain that doesn’t develop T1D.  It is not necessarily expected that this “knockout mouse” will develop T1D because multiple genes contribute to diabetes onset.  However, these mice may exhibit abnormalities in their immune system, which will provide clues as to how this gene contributes to T1D susceptibility in NOD mice.  At present, the human equivalent for this gene is also unknown, but cross-species comparison of genomic sequence suggests that a human version of Latet exists.  We are currently using a number of molecular and cellular techniques to determine the function of this gene in mice with the ultimate aim of identifying its potential role in humans affected by T1D.         

How does bacterial infection affect type 1 diabetes susceptibility?

Group Leader: Dr Tom Brodnicki
Team Members: Ms Nancy Wang, Ms Leanne Mackin, Mr Sean Ivory
Collaborators: Odilia Wijburg & Dick Strugnell (The University of Melbourne)

It has been observed that the incidence of type 1 diabetes (T1D) is escalating in developed countries.  It is unlikely this escalation is due to an increase in gene mutations that confer susceptibility for T1D.  Rather, the declining incidence of infectious diseases in these countries may provide an alternative explanation.  Although hotly debated, the hygiene hypothesis suggests that certain childhood infections may temper the immune system and trigger a protective mechanism against autoimmunity in those individuals who have inherited T1D susceptibility genes.  Nonetheless, it seems unexpected that elimination of infectious diseases might leave the immune system free to attack the insulin-producing beta cells.  This paradox is difficult to study in humans.  Instead, inbred mouse strains can be used to investigate genetic and environmental factors contributing to autoimmune diseases, such as T1D.

One of the best animal models for T1D is the nonobese diabetic (NOD) mouse.  We have recently confirmed that NOD mice are more susceptible to certain bacterial infections.  The goal of this project is to determine why NOD mice are more susceptible to bacterial infection compared to other mouse strains.  Furthermore, we aim to investigate the hypothesis that bacterial infection can alter T1D susceptibility in NOD mice depending on the time and dose of infection.  Characterization of the genes and immune cell subsets, which contribute to bacterial susceptibility in NOD mice, may elucidate biological mechanisms that can be targeted to prevent T1D in at-risk individuals. 

Accelerating disease gene discovery: Transposon mutagenesis in mice

Group Leader: Dr Tom Brodnicki
Team Members: Dr Colleen Elso, Mr Sean Ivory, Ms Michelle Ashton, Mr Pravin Rajasekaran

A major challenge for complex genetic disease research is to identify genes, or their encoded products, that can be therapeutically targeted to prevent disease.  Unfortunately, allelic variation for genes identified in genome-wide association studies often has subtle biological effects.  An alternative approach is to identify those genes that, when disrupted, prevent disease.  The recent development of the Sleeping Beauty (SB) transposon system and its ability to mutate the mouse germline provides a powerful tool for the disruption and efficient identification of such genes.  We have recently established this system in the nonobese diabetic (NOD) mouse strain, which is predisposed to different autoimmune diseases with complex genetic aetiology, including type 1 diabetes, Sjogren’s syndrome, and thyroiditis. 

 

To generate transposon-mutant NOD mice, we have established transgenic NOD lines that harbour the two components of the transposon system: the transposon tag and the enzyme that catalyses transposon jumping.  Offspring from selected mating of these lines can be efficiently screened for transposition events using a fluorescent marker located within the transposon.  Hence, mice that harbour transposon-disrupted genes “glow”.  A pilot study has already yielded fluorescent NOD mice.  A distinct advantage of this system is that disrupted gene(s) can be identified using the transposon tag long before characterizing mice for disease-related traits.  Thus, transposon-disrupted genes within large numbers of fluorescent mice can be assessed for their potential role in disease pathogenesis and prioritized for analysis.  This strategy aims to maximise our chance of gene discovery for different diseases in NOD mice, as well as demonstrate the utility of SB mutagenesis as a tool for dissecting complex genetic diseases.

Honours and PhD Projects

Staff

  • Dr Tom Brodnicki
  • Dr Colleen Elso
  • Edward Chu
  • May Abdulaziz Alsayb
  • Leanne Mackin

Publication Highlights

  1. N Wang, C Elso, L Mackin, SI Mannering, RA Strugnell, OL Wijburg, TC Brodnicki (2014) Congenic NOD mice reveal genetic epistasis and overlapping loci for autoimmune diabetes and listeriosis.  Immunogenetics  66: 501-506
  2. N Wang, RA Strugnell, O Wijburg, TC Brodnicki (2014) Systemic infection of mice with Listeria monocytogenes to characterize host immune responses.  In Methods in Molecular Biology: Mouse Models of Innate Immunity, 1031: 125-144
  3. A-N Pelletier, F Guimont-Desrochers, M Ashton, TC Brodnicki, S Lesage (2012) The size of the plasmacytoid dendritic cell compartment is a multigenetic trait dominated by a locus on mouse chromosome 7.  Journal of Immunology 188: 5561-5570
  4. J Liu, MP Ashton, H Sumer, MK O’Bryan, TC Brodnicki, PJ Verma (2011) Generation of stable pluripotent stem cells from non-obese diabetic (NOD) mouse tail-tip fibroblasts.  Diabetes  60: 1393-1398
  5. N Wang, L Mackin, RA Strugnell, O Wijburg, TC Brodnicki (2011) Measuring bacterial load and immune cells in mice infected with Listeria monocytogenes.  Journal of Visual Experiments 54 (http://www.jove.com/details.php?id=3076  doi: 10.3791/3076)
  6. KLI Tan, L Mackin, N Wang, AT Papenfuss, C Elso, M Ashton, F Quirk, B Phipson, M Bahlo, TP Speed, G Smyth, G Morahan, TC Brodnicki (2010) A recombination hotspot leads to sequence variability within a novel gene (AK005651) and contributes to type 1 diabetes susceptibility.  Genome Research 20: 1629-1638
  7. Burt RA, L Walkins, IKL Tan, N Wang, L Mackin, F Quirk, P Morgn, J-G Zang, G Morahan, SP Berzins, TC Brodnicki (2010) An NZW-derived interval on chromosome 7 moderates sialadenitis, but not insulitis in NOD mice.  Journal of Immunology 184: 859-868
  8. MC Jawahar*, TC Brodnicki*, F Quirk, YM Wilson, M Murphy (2008) Behavioural analysis of congenic mouse strains confirms stress-responsive loci on chromosomes 1 and 12.  Behavior Genetics 38:407-416 (*MC Jawahar and TC Brodnicki are co-first authors)
  9. TC Brodnicki  (2007) Somatic Mutation and Autoimmunity.  Cell 131: 1220-1221
  10. DKY Ang*, TC Brodnicki*, WE Wilson, P Silveira, BL Gliddon, MA Jordan, AG Baxter, IR van Driel  (2007) Two Genetic Loci Independently Confer Susceptibility to Autoimmune Gastritis.  International Immunology 19: 1135-1144.  (*DKY Ang and TC Brodnicki are co-first authors)
  11. N Armstrong, TC Brodnicki, TP Speed (2006) Mind the Gap:  Analysis of Marker-Assisted Breeding Strategies for Inbred Mouse Strains.  Mammalian Genome 17: 273-287
  12. TC Brodnicki, K O’Donnell, F Quirk, DM Tarlinton (2006) Congenic NOD Mouse Strains Fail to Confirm Linkage of a Marginal Zone B Lymphocyte Phenotype to the Idd11 Locus on Chromosome 4.  Journal of Immunology 176: 701-702