Overview
Our lab uses mouse models to identify the molecular pathways underlying degenerative motor neuron diseases in humans, such as spinal muscular atrophy (SMA) and amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig's disease). We cloned the gene for neuromuscular degeneration to create a mouse model for a lethal infantile form of SMA known as spinal muscular atrophy with respiratory distress. Studying the mouse model led to the identification of a modifier gene that decreases disease severity in the mice. In addition, we are working with a transgenic mouse strain (SOD1) to study genetic background effects on progression of an ALS-like disease in the mouse model.
We are also studying mouse models for degenerative muscle diseases similar to muscular dystrophy in humans. We cloned a genetic defect and have localized the mutation to the muscle-specific titin gene, the largest known coding gene in the mammalian genome. The mouse strain is a novel model of progressive muscular dystrophy and may also be a model for human tibial muscular dystrophy and limb-girdle muscular dystrophy type 2J. We also identified the mutation for a new form of rostrocaudal muscular dystrophy that affects skeletal muscle tissues in a unusual front-to-back progression.
Research details
Mouse Models of Neuromuscular Disease
The long-term goal of our research program is to identify molecular pathways necessary for the normal function and survival of motor neurons and their skeletal muscle targets. Muscular dystrophies and motor neuron diseases collectively have a high impact on health, affecting tens of thousands of people in the United States alone. The diseases are characterized by weakness and progressive wasting of muscles, eventually leading to paralysis and death. We have chosen to focus on the resources available at The Jackson Laboratory in the form of spontaneous and induced models of neuromuscular disease as our starting point for gene discovery and functional analysis. This phenotype-driven approach ensures that the mutant genes we identify are critical for the normal development and/or maintenance of motor neurons and skeletal muscles.
A mouse model of spinal muscular atrophy with respiratory distress
Neuromuscular degeneration, nmd, is a spontaneous autosomal recessive mouse mutant characterized by severe hindlimb muscle atrophy due to progressive degeneration of spinal motor neurons. We identified the mutant nmd gene as immunoglobulin mu binding protein 2 (Ighmbp2), a member of the DNA helicase/ATPase family of proteins. Mutations in the human IGHMBP2 gene have been shown to cause a lethal infantile form of spinal muscular atrophy with respiratory distress (SMARD1). As the nmd mice develop the same motor neuron disease as children with SMARD1, we are hopeful that what we learn from these mice will be directly relevant to the human disease. Toward this goal, we are employing powerful genetic approaches to identify the critical cell types that require Ighmbp2 gene activity in transgenic mice. We have demonstrated that tissue-specific expression of IGHMBP2 in neurons completely rescues the motor neuron degeneration, but it also uncovered a previously unrecognized requirement for this gene product in cardiac muscle. The transgenic nmd mice show no signs of paralysis but do develop a progressive dilated cardiomyopathy (DCM). Similarly, skeletal and cardiac-specific Ighmbp2 transgenic lines rescue the cardiomyopathy independent of the motor neurons and increased the lifespan of nmd mice up to 8-fold.
Identifying a genetic modifier of nmd
The effects of modifier genes in human cases of amyotrophic lateral sclerosis (ALS) or spinal muscular atrophy (SMA) have been implied when intrafamilial heterogeneity in age of onset or severity of symptoms are encountered. However, the possible multifactorial nature of these modifiers and genetic heterogeneity among families limit the extent to which genetic linkage can be performed in human populations. During the course of fine-mapping the nmd gene, we identified a modifier gene on Chromosome 13 that greatly decreases the severity of disease. We have generated a B6 congenic mouse strain that contains the CAST-derived Mnm modifier locus to allow high-resolution genetic mapping and positional cloning. We have reduced the size of the genetic region that is known to contain the Mnm modifier gene to a 160 kb interval, and the disease can be completely suppressed using a CAST BAC clone as a transgene. Our ability to manipulate the severity of disease with at least one modifier gene suggests that a molecular pathway exists with the potential for genetic or clinical intervention.
Mapping genetic modifiers of amyotrophic lateral sclerosis
Along with colleague Kevin Seburn at The Jackson Laboratory, we are testing the hypothesis that genetic background effects can modify the onset or progression of ALS symptoms in the G93A mutant SOD1 transgenic mouse model. Using a strain survey with several wild-derived and common inbred strains of mice, we have identified two inbred strains (ALR/LtJ and NOD/LtJ) that significantly accelerate the onset of disease and three that significantly delay disease onset (C57BL/6J, DBA/2J and BALB/cByJ). Reciprocal backcrosses between C57BL/6J and ALR/LtJ have permitted the mapping of quantitative trait loci that underlie the suppression or enhancement of the motor neuron disease in G93A SOD1 (Tg(SOD1-G93A)1Gur) transgenic mice. Identification of these polymorphic loci is likely to provide insights into the mechanism of disease and possible genetic targets for intervention.
Defining the functional role of titin in mdm muscular dystrophy
Muscular dystrophy with myositis (mdm) is an autosomal recessive mutation located on Chromosome 2 that leads to progressive degeneration of skeletal muscles. We identified the mdm mutation as a deletion and truncated LINE insertion in the muscle-specific titin (Ttn) gene and have explored its potential interaction with the muscle-specific protease calpain 3. The discovery of this model at The Jackson Laboratory proved to be the first muscular dystrophy mutation identified in the Ttn gene, which encodes the largest known protein in the mammalian genome (>100 kb mRNA, ~370 exons, 3.7 megadalton protein). The mdm mouse serves as a model for human limb-girdle muscular dystrophy 2J and tibial muscular dystrophy. We are currently generating an allelic series of muscular dystrophy mutations at the Ttn locus using a sensitized ENU mutagenesis screen to identify critical functional or ligand-binding domains as well as defining the role of TTN in muscle cell development and degenerative muscular dystrophies.
A novel disease mechanism identified in rostrocaudal muscular dystrophy (rmd)
Rostrocaudal muscular dystrophy (rmd) is a new recessive mouse mutation that causes a rapidly progressive muscular dystrophy and a neonatal forelimb bone deformity. We identified the rmd mutation in the choline kinase beta (Chkb) gene, resulting in a complete loss of CHKB protein and enzymatic activity. Choline kinase catalyzes the phosphorylation of choline to phosphocholine in the biosynthesis of the major membrane phospholipid phosphatidylcholine (PC). While mutant rmd mice show a dramatic decrease of CHK activity in all tissues, the dystrophy is only evident in skeletal muscle tissues in an unusual rostral-to-caudal gradient. Enlarged mitochondria are evident in rmd muscles, suggesting that dysregulation of energy metabolism may underlie the muscle disease. The rmd mutant mouse offers the first demonstration of a defect in a phospholipid biosynthetic enzyme causing muscular dystrophy.
Lab staff
Research Scientist: Kevin L. Seburn, Ph.D.
Postdoctoral Fellows: Kimberly A. Huebsch, Ph.D., T, Roger B. Sher, Ph.D., Patricia Schroder, Ph.D.
Research Assistant: David G. Schroeder, B.S.
Research Administrative Assistant: Ashley Stanton
Publication listings
Chamberlain JS, Farwell NJ, Ranier JE, Cox GA, Caskey CT. 1991. PCR analysis of dystrophin gene mutation and expression. J.Cell Biochem. 46:255-259.
Cox GA, Phelps SF, Chapman VM, Chamberlain JS. 1993. New mdx mutation disrupts expression of muscle and nonmuscle isoforms of dystrophin. Nature Genetics 4:87-93.
Cox GA, Cole NM, Matsumura K, Phelps SF, Hauschka SD, Campbell KP, Faulkner JA, Chamberlain JS. 1993. Overexpression of dystrophin in transgenic mdx mice eliminates dystophic symptoms without toxicity. Nature 364:725-729.
Denetclaw WF, Jr., Hopf FW, Cox GA, Chamberlain JS, Steinhardt RA. 1994. Myotubes from transgenic mdx mice expressing full-lenght dystrophin show normal calcium regulation. Mol. Biol. Cell 5:1159-1167.
Cox GA, Sunada Y, Campbell KP, Chamberlain JS. 1994. Dp71 can restore the dystrophin-associated glycoprotein complex in muscle but fails to prevent dystrophy. Nature Genetics 8:333-339.
Rafael JA, Cox GA, Corrado K, Jung D, Campbell KP, Chamberlain JS. 1996. Forced expression of dystrophin deletion constructs reveals structure-function correlations. J. Cell Biol. 134:93-102.
Cox GA, Lutz CM, Yang C-L, Biemesderfer D, Bronson RT, Fu, A, Aronson PS, Noebels JL, Frankel WN. 1997. Sodium/hydrogen exchanger gene defect in slow-wave epilepsy mutant mice. Cell 91:139-148.
Cox GA, Mahaffey CL, Frankel WN. 1998. Identification of the mouse neuromuscular degeneration gene and mapping of a second site suppressor allele. Neuron 21:1327-1337.
Lumerg CN, Phelps SF, Rafael JA, Cox GA, Hutchinson TL, Begy CR, Adkins E, Wiltshire R, Chamberlain JS. 1999. Characterization of dystrophin and utrophin diversity in the mouse. Hum. Mol. Genet. 8:593-599.
Cox GA, Mahaffey CL, Nystuen A, Letts VA, Frankel WN. 2000. The mouse fidgetin gene defines a new role for AAA family proteins in mammalian development. Nat. Genet. 26:198-202.
Sundberg JP, Boggess D, Shultz LD, Fijneman RJ, Demant P, HogenEsch H, Cox GA. 2000. The chronic proliferative dermatitis mouse mutation (cpdm): mapping of the mutant gene locus. J Exp Anim Sci 41:101-108.
Garvey SM, Rajan C, Lerner AP, Frankel WN, Cox GA. 2002. The Muscular Dystrophy with myositis (mdm) mouse mutation disrupts a skeletal muscle-specific domain of titin. Genomics 79:146-149.
Sundberg JP, Boggess D, Silva KA, McElwee KJ, King LE, Li R, Churchill G, Cox GA. 2003. Major locus on mouse chromosome 17 and minor locus on chromosome 9 are linked with alopecia areata in C3H/HeJ mice. J. Invest. Dermatol. 120:771-775.
Serreze DV, Pierce MA, Post CM, Chapman HD, Savage H, Bronson RT, Rothman PB, Cox GA. 2003. Paralytic autoimmune myositis develops in addition to type 1 diabetes in NOD mice made Th1 cytokin deficient by expression of an IFNg receptor β chain transgene. J Immunology 170:2742-2749.
Maddatu TP, Garvey SM, Shroeder DG, Hampton TG, Cox GA. 2004. Transgenic rescue of neurogenic atrophy in the nmd mouse reveals a role for Ighmbp2 in dilated cardiomyopathy. Hum. Mol. Genet. 13:1105-1115.
Sunberg JP, Silva KA, Li R, Cox GA, King LE. 2004. Adult onset alopecia areata is a complex polygenic trait in the C3H/HeJ mouse model. J. Invest. Dermatol. 123:294-297.
Ho M, Post CM, Donahue LR, Lidov HGW, Bronson RT, Goolsby H, Watkins SC, Cox GA, Brown RH Jr. 2004. Disruption of muscle membrane and phenotype divergence in two mouse models of dysferlin-deficiency. Hum. Mol. Genet. 13:1999-2010.
Wooley CM, Sher RB, Kale A, Frankel WN, Cox GA, Seburn KL. 2005. Gait analysis detects early changes in transgenic SOD1(G93A) mice. Muscle Nerve. 32:43-50.
Lee Y, Kameya S, Cox GA, Hsu J, Hicks W, Maddatu TP, Smith RS, Naggert JK, Peachey NS, Nishina PM. 2005. Ocular abnormalities in Large (myd) and Large (vls) mice, spontaneous models in muscle, eye, and brain diseases. Mol Cell Neurosci Oct;30(2):160-72.
Huebsch KA, Kudryashova E, Wooley CM, Sher RB, Seburn KL, Spencer MJ, Cox GA. 2005. Mdm Muscular Dystrophy: Interactions with Calpain 3 and a Novel Functional Role for Titin's N2A Domain. Hum Mol Genet Oct 1;14(19):2801-11.
Maddatu TP, Garvey SM, Schroeder DG, Zhang W, Kim SY, Nicholson AI, Davis CJ, Cox GA. 2005. Dilated cardiomyopathy in the nmd mouse: transgenic rescue and QTLs that improve cardiac function and survival Hum Mol Genet. Nov 1;14(21):3179-89.
Hadano S, Benn SC, Kakuta S, Otomo A, Sudo K, Kunita R, Suzuki-Utsunomiya K, Mizumura H, Shefner JM, Cox GA, Iwakura Y, Brown RH Jr, Ikeda JE. 2006. Mice deficient in the Rab5 guanine nucleotide exchange factor ALS2/alsin exhibit age-dependent neurological deficits and altered endosome trafficking Hum Mol Genet. Jan 15;15(2):233-50.
Tarchini B, Huynh TH, Cox GA, Duboule D. 2005. HoxD cluster scanning deletions identify multiple defects leading to paralysis in the mouse mutant Ironside. Genes Dev. Dec 1;19(23):2862-76.
Sher RB, Aoyama C, Huebsch KA, Ji S, Kerner J, Yang Y, Frankel WN, Hoppel CL, Wood PA, Vance DE, Cox GA. 2006. A rostrocaudal muscular dystrophy caused by a defect in choline kinase beta, the first enzyme in phosphatidylcholine biosynthesis. J Biol Chem. Feb 24;281(8):4938-48.
Mikaelian I, Hovick M, Silva KA, Burzenski LM, Shultz LD, Ackert-Bicknell CL, Cox GA, Sundberg JP. 2006 Expression of terminal differentiation proteins defines stages of mouse mammary gland development. Vet Pathol. Jan;43(1):36-49.
Runkel F, Bussow H, Seburn KL, Cox GA, Ward DM, Kaplan J, Franz T. 2006. Grey, a novel mutation in the murine Lyst gene, causes the beige phenotype by skipping of exon 25. Mamm Genome Mar;17(3):203-10.
Seburn KL, Nangle LA, Cox GA, Schimmel P, Burgess RW. 2006. An active dominant mutation of glycyl-tRNA synthetase causes neuropathy in a Charcot-Marie-Tooth 2D mouse model. Neuron Sep 21;51(6):715-26.
Seymour RE, Hasham MG, Cox GA, Shultz LD, Hogenesch H, Roopenian DC, Sundberg JP. 2007. Spontaneous mutations in the mouse Sharpin gene result in multiorgan inflammation, immune system dysregulation and dermatitis. Genes Immun. Jul;8(5):416-21.
Yang Y, Mahaffey CL, Berube N, Maddatu TP, Cox GA, Frankel WN. 2007. Complex seizure disorder caused by Brunol4 deficiency in mice. PLoS Genet. Jul 27;3(7):e124.
Books, Book Chapters and Reviews
Chamberlain JS, Phelps SF, Cox GA, Maichele AJ, Greenwood AD. 1993. PCR analysis of muscular dystrophoy in mdx mice. In: Molecular and Cell Biology of Muscular Dystrophy, Partridge T (ed), Chapman & Hall. 167-189.
Chamberlain JS, Corrado K, Rafael JA, Cox GA, Hauser M, Lumeng C. 1997. Interactions between dystrophin and the sarcolemma membrane. In: Cytoskeletal Regulation of Membrane Function (ed. Froehner SC and Bennett V, The Rockefeller University Press, New York): 19-29
