My research group studies mouse models with vestibular (inner ear) defects that may provide insights into balance disorders in humans. I am focusing on mutations that affect the structure and function of the otolithic end organs, small inner-ear structures that act as linear acceleration and gravity receptors. We have identified and characterized genes that are defective in head-tilt (het), head-slant (hslt), and neuromutagenesis facility (nmf) 333 mutant mice, each of which encodes an NADPH oxidase component. Thus, we've hypothesized that a previously unknown inner ear NADPH oxidase complex is necessary for proper development and function of the vestibular system.
I am also studying a mouse model that exhibits sex reversal, craniofacial defects, and shortening of the limbs characteristic of some forms of human dwarfism. We have narrowed the genetic defect to a region on mouse Chromosome 7 and are analyzing that region of the genome with the goal of better understanding dwarfism and certain skeletal malformation syndromes in humans.
Genetics and genomics of mouse vestibular and skeletal development
Genetics of vestibular development
The vestibular system is the portion of the inner ear required for maintaining balance, sensing bodily orientation, and detecting gravity. To further our understanding of the vestibular system and its disorders, I am studying several mouse strains harboring mutations that affect the structure and function of the otolithic end organs. These small structures, found within the inner ear, act as linear acceleration and gravity receptors. When stimulated by straight-line movements or the force of gravity, these receptors transmit signals along the vestibular nerve to the brain. Mice with mutations disrupting this pathway display a number of behaviors indicative of vestibular dysfunction. These include an abnormal tilting posture, inability to swim, impaired ground and air righting reflexes, circling behaviors, and elevation or absence of vestibular-evoked potential (VsEP) thresholds. By studying mice with vestibular impairment, we hope to better understand the development and maintenance of the otolithic organs and their relationship to human vestibular disorders.
In 2004, in collaboration with colleagues at Ingenium Pharmaceuticals AG, in Martinsried, Germany, we identified mutations within the NADPH oxidase 3 (Nox3) gene as the underlying basis of the head tilt (het) mutant phenotype. Additional studies by us, and others, have identified the causative mutation in the NADPH oxidase organizer 1 (Noxo1) gene underlying the head slant (hslt) mutant phenotype. As a direct result of these studies, we have hypothesized that a previously unknown NADPH oxidase complex is present within the inner ear, and that it is required for normal development and function of the vestibular system.
We have further hypothesized that the inner ear NADPH oxidase complex may show many parallels to the well-characterized, bacteria-killing NADPH oxidase complex of neutrophils. Defects in any of various components of this immune complex result in chronic granulomatous disease (CGD) and can lead to life-threatening bacterial and fungal infections unless treated with aggressive antibiotic therapy.
Based on this hypothesis, recent studies in collaboration with Dr. Botond Banfi at the University of Iowa and Dr. Sherri M. Jones at East Carolina University have confirmed the cytochrome b-245, alpha polypeptide (Cyba) gene as a product deficient in some forms of CGD, and as a third gene product required for otolithic end organ development. Additional studies in collaboration with Dr. Sherri M. Jones at East Carolina University are aimed at identifying additional loci throughout the genome that affect age-related aspects of vestibular dysfunction. Together, these studies explore the structural and functional development of the vestibular system in the embryo and maintenance of the vestibular system in the adult.
Genetics of skeletal development
Sox genes serve as key regulators in many developmental processes including sex determination and skeletal development. To better understand these roles, I have begun a series of experiments designed to elucidate the molecular basis of a disproportionate dwarfism occurring in some strains of SrySox3 transgenic mice.
Sry normally initiates male gonadal development. SrySox3 describes a family of Sry transgenes containing the HMG DNA binding domain of Sox3. When expressed at high enough levels, these transgenes direct male sexual development in chromosomally female (XX) mice, indicating that Sox3 HMG domains can bind to and activate Sry target sequences. For one SrySox3 integrant Tg(SrySox3)77Ei or Tg77 mice homozygous for the transgene display not only the expected sex reversal, but surprisingly, also exhibit a form of rhizomelic (limb-shortening) dwarfism (rhizomelia, rzm). Mechanistically, this dwarfism could result from either a gain-of-function (ectopic expression of the transgene) or loss-of-function (interruption of a gene at the point of integration) phenomenon. Analysis of animals containing rzm/Tg77 in trans to an encompassing deletion should distinguish between these two hypotheses. In initial mapping experiments conducted in collaboration with Dr. Eva Eicher, rzm was localized to a region of Chromosome 7 near the mouse Sox6 gene. Refined mapping, in combination with current genome assemblies, has narrowed rzm to a 5.6 Mbp (approximately 2.3 cM) region contained within a single contiguous sequence. In addition, several BACs within the immediate region have been retrofitted with selectable markers, making them suitable for introduction into the mouse germline using embryonic stem (ES) cell technologies. It is possible that one of these BACs could rescue the rzm phenotype. Further experiments are designed to clone the region immediately adjacent to the transgene integration to understand the exact molecular defect underlying the dwarfism phenotype. At that point, I can begin to explore any parallels that may exist at the molecular genetic level between rzm in mice and certain poorly understood skeletal malformation syndromes in humans.
Principal Investigator: David E. Bergstrom, Ph.D.
Research Assistant III: Tiffany Leidy-Davis
Research Assistant II: Louise Dionne, Heather Fairfield
Biomedical Technologist III: Belinda Harris
Biomedical Technologist II: Son Yong Karst
Laboratory Technician IV: Leslie L. Haynes
Executive Assistant: Aimée Picard
Davisson MT, Bergstrom DE, Reinholdt LG, Donahue LR. Discovery Genetics: The History and Future of Spontaneous Mutation Research, Curr Protocol Mouse Biol. 2012; 2:103-118.
Fairfield H, Gilbert G, Barter M, Corrigan RR, Curtain M, Ding Y, D’Ascenzo M, Gerhardt, D, He C, Huang W, Richmond T, Rowe LB, Probst FJ, Bergstrom DE, Murray SA, Bult C, Richardson J, Kile B, Gut I, Hager J, Sigurdsson S, Mauceli E, Di Palma F, Lindblad-Toh K, Cunningham ML, Cox TC, Justice MJ, Spector MS, Lowe SW, Albert T, Donahue LR, Jeddeloh J, Shendure J, Reinholdt LG. 2011. Functional Genomics in Mice by Whole Exome Sequencing. Genome Biol. 12(9):R86. PMCID: PMC3308049
Flaherty JP, Fairfield HE, Spruce CA, McCarty CM, Bergstrom DE. 2011. Molecular characterization of an allelic series of mutations in the mouse Nox3 gene. Mamm Genome 22(3-4):156-69. PMCID: PMC3056917
Flaherty JP, Spruce CA, Fairfield HE, Bergstrom DE. 2010. Generation of a conditional null allele of NADPH oxidase activator 1 (Noxa1). Genesis 48:568-575. PMCID: PMC3009462
Nakano Y, Longo-Guess CM, Bergstrom DE, Nauseef WM, Jones SM, Banfi B. 2008. Mutation of the Cyba gene encoding p22phox causes vestibular and immune defects in mice. J Clin Invest 118:1176-1185. PMCID: PMC2248803
Longo-Guess C, Gagnon LH, Bergstrom DE, Johnson. 2007. A missense mutation in the conserved C2B domain of otoferlin causes deafness in a new mouse model of DFNB9. Hear Res 234:21-28. PMCID: PMC2140949
Paffenholz R, Bergstrom RA, Pasutto F, Wabnitz P, Munroe RJ, Jagla W, Heinzmann U, Marquart A, Bareiss A, Laufs J, Russ A, Stumm G, Schimenti JC, Bergstrom DE. 2004. Vestibular defects in head-tilt mice result from mutations in Nox3, encoding an NADPH oxidase. Genes Dev 18:486-491.
Bergstrom D, Bergstrom R, Munroe R, Lee B, Browning V, You Y, Eicher E, Schimenti J. 2003. Overlapping deletions spanning the proximal two-thirds of the mouse t complex. Mamm Genome 14:817-829.
Bergstrom DE. 2002. Haplotype. In: Encyclopedia of Genetics, Brenner S, Miller JH, (eds). Academic Press, Boston, MA, pp. 911-912.
Bergstrom DE. 2002. Recombination Suppression. In: Encyclopedia of Genetics. Brenner S, Miller JH (eds). Academic Press, Boston, MA, pp. 1648-1649.
Bergstrom DE, Young M, Albrecht KH, Eicher E. 2000. Related function of mouse SOX3, SOX9, and SRY HMG domains assayed by male sex determination. Genesis 28:111-124.
Bergstrom DE, Gagnon LH, Eicher EM. 1999. Genetic and physical mapping of the dreher locus on mouse Chromosome 1. Genomics 59:291-299.
Bergstrom DE, Grieco DA, Sonti MM, Fawcett JJ, Bell-Prince C, Cram LS, Narayanswami S, Simpson EM. 1998. The mouse Y Chromosome: Enrichment, sizing, and cloning by bivariate flow cytometry. Genomics 48:304-313.
Bergstrom DE, Yan H, Sonti MM, Narayanswami S, Bayleran JK, Simpson EM. 1997. An expanded collection of mouse Y Chromosome RDA clones. Mamm Genome 8:510-512.
Merli C, Bergstrom DE, Cygan JA, Blackman RK. 1996. Promoter specificity mediates the independent regulation of neighboring genes. Genes Dev 10:1260-1270.
Bergstrom DE, Merli CA, Cygan JA, Shelby R, Blackman RK. 1995. Regulatory autonomy and molecular characterization of the Drosophila out at first gene. Genetics 139:1331-1346.