Karl G. Johnson

Sarah Rempel and Herbert S. Rempel Professor of Neuroscience; On leave for the 2023-2024 academic year
  • Expertise


    Karl Johnson’s research is aimed at understanding how developing neurons find and make their appropriate synaptic connections in simple central nervous systems, using Drosophila (the common fruit fly) as a model organism. His research focuses on identifying novel genes that are essential for two aspects of nervous system development—first, how neurons find their proper synaptic targets, and second, how neurons build synapses.

    He and his team of undergraduate researchers have begun to characterize how heparan sulfate proteoglycans (HSPGs) influence central nervous system development, and are focusing their current efforts on examining the roles of two HSPGs, syndecan and dallylike, in axon guidance and synapse formation.

    Research Interests

    Johnson’s ongoing research is exploring the role a group of evolutionarily ancient molecules called heparin sulfate proteoglycans (HSPGs) play in central nervous system development in Drosophila. 

    Areas of Expertise

    • Biology
    • Molecular Biology
    • Developmental Neurobiology
    • Developmental Biology
    • Axon Guidance
  • Work


    With D. Arizanovska and J. King. “Syndecan affects odor response as well as learning and memory in Drosophila melanogaster.”  American Journal of Undergraduate Research 15(1): 23-32, 2018.

    With M. Nguyen, J., Kwong, J. Chang, V.G. Gillet, R.M. Lee. “The Extracellular and Cytoplasmic domains of Syndecan cooperate postsynaptically to promote synapse growth at the Drosophilaneuromuscular junction.” PLOS One 11(3):e0151621, 2016.

    With E. Özkan, R.A. Carrillo, C.L. Eastman, R. Weiszmann, D. Waghray, K. Zinn, S.E. Celniker, K.C. Garcia. “An Extracellular Interactome of Immunoglobulin and LRR Proteins Reveals Receptor-Ligand Networks.” Cell 154(1):228-239, 2013.

    With I. Vilinsky. “Electroretinograms in Drosophila: A robust and genetically accessible electrophysiological system for the undergraduate laboratory.”  Journal of Undergraduate Neuroscience Education 11(1); A149-157, . 2012.

    With A.D. Smart, M.M. Course, J. Rawson, S. Selleck, D. Van Vactor. Heparan sulfate proteoglycan specificity during axon pathway formation in the Drosophila embryo. Developmental Neurobiology 71(7):608-618, 2011

    With A.P. Wright, A.N. Fox, and K. Zinn. "Systematic screening of Drosophila deficiency mutations for embryonic phenotypes and orphan receptor ligands. PLoS ONE 5(8): e12288, 2010

    With E. Stryker ('07), "LAR, liprin-alpha and the regulation of active zone morphogenesis, " Journal of Cell Science, 120: 3723-3728, 2007

    With A.P. Tenney, A. Duckworth, K. Parfitt, O. Marcu, T. Heslip, J. L. Marsh, J.G. Flanagan and D. Van Vactor, "The HSPGs Syndecan and Dallylike bind the receptor phosphatase LAR and exert opposing effects on synapse growth," Neuron, 49(4): 517-531, 2006

    With D. Van Vactor and D.P. Wahl, "Heparan Sulfate Proteoglycans and the emergence of neuronal connectivity, " Curr. Op. Neurobiology, 16(1): 40-51, 2006

    With J.M. Rawson, B. Dimitroff, X. Ge, D. Van Vactor and S. B. Selleck, "The heparan sulfate proteoglycans Dallylike and Syndecan have distinct functions in axon guidance and visual system assembly in Drosophila," Current Biology, Vol. 15:833-838, May 10, 2005

    With A. Ghose, E. Epstein, J. Lincecum, M. B. O'Connor and D. Van Vactor, "Axonal heparan sulfate proteoglycans regulate the distribution and efficiency of the repellent Slit during midline axon guidance," Current Biology, 14:499-504, 2004

  • Education


    Cambridge University

    Master of Science
    University of California, San Diego

    Bachelor of Art
    Grinnell College

    Professional Experience

    Postdoctoral Fellow

    Harvard Medical School

    Recent Courses Taught

    • Ind Std: Biology
    • Intro Cell Chem & Cell Bio w/Lab
    • Lab, Intro Cell Chem & Cell Biol
    • Lab, Vertebrate Sensory Systems
    • Vertebrate Sensory Systems
  • Awards & Honors

    Awards & Honors

    National Science Foundation, Research at Undergraduate Institutions. Division of Integrative Organismal Systems – Neural Systems Cluster. “Investigating the mechanisms of Syndecan function during nervous system development” $519,925 9/2009-8/2013

    National Institutes of Health, Academic Research Enhancement Award (AREA), three-year $216,556 grant for the project "Characterizing the function of Syndecan during CNS [central nervous system] development," 2008 (Declined)

    Wig Distinguished Professorship Award for Excellence in Teaching, 2008 & 2014

    National Science Foundation and Davidson College, $10,000 SOMAS grant, designed to support the research of new neuroscience faculty and their students at predominantly undergraduate institutions, 2008

    Helen Hay Whitney Postdoctoral Fellow, 2002-2005

    Cambridge Overseas Research Studentship, 1997-2000

    Phi Beta Kappa, member, 1995-present