Soonmoon Yoo, Ph.D.

Research Interests

Axons damage to the central nervous system (CNS) including brain and spinal cord do not spontaneously regenerate and there are currently no effective treatments, resulting in irreversible and permanent neurophysiological dysfunction. Each year, it is estimated that more than 2 million people in the United States alone sustain traumatic brain injuries and approximately 12,000 new cases are annually added to an estimated 400,000 patients with spinal cord injuries. By contrast, axonal injury to the peripheral nervous system (PNS) normally shows a robust regenerative response. These spontaneous regenerative responses of peripheral nerves can be experimentally further enhanced by a pre-conditioning injury to the nerve, for which the peripheral nerve has been given an injury prior to being subjected to another injury. De novo protein synthesis is a key component of this enhanced regeneration.  Although most proteins are synthesized in the cell body, our previous study has shown that many mRNAs are differentially localized into axons of neurons to accomplish local and autonomous de novo protein synthesis. Translation of mRNAs directly in the axonal compartment is now known to contribute to axonal growth and regeneration.  Studies on axonal mRNAs will provide invaluable insight into the molecular changes that occur in the regenerating nerve.  The long-term goal of our laboratory is to uncover the molecular mechanisms that regulate de novo protein synthesis needed to regenerate axons.  Determination of mechanisms that lead to regeneration of peripheral nerves will enable development of new strategies to promote axonal regrowth within the CNS.

Biological functions of RNA localization and local protein synthesis in regenerating axons

Neurons are large polarized cells that provide the long-range communication in the nervous system underlying nearly every function of the brain and spinal cord.  mRNA localization into and localized translation within the long processes of neurons provide a means for rapid and autonomous responses to stimuli at distances 10 to 1000 fold more than the cell body diameter. For example, protein synthesis in the post-synaptic compartment (i.e., dendritic spines) leads to persistent changes in synaptic connectivity and efficacy, functions that are thought to underlie learning and memory. Protein synthesis in axons of developing neurons is needed for response to guidance cues (i.e., pathfinding) that determines how the developing nervous system is wired.  In contrast, mature vertebrate axons appear to have limited capacity for local protein synthesis.  However, axonal injury to adult nerves triggers localized synthesis of new proteins and these new proteins are needed for the retrograde signaling that underlies the cell body's response to injury. Thus, despite that mature axons seem to have limited translational machinery, axonal injury is able to recruit this machinery to synthesize new proteins that are needed for regeneration, including proteins needed for growth cone formation.  Our previous studies have also shown that this axonal protein synthesis is quite robust during the process of regeneration and is needed to maintain the structure of the distal axon. The pith of the concurrent research is to know the exact cellular/molecular mechanisms that result in different responses to injury between the CNS and PNS neurons to cure currently incurable neurological diseases.  This information will allow us to manipulate the properties and eventually to prevent or, at least, lessen loss of function resulting from injury to the central nervous system, e.g., paralysis after spinal cord injury, and finally to promote the recovery. 

Spatiotemporal regulation of local protein synthesis in regenerating axons

Successful axon regeneration is likely to be accomplished through a sophisticated coordination of gene expression at both transcriptional and post-transcriptional levels, i.e., newly synthesized proteins through changes of gene expression in the cell body and local translation at the injury site, respectively. However, to date, there is no study that has rigorously investigated how such gene-specific regulation in subcellular domains occurs. Understanding of molecular and cellular mechanisms underlying coordinated regulation of local protein synthesis during regeneration will be required for appreciating the pathophysiological complexity and for developing future therapeutic agents in nerve regeneration of CNS/PNS neurons.

Small non-coding RNAs, including microRNAs (miRNA), have recently been recognized as a prominent player in post-transcriptional regulation of local protein synthesis. What makes miRNAs very interesting, as gene-specific regulators in nervous system, is their enormous diversities in heterogeneity and function.  Since the first discovery of the existence of miRNA lin-4 miRNA and its regulatory role in cell fate determination of the C. elegans larvae in 1993, 2042 miRNAs have been identified in humans and deposited in database (miRBase, Release of 19, http://www.mirbase.org) and the number is continuously growing.  Of those, almost 50% are differentially distributed in distinct subareas of the brain as well as in subcellular domains of neurons and are predicted to control ~ 30% of all protein coding genes.  Enormously different miRNAs expressed in neurons provide means to simultaneously control many different gene- specific translations.  miRNAs also enable many different synapsing axons and dendritic spines on the same neuron to behave differentially in response to extracellular stimuli, suggesting a fine-tuning of gene expression, rather than a simple on-off expression switch.  In addition, a specific miRNA can have hundreds of target mRNAs, but several different miRNAs can also share the same target transcript.  These suggest that miRNAs are capable to simultaneously regulate multiple genes in response to one or multiple extracellular cues.  The extreme complexity in miRNA-dependent regulation of axonal gene expression could provide an effective way to ensure the tight and precise control of neuronal gene expression required for regenerative program that is reactivated upon injury to axon. Although it is now certain that the miRNAs localize into axons and play a role in the coordinated regulation of local protein synthesis in regenerating axons, how these non-coding RNAs translocate into distal process of neurons is completely unknown to date. Interestingly, several recent studies show the presence of Dicer and components of the miRNA-induced silencing complex (miRISC) that are required for processing precursor miRNAs (pre-miRNAs) to mature functional miRNAs both in dendrites and axons. Processing of a pre-miRNA to mature miRNA locally in neuronal processes could confer a unique advantage for coordinately altering the population of proteins generated in growth cones by targeting mRNA cohorts. Therefore, we hypothesize that specificity of axonally transported pre-miRNAs confers spatiotemporal regulation of local protein synthesis in regenerating axons. Understanding molecular mechanisms of miRNA localization as well as local miRNA biogenesis in neurons will provides the basis for future research of gene expression regulation to promote functional recovery following CNS injury.

Current Projects

  • Identification of axonally localized mRNAs encoding for injury-response and growth-associated proteins that are necessary for nerve regeneration

  • Characterization of molecular determinant(s) of axonal mRNAs requisite for axonal regeneration.

  • Identification of trans-acting factors that are needed for mRNA localization and translation of axonal mRNAs.

  • Determination of the function of trans-acting factor(s) for axonal mRNAs of injury-response and growth-associated proteins.

  • Characterization of signaling pathways that are involved in regulation of local protein synthesis in regenerating axons.

  • Identification of axonally localizing precursor miRNAs in regenerating axons.

  • Characterization of precursor miRNA localization.

  • Examination of roles of miRNAs that are maturated from localized precursor miRNAs in regenerating axons.

Research Group

  • Soonmoon Yoo, Ph.D. – Principal investigator

  • Hak Hee Kim, Ph.D. – Postdoctoral fellow

  • Paul Kim, B.S. – Research Assistant II

Selected Publications

  • Yoo, S., Kim, H.H., Kim, P., Donnelly, C.J., Kalinski, A.L, Vuppalanchi, D., Park, M., Lee, S.J., Merianda, T.T., Perrone-Bizzozero, N.I., Twiss, J.L. 2013. A HuD-ZBP1 ribonucleoprotein complex localizes GAP-43 mRNA into axons through its 3’ untranslated region AU-rich regulatory element. J. Neurochem. In press.
  • Donnelly, C.J., Park, M., Spillane, M., Yoo, S., Pacheco, A., Gomes, C., Kim, H.H., Merianda, T.T., Gallo, G., Twiss, J.L. 2012.  Axonally synthesized b-actin and GAP-43 proteins support distinct modes of axonal growth. J. Neurosci. 33:3311-22.
  • Merianda, T.T., Vuppalanchi, D., Yoo, S., Blesch, A., Twiss, JL. 2012. Axonal transport of neural membrane protein 35 mRNA increases axon growth. J. Cell Sci. Epub ahead of print.
  • Vuppalanchi, D., Merianda, T.T., Donnelly, C.J., Williams, G., Yoo, S., Ratan, R.R., Willis, D.E., Twiss, J.L. 2012. Lysophosphatidic acid differentially regulates axonal mRNA translation through 5’UTR elements. Mol. Cell Bio. 50:136-46.
  • Yoo, S., Twiss, JL. 2011. The road not taken: new destinations for yeast mRNAs on the move. EMBO J. 30:3564-6.
  • Donnelly, C.J., Willis, D.E., Xu, M., Tep, C., Jiang, C., Yoo, S., Schanen, N.C., Kirn-Safran, C.B., van Minnen, J., English, A., Yoon, S.O., Bassell, G.J., Twiss, J.L. 2011.  Limited availability of ZBP1 restricts axonal mRNA localization and nerve regeneration capacity. EMBO J. 30:4665-77.
  • Barrientos, S.A., Martinez, N.W., Yoo, S., Jara, J.S., Zamorano, S., Hetz, C., Twiss, J.L., Alvarez, J., Court, F.A. 2011.  Axonal degeneration is mediated by the mitochondrial permeability transition pore. J. Neurosci. 31:966-978.
  • Vuppalanchi, D., Coleman, J., Yoo, S., Merianda, T.T., Yadhati, A.G., Hossain, J., Blesch, A., Willis, D.E., Twiss, J.L. 2010.  Conserved 3’UTR sequences direct subcellular localization of chaperone protein mRNAs in neurons. J. Biol. Chem.285:18025-38.
  • Yoo, S., * van Niekerk, E.A., Merianda, T.T., Twiss, J.L. 2010.  Dynamics of axonal mRNA transport and implications for peripheral nerve regeneration. Exp. Neurol. 223:19-27, PMCID: PMC2849851. (* S. Yoo and E.A. van Niekerk contributed equally to this work).
  • Wu, J., * Yoo, S., Wilcock. D., Lytle, J.M., Leung, P.Y., Colton, C.A., Wrathall, J.R. 2010.  Interaction of NG2+ glial progenitors and microglia/macrophages from the injured spinal cord. Glia. 58:410-422. PMCID: PMC2807472 (* J. Wu and S. Yoo contributed equally to this work).
  • Yudin, D., Hanz, S., Yoo, S., Lavnilovitch, E., Willis, D., Gradus, T., Segal-Ruder, Y., Ben-Yaakov, K., Hieda, M., Yoneda, Y., Twiss, J.L., Fainzilber, M.  2008.  Localized regulation of axonal RanGTPase controls retrograde injury signaling in peripheral nerve. Neuron 59:241-252.
  • Yoo, S., Wrathall, J.R. 2007.  Mixed primary culture and clonal analysis provide evidence that NG2 proteoglycan-expressing cells after spinal cord injury are glial progenitors. Dev. Neurobiol. 67:860-874.
  • Zai, L.J., Yoo, S., Wrathall, J.R. 2005.  Increased growth factor expression and cell proliferation after contusive spinal cord injury. Brain Res. 1052:147-155.
  • Wu, X.F., Yoo, S., Wrathall, J.R. 2005. Real-time PCR analysis of temporal-spatial alterations in gene expression after spinal cord contusion. J. Neurochem. 93:943-952.
  • Yoo, S., Wrathall, J.R. 2004.  (Cover image - Oligodendrocyte cells in primary culture). Nature Medicine, 10(6) June 2004.
  • Yoo, S., Bottenstein, J.E., Bittner, G.D., and Fishman, H.M. 2004. Survival of Mammalian B104 Cells following Neurite Transection at Different Locations Depends on Somal Ca2+ Concentration. J. Neurobiol. 60:137-153.
  • Yoo, S., Nguyen, M.P., Fukuda, M., Bittner, G.D., Fishman, H.M. 2003. Plasmalemmal Sealing of Transected Mammalian Neurites is a Gradual Process Mediated by Ca2+-regulated Proteins. J. Neurosci. Res. 74:541-551.
  • Detrait, E.R., Eddleman, C.S., Yoo, S., Fukuda, M., Nguyen, M.P., Bittner, G.D., Fishman, H.M. 2000. Axonal repair requires proteins that mediate synaptic vesicle fusion. J. Neurobiol. 44:382-391.
  • Detrait, E.R., Yoo, S., Eddleman, C.S., Fukuda, M., Bittner, G.D., Fishman, H.M. 2000. Plasmalemmal repair of severed neurites of PC12 cells requires Ca2+ and synaptotamin. J. Neurosci. Res. 62: 566-573.

Affiliated Scientist, Department of Biological Sciences

Phone: (302) 298-7006

Fax: 302-651-6767

Email: yoo@medsci.udel.edu

Office: Nemours Biomedical Research

Address:
Alfred I. DuPont Hospital for Children
1701 Rockland Road
Wilmington, DE 19803