Using Gene Knockout and Transgenic Approaches to Evaluate in vivo Functions of CNS Regeneration Inhibitors: How Important is Nogo?

Nerve cells of the central nervous system (CNS) are distinct from the peripheral nervous system (PNS) in that they are not capable of regenerating after injury (Purves, D. et al. 2001). In recent studies, scientists have discovered that the agents causing this inability to regenerate are myelin-derived protein inhibitors that form three families—MAG, OMgp, and Nogo with a common receptor, NgR (GrandPre, T. et al. 2000). Through alternative splicing and use of two promoters, the Nogo gene accounts for three proteins: Nogo-A, Nogo-B, and Nogo-C. Recent in vivo studies on Nogo-A (Simonene, M. et al. 2003) and Nogo-A/B mice (Kim, J. et al. 2003) have shown potential for regeneration of axons after injury. However, in the field of neuroregeneration, the Nogo controversy has led to a race to define exactly what role Nogo and other inhibitory molecules play. The controversy’s underlying basis is the fact that axonal regeneration in Nogo-A mice created by Martin E. Schwab’s lab (Simonene, M et al. 2003) is only modest, while axonal regeneration in NogoA/B mice created by Stephen M. Strittmatter’s lab (Kim, J. et al. 2003) is significant yet decreases upon age. In this proposal, we will develop a NogoB knockout from Schwab's Nogo-A mice to alleviate the discrepancies in levels of axonal regeneration seen in Schwab’s and Strittmatter’s mice. Next, we will address the issue of minimal axonal regeneration in the older mice (>11 weeks) from Strittmatter’s lab (Kim, M. et al. 2003). The functionality of MAG has been reported to have a minor role as a secondary inhibitor of axonal regeneration in vitro and in vivo. However, the effect of OMgp has not yet been studied in vivo, and we hypothesize that the minimal axonal regeneration seen in the older mice (>11 weeks) from Strittmatter’s lab is caused by OMgp expression in the older mice. We will first assess levels of OMgp expression in younger (6-11 weeks) and older (>11 weeks) wild type mice. We will also create knock out mice for OMgp and OMgp/NogoA/Nogo-B to test the extent of axonal regeneration. Finally, the effect of OMgp