Generation of an OMgp allelic series in mice

Abstract

SummaryThe very limited ability to regenerate axons after injury in the mature mammalian central nervous system (CNS) has been partly attributed to the growth restrictive nature of CNS myelin. Oligodendrocyte myelin glycoprotein (OMgp) was identified as a major myelin-derived inhibitor of axon growth. However, its role in axon regeneration in vivo is poorly understood. Here we describe the generation and molecular characterization of an OMgp allelic series. With a single gene targeting event and Cre/FLP mediated recombination, we generated an OMgp null allele with a LacZ reporter, one without a reporter gene, and an OMgp conditional allele. This allelic series will aid in the study of OMgp in adult CNS axon regeneration using mouse models of spinal cord injury. The conditional allele will overcome developmental compensation when employed with an inducible Cre, and allows for the study of temporal and tissue/cell type-specific roles of OMgp in CNS injury-induced axonal plasticity. KeywordsOMgp; conditional allele; axon regeneration; CNS repair; myelin inhibition Following development, axons in the mammalian central nervous system (CNS, including the brain and the spinal cord) have largely lost the ability to regenerate in response to injuries (Ramón y Cajal, 1928). Spinal cord injury patients suffer permanent functional deficits due to this inability for axon regeneration in adult CNS, which is in contrast with the robust regenerative ability of axons in the developing CNS or in the adult peripheral nervous system (PNS). The inhibitory action of myelin on axon growth has been hypothesized as one primary reason for this loss of regenerative ability (Berry, 1982;Schwab and Bartholdi, 1996). Several myelin-derived inhibitory proteins have been identified (Filbin, 2003;Yiu and He, 2006). Oligodendrocyte Myelin glycoprotein (OMgp) was identified as a major myelin-derived inhibitor that possesses potent inhibitory activity on neurite outgrowth in vitro (Kottis et al., 2002;Wang et al., 2002). Together with two other myelin inhibitors, Nogo and myelin-associated glycoprotein (MAG), it signals through at least two receptors, NgR1 and PirB, to effect the inhibitory action of myelin (Atwal et al., 2008;Yiu and He, 2006). However, the role of OMgp in axon regeneration in vivo is not well understood. In a published report, OMgp deficient mice were found to exhibit slightly enhanced axon regeneration in the ascending dorsal column sensory tract and the descending raphespinal serotonergic tract but not in the corticospinal tract (Ji et al., 2008 Zheng et al., 2005). A MAG mutant exhibits upregulated NgR1 expression (Pernet et al., 2008). Thus, mutations in either an inhibitory ligand or receptor in the myelin inhibition pathway can lead to changes in the expression of other genes in the pathway, which may mask the effect of gene deletion (in the case of the NgR1 or MAG mutants) or complicates the interpretation of the results (in the case of the OMgp mutant). This is particularly a challenge for genetic studies of axon regener...

Assessing Spinal Axon Regeneration and Sprouting in Nogo-, MAG-, and OMgp-Deficient Mice

“…We have recently described the generation of a Nogo deletion mutant and an OMgp null mutant (Lee et al, 2009a; Lee et al, 2009b). The Nogo deletion mutant differs from all other Nogo mutants published in that it is the only Nogo null that is fully viable and lacks the expression of all known Nogo isoforms including Nogo-A,B,C, and thus would allow for unequivocal assessment of all Nogo isoforms (Lee et al, 2009b).…”

“…The Nogo deletion mutant differs from all other Nogo mutants published in that it is the only Nogo null that is fully viable and lacks the expression of all known Nogo isoforms including Nogo-A,B,C, and thus would allow for unequivocal assessment of all Nogo isoforms (Lee et al, 2009b). Given the unusual location of the OMgp gene in the intron of the Neurofibromin 1 gene ( NF1 ), we designed the OMgp mutation to minimize any effect on NF1 expression (Lee et al, 2009a). The Nogo and OMgp mutants were bred to a previously characterized MAG null mutant (Li et al, 1994) to obtain Nogo/MAG/OMgp triple null mutants in a mixed background with 129S7 and C57BL/6 (see supplemental Experimental Procedures), which proved viable, fertile and exhibited no gross morphological defects.…”

STAT3 and SOCS3 regulate NG2 cell proliferation and differentiation after contusive spinal cord injury

“…(intraperitoneal) with 0.124mg/g body weight of tamoxifen (MP Biomedicals) as previously described (Lee et al, 2009) for 5 consecutive days. One week after the last injection, mice were anesthetized (ketamine/xylazine, 100 mg/15 mg/kg i.p.)…”

Guidance Molecules in Axon Regeneration

“…OMgp is linked via a glycosylphosphatidylinositol (GPI) anchor to the cell surface and is expressed by myelinating glia in the CNS but not the PNS (Mikol and Stefansson, 1988). In addition, OMgp is strongly expressed by many types of neurons in the mature CNS (Habib et al 1998;Lee et al 2009a). Although OMgp null mice do not show detectably enhanced growth of axotomized corticospinal axons, increased sprouting of serotonergic axons has been reported (Ji et al 2008).…”