Journal of Neuroscience, Vol 15, 7226-7237, Copyright © 1995 by Society for Neuroscience
Impaired peripheral nerve regeneration in a mutant strain of mice (Enr) with a Schwann cell defect
EM Rath, D Kelly, TW Bouldin and B Popko
Brain and Development Research Center, University of North Carolina, Chapel Hill 27599-7250, USA.
Schwann cell-axon interactions in the development, maintenance, and
regeneration of the normal peripheral nervous system are complex. A
previously described transgene-induced insertional mutation (BPFD#36), now
referred to as Enervated (Enr), results in disrupted Schwann cell- axon
interactions. In this report, after a crush or transection injury to Enr
peripheral nerves, we demonstrate impaired nerve regeneration. There are
fewer myelinated fibers per mm2 and thinner myelin sheaths surrounding
regenerating axons in the nerves of homozygous mutant mice compared to wild
type mice at 28 d after crush injury to the sciatic nerve. Abnormal Schwann
cell-axon interactions remain in Enr/Enr animals as evidenced by the
relatively frequent ultrastructural finding of unmyelinated large diameter
axons in the regenerating nerves. Additionally, nerve graft experiments
indicate that the impairment in regeneration is due to a Schwann cell
defect. Morphologic and morphometric findings in conjunction with molecular
analysis of regenerating nerves suggest that the Enr defect causes a
disruption in the ability of "early" Schwann cells to differentiate to a
more mature phenotype. In mutant homozygous and wild type nerves at 7 d
after crush injury there are similar levels of mRNA for the low-affinity
nerve growth factor receptor, but in the mutant homozygous regenerating
nerves there is 11-fold less mRNA for glial fibrillary acidic protein, a
more mature phenotypic marker of Schwann cells. This Schwann cell
differentiation defect likely accounts for both the peripheral neuropathy
and impaired nerve regeneration observed in Enr mice.