Adaptive plasticity ofXenopus glial cells in vitro and after CNS fiber tract lesions in vivo

Abstract

Xenopus oligodendrocytes and aspects of their differentiation were analyzed in vitro and in vivo using cell-and stage-specific antibodies. Undifferentiated oligodendrocytes were derived from optic nerves or spinal cords. They divided in vitro, were of elongated shape, were glial fibrillary acidic protein and 0 4 positive, transiently exhibited several antigens including HNK-1 and L1, and promoted axon growth as do Schwann cells. With forskolin they differentiated and, much like myelin-forming oligodendrocytes in the intact optic nerve and spinal cord, they expressed sets of advanced myelin markers. These advanced myelin markers disappeared from the regenerating optic nerve 4 weeks after lesion. The optic nerve instead was populated by cells with radial processes and somata in the center of the nerve; among them were cells and processes that were 0 4 positive and that are suspected to represent undifferentiated oligodendrocytes. Where processes of these cells reached to the retinal axons in the nerve's periphery, advanced myelin markers typical of differentiated oligodendrocytes reappeared 8 weeks after lesion. These glial changes did not occur in the absence of retinal axons. Thus, the apparent capability of Xenopus oligodendrocytes to adapt to the transient absence, reappearance, and regenerative state of the axons enables them to contribute to central nervous system fiber tract repair. This occurs in the lesioned optic nerve but not in the spinal cord, where no such glial changes were observed and where axons fail to regenerate.

E587 antigen is upregulated by goldfish oligodendrocytes after optic nerve lesion and supports retinal axon regeneration

“…They properly remyelinate regenerated RGC axons in vivo (Wolburg, 1981) and thus contribute to the repair of lesioned CNS fiber tracts as Schwann cells do in the mammalian peripheral nervous system (reviewed in Fawcett and Keynes, 1990). This ''adaptive plasticity'' of Schwann cells and goldfish oligodendrocytes correlates with and may be causally linked to successful axon regeneration and the functional restoration of fiber tracts (Lang and Stuermer, 1996) which occurs in the PNS of mammals, and in both the PNS and CNS of fish.…”

“…Oligodendrocytes in fish apparently possess a degree of plasticity comparable to that seen in the amphibian visual system (Lang and Stuermer, 1996). They resemble Schwann cells in that they dedifferentiate and proliferate in vitro and respond to deprivation of axons by synthesizing cell adhesion proteins as well as growth factors.…”

Identification of two nogo/rtn4 genes and analysis of Nogo-A expression in Xenopus laevis

“…In frogs, CNS axons fail to regenerate in the spinal cord after metamorphosis (Beattie et al, 1990;Forehand and Farel, 1982). The inability of regeneration correlates with the nonpermissive properties of spinal cord myelin and oligodendrocytes in cocultures with axons, indicating the expression of inhibitory proteins in this region (Lang and Stuermer, 1996;Lang et al, 1995). CNS myelin and oligoden drocytes from the optic nerve and tectum, where amphibian axons do regenerate, were not inhibitory to growing axons in vitro (Lang et al, 1995).…”

Spinal cord regeneration: Lessons for mammals from non‐mammalian vertebrates

“…However, at postmetamorphic stages, some studies show scar formation at the lesion site, which is associated with a growth-inhibiting environment (Beattie et al, 1990;Lang et al, 1995). The distribution of oligodendrocytes, fibronectin, and GFAP positive cells in the injured spinal cord is consistent with the failure of axons to regrow (Lang and Stuermer, 1996).…”