The role of ependyma in regeneration of the spinal cord in the urodele amphibian tail

Abstract

The new spinal cord formed during tail regeneration in the newt first develops as a caudal extension of the ependymal tube. Neuroblasts and neuroglia subsequently differentiate from cells of the ependymal tube in a proximal-caudal sweep. Descending axons from the cord rostral to the lesion and from newly differentiating neurons travel in channels which are present prior to the ingrowth of axons. The present study confirms previous observations from our laboratory and presents details of the ultrastructural relations of axons and ependymal processes within the cord. The ependymal cell surface facing channels typically forms numerous digitor sheet-like protuberances which extend into the channel lumen. As axons enter the channels in increasing numbers these protuberances partially subdivide the axons into smaller groupings, even occasionally segregating individual axons. At levels where fibers have not yet entered or have most recently entered the ependymal channesl two specializations appear on the ependymal plasmalemma facing the channels and their axons: coated membranes and hemidesmosome-like structures. At more mature levels, where many fibers have already entered the channels, axons in contact with ependymal processes sometimes show synapse-lide vesicle accumulations with associated membrane densities. Coated membranes and hemidesmosome-like structures are lacking at these levels. Our observations suggest that ependymal processes, in addition to providing substrate and direction for regenerating spinal cord axons, may also furnish or exchange more specific information at the morphologically identifiable specializations described above.

Cellular response after crush injury in adult zebrafish spinal cord

“…Initiation of proliferation starts at the site of injury as well as away from the stump and later proliferating cells migrate towards injury epicenter. Previous work in urodele spinal cord mentioned that the proliferation involves ependymal tissue somewhat distant to the plane of amputation (Egar and Singer, 1972;Nordlander and Singer 1978;Zhang et al, 2000) and that there was the presence of migrating proliferating precursors . We confirm injuryinduced proliferative response as observed by others (Egar and Singer, 1972;Nordlander and Singer, 1978;Zhang et al, 2000;Monaghan et al, 2007) and proliferation as a key event in initiation and maintenance of regenerative response in zebrafish spinal cord.…”

Neural crest‐like cells originate from the spinal cord during tail regeneration in adult amphibian urodeles

“…8) using the thymidine analogue bromodeoxyuridine (BrdU) to label cells in the DNA synthesis (Sphase) stage of cell division. The ependymal tube then differentiates, including the generation of glia and neurons that become organized to form a SC with a new normal and functional structure (Butler and Ward, 1967;Egar and Singer, 1972;Iten and Bryant, 1976;Nordlander and Singer, 1978;Singer et al, 1979;Mutin-Martin, 1990;Arsanto et al, 1992).…”

Monoclonal antibody R2D5 reveals midsagittal radial glial system in postnatally developing and adult brainstem.

“…These are the first class of glial cells to appear during embryonic development and they are thought to play critical roles in organizing the spatial arrangement of the nervous system (1,2). In lower vertebrates, for example, radial processes of ependymal cells have been reported to form channels for growing axons during both regeneration and embryonic development and thus have been suggested to display on their surfaces trace pathways that the axons follow toward their destination (3,4). In the mammalian embryo, ependymal cells project their processes (radial glial fibers) to almost all regions of the brain and are thought to supply pathways guiding the migration of newly generated neurons (1,5).…”