Journal of Neuroscience, Vol 8, 653-663, Copyright © 1988 by Society for Neuroscience
Schwann cell surfaces but not extracellular matrix organized by Schwann cells support neurite outgrowth from embryonic rat retina
N Kleitman, P Wood, MI Johnson and RP Bunge
Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110.
Despite evidence that glial cell surfaces and components of the
extracellular matrix (ECM) support neurite outgrowth in many culture
systems, the relative contributions of these factors have rarely been
compared directly. Specifically, it remains to be determined which
components of peripheral nerve support growth of central nerve fibers. We
have directly compared neurite outgrowth from embryonic day 15 rat retinal
explants placed onto beds of (1) Schwann cells without ECM, (2) Schwann
cells expressing ECM (including a basal lamina), (3) cell-free ECM prepared
from neuron-Schwann cell cultures, (4) nonglial cells (fibroblasts), and
(5) 2 isolated ECM components, laminin and type I collagen. From the first
day in culture, retinal explants extended neurites when placed on Schwann
cells without ECM. Outgrowth on Schwann cells expressing ECM was also
extensive, but not obviously different form that on Schwann cells alone.
Ultrastructural study revealed that 95% of retinal neurites in
ECM-containing cultures contacted other neurites and Schwann cell surfaces
exclusively. On cell-free ECM prepared from neuron-Schwann cell cultures,
neurite extension was poor to nonexistent. No neurite outgrowth occurred on
fibroblasts. Retinal explants also failed to extend neurites onto purified
laminin and ammoniated type I collagen substrata; however, growth was rapid
and extensive on air-dried type I collagen. In cultures containing islands
of air-dried type I collagen on a laminin-coated coverslip, retinal
explants attached and extended neurites on collagen, but these neurites did
not extend off the island onto the laminin substratum. We conclude from
these experiments that neurite extension from embryonic rat retina is
supported by a factor found on the surface of Schwann cells and that
neither organized nor isolated ECM components provide this neurite
promotion. These findings are discussed in relation to possible species
differences in growth requirements for retinal ganglion cell neurites and
to the specificity of response of different CNS neurites to ECM substrata.