CELL-ADHESION MOLECULES REGULATE GUIDANCE OF DORSAL-ROOT GANGLION AXONS IN THE MARGINAL ZONE AND THEIR INVASION INTO THE MANTLE LAYER OF EMBRYONIC SPINAL-CORD
T. Shiga et al., CELL-ADHESION MOLECULES REGULATE GUIDANCE OF DORSAL-ROOT GANGLION AXONS IN THE MARGINAL ZONE AND THEIR INVASION INTO THE MANTLE LAYER OF EMBRYONIC SPINAL-CORD, Developmental biology, 192(1), 1997, pp. 136-148
In order to elucidate the mechanisms regulating the projections of dor
sal root ganglion (DRG) axons in the dorsal funiculus and invasion int
o target regions in the mantle layer (prospective gray matter) of the
spinal cord, we examined the interactions between DRG axons and spinal
cord. DRG neurons were dissociated from chick embryos and cultured fo
r 1-2 days on cryostat sections of the spinal cord at embryonic day 5
(E5) or at E9. E5 and E9 DRG neurons extended neurites onto both margi
nal zone (prospective white matter) and mantle layer (prospective gray
matter) of the spinal cord, suggesting that both of these regions are
permissive for neurite growth. When E5 DRG neurites approached cryose
ctions of E5 spinal cord from outside, most of them ran in the margina
l zone without invading the mantle layer. In contrast, about half of E
9 DRG neurites entered the mantle layer after crossing the marginal zo
ne of E9 spinal cord. These growth patterns of DRG neurites on spinal
marginal zone and mantle layer are similar to the pathway formation of
DRG axons at comparable stages in vivo; DRG axons run exclusively in
the prospective dorsal funiculus before E6, and enter the mantle layer
(prospective dorsal horn) to reach the target regions by E9. Perturba
tion of functions of Ng-CAM, Nr-CAM, and axonin-1/SC2 by adding the sp
ecific antibodies in the culture medium increased the ratio of DRG neu
rites entering the mantle layer of E5 spinal cord, suggesting that the
se cell adhesion molecules are involved in keeping DRG neurites in the
marginal zone. Taken together with the expression of Ng-CAM, Nr-CAM,
and axonin-1/SC2, these CAMs on DRG axons may regulate the guidance of
these axons in the marginal zone before E6, and the subsequent decrea
se in the relative levels of these CAMs might allow DRG axons to invad
e the target mantle layer. (C) 1997 Academic Press.