Abstract:
Retinoic acid, the active metabolite of Vitamin A is known to play a major role in
embryonic growth and differentiation during development. It has been shown that either
excess or deficiency of retinoic acid during embryogenesis can be teratogenic. In order to
study the teratogenic effects of retinoic acid, the aim of the present study was therefore to
investigate the effect of all-trans retinoic acid on the migration and fate of neural crest
cells in vitro and in vivo. In addition, the study investigated the effect of retinoic acid on
the cytoskeletal elements of neural crest cells and on Rac and Rho, two members of the
Rho family of GTPases. The neural tubes containing neural crest cells of quail embryos
were removed at cranial levels and cultured on fibronectin as a substrate. The neural
tubes were cultured in either Dulbecco’s minimal essential medium (DMEM) or in
DMEM+Dimethylsulphoxide (DMSO) as controls. In order to test the effect of retinoic
acid, the neural tubes were cultured in 10-5M all-trans retinoic acid (RA) which was
reconstituted in DMSO. The distance of migration of the cultured quail neural crest cells
was measured and compared between the controls and the experimentals. To study the
effect of RA on the cell actin cytoskeleton in vitro, cultured neural crest cells were
stained with rhodamine phalloidin. In addition, following 24 hours of culture, the quail
neural crest cells were brought into suspension and micro-injected into 36 hour-old chick
hosts. While the migration of neural crest cells was extensive in the control cultures in
vitro, migration was inhibited in the retinoic acid-treated neural crest cells. In addition,
retinoic-acid treated neural crest cells showed pigmentation and neuronal processes
earlier than did the control neural crest cells. Retinoic acid-treated neural crest cells
showed a disarray of the cytoskeletal elements as they were devoid of stress fibres and
focal adhesions. In addition, retinoic acid appears to decrease the expression of Rac and
Rho of cultured quail neural crest cells. Following micro-injection of cultured control and
RA-treated quail neural crest into the cranial region of chick hosts, the control cells
populated the beak area, whereas the retinoic acid-treated quail neural crest cells
migrated to the retina of the eye, a region they normally do not populate. These results
suggest that retinoic acid disturbs the migration of neural crest cells. It appears to do this
by affecting the cytoskeletal elements of neural crest cells and the genes that are involved
in forming these elements.
