Retinoic acid induces changes in the rhombencephalic neural crest cells migration and extracellular matrix composition in chick embryos

Chick embryos at 9-10 stages (Hamburger and Hamilton: J Morphol 88:49-82, 1951) have been treated with all-trans retinoid acid (RA) (0.5 microgram, 1.5 micrograms, and 2.5 micrograms) to determine the pattern and mechanism of RA-induced effects on early cephalic development. We found that while 0.5 microgram RA did not produce any significant dysmorphogenesis, 2.5 micrograms RA elicited wide malformation of both cephalic and trunk regions. However, 1.5 micrograms RA produced selective and specific changes at the cephalic level, which consisted of morphological alterations, changes in neural crest cells (NCC) migration and extracellular matrix (ECM) composition. Morphological alterations included hypoplasia of the first three branchial arches, swelling of either anterior cardinal veins or dorsal aortae, and atrophy of branchial arch arteries. Concurrently NCC did not migrate away, remaining clustered on the dorsal surface of the rhombencephalon, and in some cases they shifted into the neural tube cavity. Accordingly, the second branchial arch showed a reduction of the mesenchymal cellular population. The extracellular matrix in RA-injected embryos showed changes in glycosaminoglycans (GAGs) concentration as compared with controls, that is, an increase in the non-sulphated GAGs, stained with alcian blue 8GX at 2.5 pH, and a decrease in the sulphated GAGs stained with alcian blue 8GX at 1 pH. These quantitative changes reflected alterations in the pattern of distribution and composition of the GAGs within the cephalic ECM, which specifically consisted in an increase of the hyaluronic acid and a decrease of the chondroitin sulphate. Our findings indicate that RA is involved in abnormal cephalic development, suggesting that RA may effect neural crest cell migration via changes in the GAGs of the ECM.