Distribution and synthesis of glycosaminoglycans during quail neural crest morphogenesis

Recent evidence has suggested that both localization and phenotypic expression of neural crest cells depend upon environmental cues encountered during migration. As an initial step in the description of this environment, glycosaminoglycans (GAG) in regions of trunk neural crest morphogenesis in quail embryos were characterized histochemically. Crest cells initially migrate into an Alcian blue-staining matrix that includes primarily hyaluronic acid, but also sulfated GAG. Later, crest cells that migrate between the ectoderm and somite (presumptive melanoblasts) remain surrounded by a matrix rich in GAG, compared to the extracellular matrix (ECM) surrounding crest cells which aggregate to form spinal ganglia. Autoradiography of sections of embryos incubated with [³H]glucosamine prior to fixation revealed that Streptomyces hyaluronidase-sensitive labeled material was present in the region occupied by neural crest cells during the initial stages of their migration. Thus, at least some of the hyaluronic acid demonstrated histochemically was synthesized at the time when crest cell migration was being initiated. To examine the possible contributions of different tissues to this matrix, separate in vitro cultures of 2-day quail embryo trunk neural crest and crest-free somite and ectoderm were established and incubated for 24 hr with labeled GAG precursors. GAG were isolated and then characterized by two different procedures: (1) two-dimensional cellulose acetate electrophoresis and (2) GAG degradation coupled with analysis on a Sephadex G-50 column. Results from both methods indicated that isolated crest cells incorprate [³H]glucosamine primarily into hyaluronic acid. Somite and ectoderm cells incorporate a significantly higher percentage of precursor into sulfated classes of GAG than do crest cells, although hyaluronic acid is also the predominant GAG synthesized by these cell types. These results suggest that crest cells contribute to their own environment in vivo and that the pattern of GAG synthesis varies among different cell types, which in turn affects the composition of ECM in adjacent embryonic tissue spaces.