Rostrocaudal differences in the expression of extracellular matrix proteins by avian neural crest cells in vitro

Cranial and trunk neural crest cells developing in vitro differed in their patterns of expression of two major extracellular matrix proteins, fibronectin and collagen I. Cranial neural crest cells showed two distinct phases of fibronectin expression: the first occurred during the initial migration of cells from explants onto the culture dish; the second was associated with the differentiative period of in vitro development. Fibronectin-immunoreactive cells eventually represented one of the most abundant cell types in cranial cultures. Large numbers of procollagen I-immunoreactive cells also developed in cranial cultures, and procollagen I was colocalized with fibronectin in individual cranial neural crest cells. Neither fibronectin nor procollagen I immunoreactivities were seen in either neurons or melanocytes, consistent with the idea that the fibronectin-immunoreactive cells in cranial neural crest cultures are committed to the mesenchymal lineage. In contrast to cranial neural crest, trunk neural crest produced very few fibronectin-immunoreactive cells at any time in vitro. Trunk neutral crest also produced smaller proportions of procollagen I-immunoreactive cells than did cranial explants. Mitotic labelling experiments showed that the differing proportions of fibronectin- and procollagen I-immunoreactive cells in cranial versus trunk cultures did not result from differences in rates of cell proliferation.