Specific configurations of fibronectin‐containing particles correlate with pathways taken by neural crest cells at two axial levels

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Abstract
Although neural crest (NC) cells can potentially enter a number of intertissue spaces, they select a particular pathway that varies depending on the axial level. In the cranial region, NC cells enter the dorsal‐lateral pathway (i.e., immediately subjacent to the ectoderm) and avoid the ventral pathway (i.e., pathway between the mesoderm and neural tube and within the mesodermal cell population), whereas in the trunk region, the majority of the NC cells enter the ventral pathway (i.e., between the somite and neural tube) and not the dorsal‐lateral pathway. Our working hypothesis is that one determining factor in directing NC cell migration is the composition and/or intermolecular associations of the extracellular matrix (ECM) in these pathways. Histochemical staining, immunostaining, and lectin‐binding studies on cryofixed and conventionally fixed tissue were conducted to initially characterize the ECM found in potential NC cell pathways prior to and during initial NC cell migration at two different axial levels. We found that, regardless of the axial level, the pathways into which NC cells eventually enter possessed a characteristic ECM arrangement. This arrangement included: (1) the presence of multicomponent, glycoprotein‐containing spherical particles (0.1–0.5 μm in diameter); and (2) a low‐sulfated ECM content. Although all particles contained fibronectin, only those in specific regions were able to bind to a monoclonal antibody directed to the cell‐binding domain of fibronectin, suggesting that the conformation of fibronectin may be important in the expression of any in situ function of the molecule.