ɑ_1β_1 integrin on neural crest cells recognizes some laminin substrata in a Ca^(2+)-independent manner

Neural crest cells migrate along pathways containing laminin and other extracellular matrix molecules. In the present study, we functionally and biochemically identify an ɑ_1β_1 integrin heterodimer which bears the HNK-1 epitope on neural crest cells. Using a quantitative cell adhesion assay, we find that this heterodimer mediates attachment to laminin substrata prepared in the presence of Ca^(2+). Interestingly, neural crest cells bind to laminin-Ca^(2+) substrata in the presence or absence of divalent cations in the cell attachment medium. In contrast, the attachment of neural crest cells to laminin substrata prepared in the presence of EDTA, heparin, Mg^(2+), or Mn^(2+) requires divalent cations. Interactions with these laminin substrata are mediated by a different integrin heterodimer, since antibodies against β_1 but not ɑ_1 integrins inhibit neural crest cell attachment. Thus, the type of laminin substratum appears to dictate the choice of laminin receptor used by neural crest cells. The laminin conformation is determined by the ratio of laminin to Ca^(2+), though incorporation of heparin during substratum polymerization alters the conformation even in the presence of Ca^(2+). Once polymerized, the substratum appears stable, not being altered by soaking in either EDTA or divalent cations. Our findings demonstrate: (a) that the ɑ_1β_1 integrin can bind to some forms of laminin in the absence of soluble divalent cations; (b) that substratum preparation conditions alter the conformation of laminin such that plating laminin in the presence of Ca^(2+) and/or heparin modulates its configuration; and (c) that neural crest cells utilize different integrins to recognize different laminin conformations