The contribution of beta1 integrins to neuronal migration and differentiation depends on extracellular matrix molecules.

The interaction of beta1 integrin receptors and different extracellular matrix molecules during neuronal development was investigated by comparing both migration and morphological differentiation of D3 wild-type embryonic stem (ES) cell line-derived neural precursor cells with those of the beta1 integrin knockout ES cell line G201. Analysing neurosphere explants on laminin and fibronectin as major beta1 integrin ligands, the maximal spreading of outward migrating neuronal cells was determined. Compared with gelatine as a standard substrate, migration was found to be significantly increased for D3-derived neurospheres on fibronectin and laminin-1. These matrix effects were found to be even enhanced for G201 preparations. In addition, also the differentiation of wild-type and beta1 integrin -/- neurones - as determined by MAP-2- and HNK-1-immunoreactive processes - was found to be increased on fibronectin and laminin when compared to gelatine standards. In the respective knockout preparations on these matrices, again perturbation effects were less pronounced than on gelatine. Our observations indicate that laminin and fibronectin are involved both in beta1 integrin-dependent and -independent signalling mechanisms during neurogenesis. Upregulation of compensatory mechanisms such as beta1 integrin-independent receptors for laminin and fibronectin might be responsible for the much less pronounced perturbations of G201 neural precursor migration and differentiation on these two substrates than on gelatine.