The development of the head and neck, as well as the embryo in general, is the result of sophisticated cellular migrations which form virtually all of the skeletal, muscular and glandular structures. The mechanisms that underlie the initiation, directionally and cessation of cell migrations are poorly understood, despite the fact that they are responsible for some of the most common congenital malformations. During the past few years, my laboratory has identified a novel molecular mechanism for mesenchymal cell interactions with the underlying basal lamina matrix. Results show that cell surface galactosyltransferease (GalTase) participates during cell spreading and migration on basal lamina by binding to specific N-linked oligosaccharides primarily on the 400kDa subunit of laminin. Cell spreading and migration can be either inhibited or stimulated by reagents that selectively inhibit or stimulate surface GalTase activity. GalTase does not participate during the initial adhesion to laminin, which is mediated by a distinct laminin receptor(s). GalTase is localized by indirect immunofluorescence to cell lamellipodia and filopodia, consistent with its proposed role during spreading and migration. GalTase does not participate during cell spreading and migration on fibronectin, which relies upon totally independent mechanisms. During the next funding period we will: 1) identify the precise oligosaccharide chain in laminin that binds GalTase using HPLC and NMR analyses, 2) define the mechanisms that polarize GalTase to cell lamellipodia leading to directional cell migrations, 3) study the mechanisms that release GalTase from the substrate and/or cell surface enabling the cell to continue migrating, 4) determine whether GalTase participates during neurite outgrowth on laminin as it does during filopodial formation, and 5) address the role of surface GalTase during embryonic development in vivo by microinjecting reagents that perturb GalTase activity into the pathway of migrating cells. All of these studies will utilize a multidisciplinary approach including biochemical, immunological and molecular genetic probes.
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