EVIDENCE FOR CELL-SURFACE EXTRACELLULAR-MATRIX BINDING-PROTEINS IN HYDRA-VULGARIS

The present study was designed to identify and functionally characteri ze potential cell surface extracellular matrix binding proteins in Hyd ra vulgaris. Using [H-3]-laminin as a probe, radioreceptor analysis of a dissociated mixed hydra cell preparation indicated that the average number of laminin binding sites per cell was about 10,000 with a diss ociation constant of 1.49 nM. These binding sites could be displaced w ith unlabelled laminin in a dose-dependent manner and with high concen trations (500 nM) of unlabelled fibronectin. No displacement with type -IV collagen and type-I collagen was observed. Immunoscreening studies with a battery of antibodies raised to mammalian extracellular matrix (ECM) binding proteins indicated potential cell surface binding sites for the anti-beta(1) integrin monoclonal antibody, mAb JG22. Cell adh esion studies indicated that mAb JG22 blocked binding of hydra cells t o laminin, but did not affect their binding to fibronectin, type-IV co llagen, or type-I collagen. Light and electron microscopic immunocytoc hemical studies indicated that mAb JG22 localized to the basal plasma membrane of ectodermal and endodermal epithelial cells. Immunoprecipit ation studies identified two major bands with masses of about 196 kDa and 150 kDa under reducing conditions, and two bands with masses of >2 00 kDa under non-reducing conditions. Functional studies indicated tha t mAb JG22 could reversibly block morphogenesis of hydra cell aggregat es, and could block in vivo interstitial cell migration in hydra graft s. These observations indicate that hydra has cell surface binding sit es for ECM components which are functionally important during developm ent of this simple Cnidarian.