BEN/SC1/DM-GRASP, a homophilic adhesion molecule, is required for in vitro myeloid colony formation by avian hemopoietic progenitors

BEN/SC1/DM-GRASP is a membrane glycoprotein of the immunoglobulin superfamily isolated in the chick by several groups, including ours, Its expression is strictly developmentally regulated in several cell types of the nervous and hemopoietic systems and in certain epithelia, Each of these cell types expresses isoforms of BEN which differ by their level of N-glycosylation and by the presence or absence of the HNK-1 carbohydrate epitope. In the present work, the influence of glycosylation on BEN homophilic binding properties was investigated by two in vitro assays, First, each BEN isoform was covalently coupled to microspheres carrying different fluorescent dyes and an aggregation test was performed, We found that homophilic aggregates form indifferently between the same or different BEN isoforms, showing that glycosylation does not affect BEN hemophilic binding properties, This was confirmed in the second test, where the BEN-coated microspheres bound to the neurites of BEN-expressing neurons, irrespective of the isoform considered, The transient expression of the BEN antigen on hemopoietic progenitors prompted us to see whether it might play a role in their proliferation and differentiation. When added to hemopoietic progenitor cells in an in vitro colony formation assay anti-BEN immunoglobulin strongly inhibited myeloid, but not erythroid, colony formation although both types of precursors express the molecule.