ANTIBODIES AGAINST DOMAIN E3 OF LAMININ-1 AND INTEGRIN ALPHA-6 SUBUNIT PERTURB BRANCHING EPITHELIAL MORPHOGENESIS OF SUBMANDIBULAR-GLAND, BUT BY DIFFERENT MODES

Branching epithelial morphogenesis requires interactions between the s urrounding mesenchyme and the epithelium, as well as interactions betw een basement membrane components and the epithelium. Embryonic submand ibular gland was used to study the roles of two mesenchymal proteins, epimorphin and tenascin-C, as well as the epithelial protein laminin-1 and one of its integrin receptors on branching morphogenesis. Laminin -1 is a heterotrimer composed of an alpha 1 chain and two smaller chai ns (beta 1 and gamma 1). Immunofluorescence revealed a transient expre ssion of laminin alpha 1 chain in the epithelial basement membrane dur ing early stages of branching morphogenesis. Other laminin-1 chains an d alpha 6, beta 1, and beta 4 integrin subunits seemed to be expressed constitutively. Expression of epimorphin, but not tenascin-C, was see n in the mesenchyme during early developmental stages, but a mAb again st epimorphin did not perturb branching morphogenesis of this early ep ithelium. In contrast, inhibition of branching morphogenesis was seen with a mAb against the carboxy terminus of laminin alpha 1 chain, the E3 domain. An inhibition of branching was also seen with a mAb against the integrin alpha 6 subunit. The antibodies against laminin alpha 1 chain and integrin alpha 6 subunit perturbed development in distinct f ashions. Whereas treatment with the anti-E3 resulted in discontinuitie s of the basement membrane at the tips of the branching epithelium, tr eatment with the mAb against alpha 6 integrin subunit seemed to leave the basement membrane intact. We suggest that the laminin E3 domain is involved in basement membrane formation, whereas alpha 6 beta 1 integ rin binding to laminin-1 may elicit differentiation signals to the epi thelial cells.